the present invention relates to nucleotide sequences of the genome of pwd circovirus selected from the sequences seq id no . 1 , seq id no . 5 , seq id no . 15 , seq id no . 19 or one of their fragments . the nucleotide sequences of sequences seq id no . 1 and seq id no . 5 correspond respectively to the genome sequence of the strand of (+) polarity and of the strand of (−) polarity of the pwd circovirus of type a ( or pcva ), the sequence seq id no . 5 being represented according to the orientation 5 ′→ 3 ′. the nucleotide sequences of sequences seq id no . 15 and seq id no . 19 correspond respectively to the genome sequence of the strand of (+) polarity and of the strand of (−) polarity of the pwd circovirus of type b ( or pcvb ), the sequence seq id no . 19 being represented according to the orientation 5 ′→ 3 ′. the present invention likewise relates to nucleotide sequences , characterized in that they are selected from : a ) a nucleotide sequence of a specific fragment of the sequence seq id no . 1 , seq id no . 5 , seq id no . 15 , seq id no . 19 or one of their fragments ; b ) a nucleotide sequence homologous to a nucleotide sequence such as defined in a ); c ) a nucleotide sequence complementary to a nucleotide sequence such as defined in a ) or b ), and a nucleotide sequence of their corresponding rna ; d ) a nucleotide sequence capable of hybridizing under stringent conditions with a sequence such as defined in a ), b ) or c ); e ) a nucleotide sequence comprising a sequence such as defined in a ), b ), c ) or d ); and f ) a nucleotide sequence modified by a nucleotide sequence such as defined in a ), b ), c ), d ) or e ). nucleotide , polynucleotide or nucleic acid sequence will be understood according to the present invention as meaning both a double - stranded or single - stranded dna in the monomeric and dimeric ( so - called in tandem ) forms and the transcription products of said dnas . it must be understood that the present invention does not relate to the genomic nucleotide sequences taken in their natural environment , that is to say in the natural state . it concerns sequences which it has been possible to isolate , purify or partially purify , starting from separation methods such as , for example , ion - exchange chromatography , by exclusion based on molecular size , or by affinity , or alternatively fractionation techniques based on solubility in different solvents , or starting from methods of genetic engineering such as amplification , cloning and subcloning , it being possible for the sequences of the invention to be carried by vectors . the nucleotide sequences seq id no . 1 and seq id no . 15 were obtained by sequencing of the genome by the sanger method . nucleotide sequence fragment according to the invention will be understood as designating any nucleotide fragment of the pwd circovirus , type a or b , of length of at least 8 nucleotides , preferably at least 12 nucleotides , and even more preferentially at least 20 consecutive nucleotides of the sequence from which it originates . specific fragment of a nucleotide sequence according to the invention will be understood as designating any nucleotide fragment of the pwd circovirus , type a or b , having , after alignment and comparison with the corresponding fragments of known porcine circoviruses , at least one nucleotide or base of different nature . for example , the specific nucleotide fragments of the pwd circovirus of type a can easily be determined by referring to fig3 of the present invention in which the nucleotides or bases of the sequence seq id no . 1 ( circopordfp ) are shown which are of different nature , after alignment of said sequence seq id no . 1 with the other two sequences of known porcine circovirus ( circopormeeh and circopormank ). homologous nucleotide sequence in the sense of the present invention is understood as meaning a nucleotide sequence having at least a percentage identity with the bases of a nucleotide sequence according to the invention of at least 80 %, preferably 90 % or 95 %, this percentage being purely statistical and it being possible to distribute the differences between the two nucleotide sequences at random and over the whole of their length . specific homologous nucleotide sequence in the sense of the present invention is understood as meaning a homologous nucleotide sequence having at least one nucleotide sequence of a specific fragment , such as defined above . said “ specific ” homologous sequences can comprise , for example , the sequences corresponding to the genomic sequence or to the sequences of its fragments representative of variants of pwd circovirus of type a or b . these specific homologous sequences can thus correspond to variations linked to mutations within strains of pwd circovirus of type a and b , and especially correspond to truncations , substitutions , deletions and / or additions of at least one nucleotide . said homologous sequences can likewise correspond to variations linked to the degeneracy of the genetic code . the term “ degree or percentage of sequence homology ” refers to “ degree or percentage of sequence identity between two sequences after optimal alignment ” as defined in the present application . two amino - acids or nucleotidic sequences are said to be “ identical ” if the sequence of amino - acids or nucleotidic residues , in the two sequences is the same when aligned for maximum correspondence as described below . sequence comparisons between two ( or more ) peptides or polynucleotides are typically performed by comparing sequences of two optimally aligned sequences over a segment or “ comparison window ” to identify and compare local regions of sequence similarity . optimal alignment of sequences for comparison may be conducted by the local homology algorithm of smith and waterman , ad . app . math 2 : 482 ( 1981 ), by the homology alignment algorithm of neddleman and wunsch , j . mol . biol . 48 : 443 ( 1970 ), by the search for similarity method of pearson and lipman , proc . natl . acad . sci . ( u . s . a .) 85 : 2444 ( 1988 ), by computerized implementation of these algorithms ( gap , bestfit , fasta , and tfasta in the wisconsin genetics software package , genetics computer group ( gcg ), 575 science dr ., madison , wis . ), or by visual inspection . “ percentage of sequence identity ” ( or degree or identity ) is determined by comparing two optimally aligned sequences over a comparison window , where the portion of the peptide or polynucleotide sequence in the comparison window may comprise additions or deletions ( i . e ., gaps ) as compared to the reference sequence ( which does not comprise additions or deletions ) for optimal alignment of the two sequences . the percentage is calculated by determining the number of positions at which the identical amino - acid residue or nucleic acid base occurs in both sequences to yield the number of matched positions , dividing the number of matched positions by the total number of positions in the window of comparison and multiplying the result by 100 to yield the percentage of sequence identity . the definition of sequence identity given above is the definition that would use one of skill in the art . the definition by itself does not need the help of any algorithm , said algorithms being helpful only to achieve the optimal alignments of sequences , rather than the calculation of sequence identity . from the definition given above , it follows that there is a well defined and only one value for the sequence identity between two compared sequences which value corresponds to the value obtained for the best or optimal alignment . in the blast n or blast p “ blast 2 sequence ”, software which is available in the web site http :// www . ncbi . nlm . nih . gov / gorf / bl2 . html , and habitually used by the inventors and in general by the skilled man for comparing and determining the identity between two sequences , gap cost which depends on the sequence length to be compared is directly selected by the software ( i . e . 11 . 2 for substitution matrix blosum - 62 for length & gt ; 85 ). in the present description , pwd circovirus will be understood as designating the circoviruses associated with piglet weight loss disease ( pwd ) of type a ( pcva ) or type b ( pcvb ), defined below by their genomic sequence , as well as the circoviruses whose nucleic sequences are homologous to the sequences of pwd circoviruses of type a or b , such as in particular the circoviruses corresponding to variants of the type a or of the type b . complementary nucleotide sequence of a sequence of the invention is understood as meaning any dna whose nucleotides are complementary to those of the sequence of the invention , and whose orientation is reversed ( antiparallel sequence ). hybridization under conditions of stringency with a nucleotide sequence according to the invention is understood as meaning a hybridization under conditions of temperature and ionic strength chosen in such a way that they allow the maintenance of the hybridization between two fragments of complementary dna . by way of illustration , conditions of great stringency of the hybridization step with the aim of defining the nucleotide fragments described above are advantageously the following . the hybridization is carried out at a preferential temperature of 65 ° c . in the presence of ssc buffer , 1 × ssc corresponding to 0 . 15 m nacl and 0 . 05 m na citrate . the washing steps , for example , can be the following : 2 × ssc , at ambient temperature followed by two washes with 2 × ssc , 0 . 5 % sds at 65 ° c . ; 2 × 0 . 5 × ssc , 0 . 5 % sds ; at 65 ° c . for 10 minutes each . the conditions of intermediate stringency , using , for example , a temperature of 42 ° c . in the presence of a 2 × ssc buffer , or of less stringency , for example a temperature of 37 ° c . in the presence of a 2 × ssc buffer , respectively require a globally less significant complementarity for the hybridization between the two sequences . the stringent hybridization conditions described above for a polynucleotide with a size of approximately 350 bases will be adapted by the person skilled in the art for oligonucleotides of greater or smaller size , according to the teaching of sambrook et al ., 1989 . among the nucleotide sequences according to the invention , those are likewise preferred which can be used as a primer or probe in methods allowing the homologous sequences according to the invention to be obtained , these methods , such as the polymerase chain reaction ( pcr ), nucleic acid cloning and sequencing , being well known to the person skilled in the art . among said nucleotide sequences according to the invention , those are again preferred which can be used as a primer or probe in methods allowing the presence of pwd circovirus or one of its variants such as defined below to be diagnosed . the nucleotide sequences according to the invention capable of modulating , of inhibiting or of inducing the expression of pwd circovirus gene , and / or capable of modulating the replication cycle of pwd circovirus in the host cell and / or organism are likewise preferred . replication cycle will be understood as designating the invasion and the multiplication of pwd circovirus , and its propagation from host cell to host cell in the host organism . among said nucleotide sequences according to the invention , those corresponding to open reading frames , called orf sequences , and coding for polypeptides , such as , for example , the sequences seq id no . 9 ( orf1 ), seq id no . 11 ( orf2 ) and seq id no . 13 ( orf3 ) respectively corresponding to the nucleotide sequences between the positions 47 and 985 determined with respect to the position of the nucleotides on the sequence seq id no . 1 , the positions 1723 and 1022 and the positions 658 and 38 with respect to the position of the nucleotides on the sequence seq id no . 5 ( represented according to the orientation 3 ′→ 5 ′), the ends being included , or alternatively the sequences seq id no . 23 ( orf ′ 1 ), seq id no . 25 ( orf ′ 2 ) and seq id no . 27 ( orf ′ 3 ), respectively corresponding to the sequences between the positions 51 and 995 determined with respect to the position of the nucleotides on the sequence seq id no . 15 , the positions 1734 and 1033 and the positions 670 and 357 , the positions being determined with respect to the position of the nucleotides on the sequence seq id no . 19 ( represented according to the orientation 3 ′→ 5 ′), the ends being included , are finally preferred . the nucleotide sequence fragments according to the invention can be obtained , for example , by specific amplification , such as pcr , or after digestion with appropriate restriction enzymes of nucleotide sequences according to the invention , these methods in particular being described in the work of sambrook et al ., 1989 . said representative fragments can likewise be obtained by chemical synthesis when their size is not very large and according to methods well known to persons skilled in the art . modified nucleotide sequence will be understood as meaning any nucleotide sequence obtained by mutagenesis according to techniques well known to the person skilled in the art , and containing modifications with respect to the normal sequences according to the invention , for example mutations in the regulatory and / or promoter sequences of polypeptide expression , especially leading to a modification of the rate of expression of said polypeptide or to a modulation of the replicative cycle . modified nucleotide sequence will likewise be understood as meaning any nucleotide sequence coding for a modified polypeptide such as defined below . the present invention relates to nucleotide sequences of pwd circovirus according to the invention , characterized in that they are selected from the sequences seq id no . 9 , seq id no . 11 , seq id no . 13 , seq id no . 23 , seq id no . 25 , seq id no . 27 or one of their fragments . the invention likewise relates to nucleotide sequences characterized in that they comprise a nucleotide sequence selected from : a ) a nucleotide sequence seq id no . 9 , seq id no . 11 , seq id no . 13 , seq id no . 23 , seq id no . 25 , seq id no . 27 or one of their fragments ; b ) a nucleotide sequence of a specific fragment of a sequence such as defined in a ); c ) a homologous nucleotide sequence having at least 80 % identity with a sequence such as defined in a ) or b ); d ) a complementary nucleotide sequence or sequence of rna corresponding to a sequence such as defined in a ), b ) or c ); and e ) a nucleotide sequence modified by a sequence such as defined in a ), b ), c ) or d ). as far as homology with the nucleotide sequences seq id no . 9 , seq id no . 11 , seq id no . 13 , seq id no . 23 , seq id no . 25 , seq id no . 27 or one of their fragments is concerned , the homologous , especially specific , sequences having a percentage identity with one of the sequences seq id no . 9 , seq id no . 11 , seq id no . 13 , seq id no . 23 , seq id no . 25 , seq id no . 27 or one of their fragments of at least 80 %, preferably 90 % or 95 %, are preferred . said specific homologous sequences can comprise , for example , the sequences corresponding to the sequences orf1 , orf2 , orf3 , orf ′ 1 , orf ′ 2 and orf ′ 3 of pwd circovirus variants of type a or of type b . in the same manner , these specific homologous sequences can correspond to variations linked to mutations within strains of pwd circovirus of type a or of type b and especially correspond to truncations , substitutions , deletions and / or additions of at least one nucleotide . among nucleotide sequences according to the invention , the sequence seq id no . 23 which has a homology having more than 80 % identity with the sequence seq id no . 9 , as well as the sequence seq id no . 25 , are especially preferred . preferably , the invention relates to the nucleotide sequences according to the invention , characterized in that they comprise a nucleotide sequence selected from the following sequences : a ) seq id no . 33 170 5 ′ tg t gg c ga 3 ′; b ) seq id no . 34 450 5 ′ ag t ttcct 3 ′; c ) seq id no . 35 1026 5 ′ t c atttagagggtcttt c ag 3 ′; d ) seq id no . 36 1074 5 ′ gtca a cct 3 ′; e ) seq id no . 37 1101 5 ′ gtgg t tgc 3 ′; f ) seq id no . 38 1123 5 ′ agcc c agg 3 ′; g ) seq id no . 39 1192 5 ′ ttgg c tgg 3 ′; h ) seq id no . 40 1218 5 ′ tc t agctc t ggt 3 ′; i ) seq id no . 41 1501 5 ′ atct c ag c t c gt 3 ′; j ) seq id no . 42 1536 5 ′ t g tcctcct c tt 3 ′; k ) seq id no . 43 1563 5 ′ tct c taga 3 ′; l ) seq id no . 44 1623 5 ′ tgt a ccaa 3 ′; m ) seq id no . 45 1686 5 ′ tcc g tctt 3 ′; in the list of nucleotide sequences a )- m ) above , the underlined nucleotides are mutated with respect to the two known sequences of circovirus which are nonpathogenic to pigs . the number preceding the nucleotide sequence represents the position of the first nucleotide of said sequence in the sequence seq id no . 1 . the invention comprises the polypeptides encoded by a nucleotide sequence according to the invention , preferably a polypeptide whose sequence is represented by a fragment , especially a specific fragment , of one of the six sequences of amino acids represented in fig2 , these six amino acid sequences corresponding to the polypeptides which can be encoded according to one of the three possible reading frames of the sequence seq id no . 1 or of the sequence seq id no . 5 , or a polypeptide whose sequence is represented by a fragment , especially a specific fragment , of one of the six sequences of amino acids shown in fig8 , these six sequences of amino acids corresponding to the polypeptides which can be encoded according to one of the three possible reading frames of the sequence seq id no . 15 or of the sequence seq id no . 19 . the invention likewise relates to the polypeptides , characterized in that they comprise a polypeptide selected from the amino acid sequences seq id no . 10 , seq id no . 12 , seq id no . 14 , seq id no . 24 , seq id no . 26 , seq id no . 28 or one of their fragments . among the polypeptides according to the invention , the polypeptide of amino acid sequence seq id no . 24 which has a homology having more than 80 % identity with the sequence seq id no . 10 , as well as the polypeptide of sequence seq id no . 26 , are especially preferred . the invention also relates to the polypeptides , characterized in that they comprise a polypeptide selected from : a ) a specific fragment of at least 5 amino acids of a polypeptide of an amino acid sequence according to the invention ; c ) a specific biologically active fragment of a polypeptide such as defined in a ) or b ); and d ) a polypeptide modified by a polypeptide such as defined in a ), b ) or c ). among the polypeptides according to the invention , the polypeptides of amino acid sequences seq id no . 29 , seq id no . 30 , seq id no . 31 and seq id no . 32 are also preferred , these polypeptides being especially capable of specifically recognizing the antibodies produced during infection by the pwd circovirus of type b . these polypeptides thus have epitopes specific for the pwd circovirus of type b and can thus be used in particular in the diagnostic field or as immunogenic agent to confer protection in pigs against infection by pwd circovirus , especially of type b . in the present description , the terms polypeptide , peptide and protein are interchangeable . it must be understood that the invention does not relate to the polypeptides in natural form , that is to say that they are not taken in their natural environment but that they can be isolated or obtained by purification from natural sources , or else obtained by genetic recombination , or alternatively by chemical synthesis and that they can thus contain unnatural amino acids , as will be described below . polypeptide fragment according to the invention is understood as designating a polypeptide containing at least 5 consecutive amino acids , preferably 10 consecutive amino acids or 15 consecutive amino acids . in the present invention , specific polypeptide fragment is understood as designating the consecutive polypeptide fragment encoded by a specific fragment nucleotide sequence according to the invention . homologous polypeptide will be understood as designating the polypeptides having , with respect to the natural polypeptide , certain modifications such as , in particular , a deletion , addition or substitution of at least one amino acid , a truncation , a prolongation , a chimeric fusion , and / or a mutation . among the homologous polypeptides , those are preferred whose amino acid sequence has at least 80 %, preferably 90 %, homology with the sequences of amino acids of polypeptides according to the invention . specific homologous polypeptide will be understood as designating the homologous polypeptides such as defined above and having a specific fragment of polypeptide according to the invention . in the case of a substitution , one or more consecutive or nonconsecutive amino acids are replaced by “ equivalent ” amino acids . the expression “ equivalent ” amino acid is directed here at designating any amino acid capable of being substituted by one of the amino acids of the base structure without , however , essentially modifying the biological activities of the corresponding peptides and such that they will be defined by the following . these equivalent amino acids can be determined either by depending on their structural homology with the amino acids which they substitute , or on results of comparative tests of biological activity between the different polypeptides , which are capable of being carried out . by way of example , the possibilities of substitutions capable of being carried out without resulting in an extensive modification of the biological activity of the corresponding modified polypeptides will be mentioned , the replacement , for example , of leucine by valine or isoleucine , of aspartic acid by glutamic acid , of glutamine by asparagine , of arginine by lysine etc ., the reverse substitutions naturally being envisageable under the same conditions . the specific homologous polypeptides likewise correspond to polypeptides encoded by the specific homologous nucleotide sequences such as defined above and thus comprise in the present definition the polypeptides which are mutated or correspond to variants which can exist in pwd circovirus , and which especially correspond to truncations , substitutions , deletions and / or additions of at least one amino acid residue . specific biologically active fragment of a polypeptide according to the invention will be understood in particular as designating a specific polypeptide fragment , such as defined above , having at least one of the characteristics of polypeptides according to the invention , especially in that it is : capable of inducing an immunogenic reaction directed against a pwd circovirus ; and / or capable of being recognized by a specific antibody of a polypeptide according to the invention ; and / or capable of linking to a polypeptide or to a nucleotide sequence of pwd circovirus ; and / or capable of exerting a physiological activity , even partial , such as , for example , a dissemination or structural ( capsid ) activity ; and / or capable of modulating , of inducing or of inhibiting the expression of pwd circovirus gene or one of its variants , and / or capable of modulating the replication cycle of pwd circovirus in the cell and / or the host organism . the polypeptide fragments according to the invention can correspond to isolated or purified fragments naturally present in a pwd circovirus or correspond to fragments which can be obtained by cleavage of said polypeptide by a proteolytic enzyme , such as trypsin or chymotrypsin or collagenase , or by a chemical reagent , such as cyanogen bromide ( cnbr ) or alternatively by placing said polypeptide in a very acidic environment , for example at ph 2 . 5 . such polypeptide fragments can likewise just as easily be prepared by chemical synthesis , from hosts transformed by an expression vector according to the invention containing a nucleic acid allowing the expression of said fragments , placed under the control of appropriate regulation and / or expression elements . “ modified polypeptide ” of a polypeptide according to the invention is understood as designating a polypeptide obtained by genetic recombination or by chemical synthesis as will be described below , having at least one modification with respect to the normal sequence . these modifications will especially be able to bear on amino acids at the origin of a specificity , of pathogenicity and / or of virulence , or at the origin of the structural conformation , and of the capacity of membrane insertion of the polypeptide according to the invention . it will thus be possible to create polypeptides of equivalent , increased or decreased activity , and of equivalent , narrower , or wider specificity . among the modified polypeptides , it is necessary to mention the polypeptides in which up to 5 amino acids can be modified , truncated at the n - or c - terminal end , or even deleted or added . as is indicated , the modifications of the polypeptide will especially have as objective : to render it capable of modulating , of inhibiting or of inducing the expression of pwd circovirus gene and / or capable of modulating the replication cycle of pwd circovirus in the cell and / or the host organism , the methods allowing said modulations on eukaryotic or prokaryotic cells to be demonstrated are well known to the person skilled in the art . it is likewise well understood that it will be possible to use the nucleotide sequences coding for said modified polypeptides for said modulations , for example through vectors according to the invention and described below , in order , for example , to prevent or to treat the pathologies linked to the infection . the preceding modified polypeptides can be obtained by using combinatorial chemistry , in which it is possible to systematically vary parts of the polypeptide before testing them on models , cell cultures or microorganisms for example , to select the compounds which are most active or have the properties sought . chemical synthesis likewise has the advantage of being able to use : thus , in order to improve the duration of life of the polypeptides according to the invention , it may be of interest to use unnatural amino acids , for example in d form , or else amino acid analogs , especially sulfur - containing forms , for example . finally , it will be possible to integrate the structure of the polypeptides according to the invention , its specific or modified homologous forms , into chemical structures of polypeptide type or others . thus , it may be of interest to provide at the n - and c - terminal ends compounds not recognized by the proteases . the nucleotide sequences coding for a polypeptide according to the invention are likewise part of the invention . the invention likewise relates to nucleotide sequences utilizable as a primer or probe , characterized in that said sequences are selected from the nucleotide sequences according to the invention . among the pairs of nucleotide sequences utilizable as a pair of primers according to the invention , the pairs of primers selected from the following pairs are preferred : the cloning and the sequencing of the pwd circovirus , type a and b , has allowed it to be identified , after comparative analysis with the nucleotide sequences of other porcine circoviruses , that , among the sequences of fragments of these nucleic acids , were those which are strictly specific to the pwd circovirus of type a , of type b or of type a and b , and those which correspond to a consensus sequence of porcine circoviruses other than the pwd circoviruses of type a and / or b . there is likewise a great need for nucleotide sequences utilizable as a primer or probe specific to the whole of the other known and nonpathogenic porcine circoviruses . said consensus nucleotide sequences specific to all circoviruses , other than pwd circovirus of type a and b , are easily identifiable from fig3 and the sequence seq id no . 15 , and are part of the invention . among said consensus nucleotide sequences , that which is characterized in that it is part of the following pair of primers is preferred : the invention likewise comprises a nucleotide sequence according to the invention , characterized in that said sequence is a specific consensus sequence of porcine circovirus other than pwd circovirus of type b and in that it is one of the primers of the following pairs of primers : it is well understood that the present invention likewise relates to specific polypeptides of known porcine circoviruses other than pwd circovirus , encoded by said consensus nucleotide sequences , capable of being obtained by purification from natural polypeptides , by genetic recombination or by chemical synthesis by procedures well known to the person skilled in the art and such as described in particular below . in the same manner , the labeled or unlabeled mono - or polyclonal antibodies directed against said specific polypeptides encoded by said consensus nucleotide sequences are also part of the invention . it will be possible to use said consensus nucleotide sequences , said corresponding polypeptides as well as said antibodies directed against said polypeptides in procedures or sets for detection and / or identification such as described below , in place of or in addition to nucleotide sequences , polypeptides or antibodies according to the invention , specific to pwd circovirus type a and / or b . these protocols have been improved for the differential detection of the circular monomeric forms of specific replicative forms of the virion or of the dna in replication and the dimeric forms found in so - called in - tandem molecular constructs . the invention additionally relates to the use of a nucleotide sequence according to the invention as a primer or probe for the detection and / or the amplification of nucleic acid sequences . the nucleotide sequences according to the invention can thus be used to amplify nucleotide sequences , especially by the pcr technique ( polymerase chain reaction ) ( erlich , 1989 ; innis et al ., 1990 ; rolfs et al ., 1991 ; and white et al ., 1997 ). these oligodeoxyribonucleotide or oligoribonucleotide primers advantageously have a length of at least 8 nucleotides , preferably of at least 12 nucleotides , and even more preferentially at least 20 nucleotides . other amplification techniques of the target nucleic acid can be advantageously employed as alternatives to pcr . the nucleotide sequences of the invention , in particular the primers according to the invention , can likewise be employed in other procedures of amplification of a target nucleic acid , such as : the tas technique ( transcription - based amplification system ), described by kwoh et al . in 1989 ; the 3sr technique ( self - sustained sequence replication ), described by guatelli et al . in 1990 ; the nasba technique ( nucleic acid sequence based amplification ), described by kievitis et al . in 1991 ; the sda technique ( strand displacement amplification ) ( walker et al ., 1992 ); the tma technique ( transcription mediated amplification ). the polynucleotides of the invention can also be employed in techniques of amplification or of modification of the nucleic acid serving as a probe , such as : the lcr technique ( ligase chain reaction ), described by landegren et al . in 1988 and improved by barany et al . in 1991 , which employs a thermostable ligase ; the rcr technique ( repair chain reaction ), described by segev in 1992 ; the cpr technique ( cycling probe reaction ), described by duck et al . in 1990 ; the amplification technique with q - beta replicase , described by miele et al . in 1983 and especially improved by chu et al . in 1986 , lizardi et al . in 1988 , then by burg et al . as well as by stone et al . in 1996 . in the case where the target polynucleotide to be detected is possibly an rna , for example an mrna , it will be possible to use , prior to the employment of an amplification reaction with the aid of at least one primer according to the invention or to the employment of a detection procedure with the aid of at least one probe of the invention , an enzyme of reverse transcriptase type in order to obtain a cdna from the rna contained in the biological sample . the cdna obtained will thus serve as a target for the primer ( s ) or the probe ( s ) employed in the amplification or detection procedure according to the invention . the detection probe will be chosen in such a manner that it hybridizes with the target sequence or the amplicon generated from the target sequence . by way of sequence , such a probe will advantageously have a sequence of at least 12 nucleotides , in particular of at least 20 nucleotides , and preferably of at least 100 nucleotides . the invention also comprises the nucleotide sequences utilizable as a probe or primer according to the invention , characterized in that they are labeled with a radioactive compound or with a nonradioactive compound . the unlabeled nucleotide sequences can be used directly as probes or primers , although the sequences are generally labeled with a radioactive element ( 32 p , 35 s , 3 h , 125 i ) or with a nonradioactive molecule ( biotin , acetylaminofluorene , digoxigenin , 5 - bromodeoxyuridine , fluorescein ) to obtain probes which are utilizable for numerous applications . examples of nonradioactive labeling of nucleotide sequences are described , for example , in french patent no . 78 . 10975 or by urdea et al . or by sanchez - pescador et al . in 1988 . in the latter case , it will also be possible to use one of the labeling methods described in patents fr - 2 422 956 and fr - 2 518 755 . the hybridization technique can be carried out in various manners ( matthews et al ., 1988 ). the most general method consists in immobilizing the nucleic acid extract of cells on a support ( such as nitrocellulose , nylon , polystyrene ) and in incubating , under well - defined conditions , the immobilized target nucleic acid with the probe . after hybridization , the excess of probe is eliminated and the hybrid molecules formed are detected by the appropriate method ( measurement of the radioactivity , of the fluorescence or of the enzymatic activity linked to the probe ). the invention likewise comprises the nucleotide sequences according to the invention , characterized in that they are immobilized on a support , covalently or noncovalently . according to another advantageous mode of employing nucleotide sequences according to the invention , the latter can be used immobilized on a support and can thus serve to capture , by specific hybridization , the target nucleic acid obtained from the biological sample to be tested . if necessary , the solid support is separated from the sample and the hybridization complex formed between said capture probe and the target nucleic acid is then detected with the aid of a second probe , a so - called detection probe , labeled with an easily detectable element . another subject of the present invention is a vector for the cloning and / or expression of a sequence , characterized in that it contains a nucleotide sequence according to the invention . the vectors according to the invention , characterized in that they contain the elements allowing the expression and / or the secretion of said nucleotide sequences in a determined host cell , are likewise part of the invention . the vector must then contain a promoter , signals of initiation and termination of translation , as well as appropriate regions of regulation of transcription . it must be able to be maintained stably in the host cell and can optionally have particular signals specifying the secretion of the translated protein . these different elements are chosen as a function of the host cell used . to this end , the nucleotide sequences according to the invention can be inserted into autonomous replication vectors within the chosen host , or integrated vectors of the chosen host . such vectors will be prepared according to the methods currently used by the person skilled in the art , and it will be possible to introduce the clones resulting therefrom into an appropriate host by standard methods , such as , for example , lipofection , electroporation and thermal shock . the vectors according to the invention are , for example , vectors of plasmid or viral origin . a preferred vector for the expression of polypeptides of the invention is baculovirus . the vector pbs ks in which is inserted the in - tandem dna sequence of the pwd circovirus type a ( or dfp ) as deposited at the cncm on 3 jul . 1997 , under the number i - 1891 , is likewise preferred . these vectors are useful for transforming host cells in order to clone or to express the nucleotide sequences of the invention . the invention likewise comprises the host cells transformed by a vector according to the invention . these cells can be obtained by the introduction into host cells of a nucleotide sequence inserted into a vector such as defined above , then the culturing of said cells under conditions allowing the replication and / or expression of the transfected nucleotide sequence . the host cell can be selected from prokaryotic or eukaryotic systems , such as , for example , bacterial cells ( olins and lee , 1993 ), but likewise yeast cells ( buckholz , 1993 ), as well as animal cells , in particular the cultures of mammalian cells ( edwards and aruffo , 1993 ), and especially chinese hamster ovary ( cho ) cells , but likewise the cells of insects in which it is possible to use procedures employing baculoviruses , for example ( luckow , 1993 ). a preferred host cell for the expression of the proteins of the invention is constituted by sf9 insect cells . a more preferred host cell according to the invention is e . coli , such as deposited at the cncm on 3 jul . 1997 , under the number i - 1891 . the invention likewise relates to animals comprising one of said transformed cells according to the invention . the obtainment of transgenic animals according to the invention overexpressing one or more of the genes of pwd circovirus or part of the genes will be preferably carried out in rats , mice or rabbits according to methods well known to the person skilled in the art , such as by viral or nonviral transfections . it will be possible to obtain the transgenic animals overexpressing one or more of said genes by transfection of multiple copies of said genes under the control of a strong promoter of ubiquitous nature , or selective for one type of tissue . it will likewise be possible to obtain the transgenic animals by homologous recombination in embryonic cell strains , transfer of these cell strains to embryos , selection of the affected chimeras at the level of the reproductive lines , and growth of said chimeras . the transformed cells as well as the transgenic animals according to the invention are utilizable in procedures for preparation of recombinant polypeptides . it is today possible to produce recombinant polypeptides in relatively large quantity by genetic engineering using the cells transformed by expression vectors according to the invention or using transgenic animals according to the invention . the procedures for preparation of a polypeptide of the invention in recombinant form , characterized in that they employ a vector and / or a cell transformed by a vector according to the invention and / or a transgenic animal comprising one of said transformed cells according to the invention , are themselves comprised in the present invention . among said procedures for preparation of a polypeptide of the invention in recombinant form , the preparation procedures employing a vector , and / or a cell transformed by said vector and / or a transgenic animal comprising one of said transformed cells , containing a nucleotide sequence according to the invention coding for a polypeptide of pwd circovirus , are preferred . the recombinant polypeptides obtained as indicated above can just as well be present in glycosylated form as in nonglycosylated form and can or cannot have the natural tertiary structure . a preferred variant consists in producing a recombinant polypeptide used to a “ carrier ” protein ( chimeric protein ). the advantage of this system is that it allows a stabilization of and a decrease in the proteolysis of the recombinant product , an increase in the solubility in the course of renaturation in vitro and / or a simplification of the purification when the fusion partner has an affinity for a specific ligand . more particularly , the invention relates to a procedure for preparation of a polypeptide of the invention comprising the following steps : a ) culture of transformed cells under conditions allowing the expression of a recombinant polypeptide of nucleotide sequence according to the invention ; b ) if need be , recovery of said recombinant polypeptide . when the procedure for preparation of a polypeptide of the invention employs a transgenic animal according to the invention , the recombinant polypeptide is then extracted from said animal . the invention also relates to a polypeptide which is capable of being obtained by a procedure of the invention such as described previously . the invention also comprises a procedure for preparation of a synthetic polypeptide , characterized in that it uses a sequence of amino acids of polypeptides according to the invention . the invention likewise relates to a synthetic polypeptide obtained by a procedure according to the invention . the polypeptides according to the invention can likewise be prepared by techniques which are conventional in the field of the synthesis of peptides . this synthesis can be carried out in homogeneous solution or in solid phase . for example , recourse can be made to the technique of synthesis in homogeneous solution described by houben - weyl in 1974 . this method of synthesis consists in successively condensing , two by two , the successive amino acids in the order required , or in condensing amino acids and fragments formed previously and already containing several amino acids in the appropriate order , or alternatively several fragments previously prepared in this way , it being understood that it will be necessary to protect beforehand all the reactive functions carried by these amino acids or fragments , with the exception of amine functions of one and carboxyls of the other or vice - versa , which must normally be involved in the formation of peptide bonds , especially after activation of the carboxyl function , according to the methods well known in the synthesis of peptides . according to another preferred technique of the invention , recourse will be made to the technique described by merrifield . to make a peptide chain according to the merrifield procedure , recourse is made to a very porous polymeric resin , on which is immobilized the first c - terminal amino acid of the chain . this amino acid is immobilized on a resin through its carboxyl group and its amine function is protected . the amino acids which are going to form the peptide chain are thus immobilized , one after the other , on the amino group , which is deprotected beforehand each time , of the portion of the peptide chain already formed , and which is attached to the resin . when the whole of the desired peptide chain has been formed , the protective groups of the different amino acids forming the peptide chain are eliminated and the peptide is detached from the resin with the aid of an acid . the invention additionally relates to hybrid polypeptides having at least one polypeptide according to the invention , and a sequence of a polypeptide capable of inducing an immune response in man or animals . advantageously , the antigenic determinant is such that it is capable of inducing a humoral and / or cellular response . it will be possible for such a determinant to comprise a polypeptide according to the invention in glycosylated form used with a view to obtaining immunogenic compositions capable of inducing the synthesis of antibodies directed against multiple epitopes . said polypeptides or their glycosylated fragments are likewise part of the invention . these hybrid molecules can be formed , in part , of a polypeptide carrier molecule or of fragments thereof according to the invention , associated with a possibly immunogenic part , in particular an epitope of the diphtheria toxin , the tetanus toxin , a surface antigen of the hepatitis b virus ( patent fr 79 21811 ), the vp1 antigen of the poliomyelitis virus or any other viral or bacterial toxin or antigen . the procedures for synthesis of hybrid molecules encompass the methods used in genetic engineering for constructing hybrid nucleotide sequences coding for the polypeptide sequences sought . it will be possible , for example , to refer advantageously to the technique for obtainment of genes coding for fusion proteins described by minton in 1984 . said hybrid nucleotide sequences coding for a hybrid polypeptide as well as the hybrid polypeptides according to the invention characterized in that they are recombinant polypeptides obtained by the expression of said hybrid nucleotide sequences are likewise part of the invention . the invention likewise comprises the vectors characterized in that they contain one of said hybrid nucleotide sequences . the host cells transformed by said vectors , the transgenic animals comprising one of said transformed cells as well as the procedures for preparation of recombinant polypeptides using said vectors , said transformed cells and / or said transgenic animals are , of course , likewise part of the invention . the polypeptides according to the invention , the antibodies according to the invention described below and the nucleotide sequences according to the invention can advantageously be employed in procedures for the detection and / or identification of pwd circovirus , or of porcine circovirus other than a pwd circovirus , in a biological sample ( biological tissue or fluid ) capable of containing them . these procedures , according to the specificity of the polypeptides , the antibodies and the nucleotide sequences according to the invention which will be used , will in particular be able to detect and / or to identify a pwd circovirus or a porcine circovirus other than a pwd circovirus or other than the pwd circovirus of type b . the polypeptides according to the invention can advantageously be employed in a procedure for the detection and / or the identification of pwd circovirus of type a , of type b , of type a or b , or porcine circovirus other than the pwd circovirus of type b , or of porcine circovirus other than the pwd circovirus of type a or b , in a biological sample ( biological tissue or fluid ) capable of containing them , characterized in that it comprises the following steps : a ) contacting of this biological sample with a polypeptide or one of its fragments according to the invention ( under conditions allowing an immunological reaction between said polypeptide and the antibodies possibly present in the biological sample ); b ) demonstration of the antigen - antibody complexes possibly formed . in the present description , pwd circovirus , except if a particular mention is indicated , will be understood as designating a pwd circovirus of type a or of type b , and porcine circovirus other than pwd , except if a particular mention is indicated , will be understood as designating a porcine circovirus other than a pwd circovirus of type a and b . preferably , the biological sample is formed by a fluid , for example a pig serum , whole blood or biopsies . any conventional procedure can be employed for carrying out such a detection of the antigen - antibody complexes possibly formed . by way of example , a preferred method brings into play immunoenzymatic processes according to the elisa technique , by immunofluorescence , or radioimmunological processes ( ria ) or their equivalent . thus , the invention likewise relates to the polypeptides according to the invention , labeled with the aid of an adequate label such as of the enzymatic , fluorescent or radioactive type . deposition of determined quantities of a polypeptide composition according to the invention in the wells of a microtiter plate , introduction into said wells of increasing dilutions of serum , or of a biological sample other than that defined previously , having to be analyzed , incubation of the microplate , introduction into the wells of the microtiter plate of labeled antibodies directed against pig immunoglobulins , the labeling of these antibodies having been carried out with the aid of an enzyme selected from those which are capable of hydrolyzing a substrate by modifying the absorption of the radiation of the latter , at least at a determined wavelength , for example at 550 nm , detection , by comparison with a control test , of the quantity of hydrolyzed substrate . the invention likewise relates to a kit or set for the detection and / or identification of pwd circovirus , of porcine circovirus other than a pwd circovirus or of porcine circovirus other than the pwd circovirus of type b , characterized in that it comprises the following elements : a polypeptide according to the invention , if need be , the reagents for the formation of the medium favorable to the immunological or specific reaction , if need be , the reagents allowing the detection of the antigen - antibody complexes produced by the immunological reaction between the polypeptide ( s ) of the invention and the antibodies possibly present in the biological sample , these reagents likewise being able to carry a label , or to be recognized in their turn by a labeled reagent , more particularly in the case where the polypeptide according to the invention is not labeled , if need be , a biological reference sample ( negative control ) devoid of antibodies recognized by a polypeptide according to the invention , if need be , a biological reference sample ( positive control ) containing a predetermined quantity of antibodies recognized by a polypeptide according to the invention . the polypeptides according to the invention allow monoclonal or polyclonal antibodies to be prepared which are characterized in that they specifically recognize the polypeptides according to the invention . it will advantageously be possible to prepare the monoclonal antibodies from hybridomas according to the technique described by kohler and milstein in 1975 . it will be possible to prepare the polyclonal antibodies , for example , by immunization of an animal , in particular a mouse , with a polypeptide or a dna , according to the invention , associated with an adjuvant of the immune response , and then purification of the specific antibodies contained in the serum of the immunized animals on an affinity column on which the polypeptide which has served as an antigen has previously been immobilized . the polyclonal antibodies according to the invention can also be prepared by purification , on an affinity column on which a polypeptide according to the invention has previously been immobilized , of the antibodies contained in the serum of pigs infected by a pwd circovirus . the invention likewise relates to mono - or polyclonal antibodies or their fragments , or chimeric antibodies , characterized in that they are capable of specifically recognizing a polypeptide according to the invention . it will likewise be possible for the antibodies of the invention to be labeled in the same manner as described previously for the nucleic probes of the invention , such as a labeling of enzymatic , fluorescent or radioactive type . the invention is additionally directed at a procedure for the detection and / or identification of pwd circovirus , of porcine circovirus other than a pwd circovirus , or other than the pwd circovirus of type b , in a biological sample , characterized in that it comprises the following steps : a ) contacting of the biological sample ( biological tissue or fluid ) with a mono - or polyclonal antibody according to the invention ( under conditions allowing an immunological reaction between said antibodies and the polypeptides of pwd circovirus , of porcine circovirus other than a pwd circovirus , of porcine circovirus other than the pwd circovirus of type b , possibly present in the biological sample ); likewise within the scope of the invention is a kit or set for the detection and / or the identification of pwd circovirus , of porcine circovirus other than a pwd circovirus or of porcine circovirus other than the pwd circovirus of type b , characterized in that it comprises the following components : a polyclonal or monoclonal antibody according to the invention , if need be labeled ; if need be , a reagent for the formation of the medium favorable to the carrying out of the immunological reaction ; if need be , a reagent allowing the detection of the antigen - antibody complexes produced by the immunological reaction , this reagent likewise being able to carry a label , or being capable of being recognized in its turn by a labeled reagent , more particularly in the case where said monoclonal or polyclonal antibody is not labeled ; if need be , reagents for carrying out the lysis of cells of the sample tested . the present invention likewise relates to a procedure for the detection and / or the identification of pwd , of porcine circovirus other than a pwd circovirus or of porcine circovirus other than the pwd circovirus of type b , in a biological sample , characterized in that it employs a nucleotide sequence according to the invention . more particularly , the invention relates to a procedure for the detection and / or the identification of pwd circovirus , of porcine circovirus other than a pwd circovirus or of porcine circovirus other than the pwd circovirus of type b , in a biological sample , characterized in that it contains the following steps : a ) if need be , isolation of the dna from the biological sample to be analyzed ; b ) specific amplification of the dna of the sample with the aid of at least one primer , or a pair of primers , according to the invention ; these can be detected , for example , by the technique of molecular hybridization utilizing a nucleic probe according to the invention . this probe will advantageously be labeled with a nonradioactive ( cold probe ) or radioactive element . for the purposes of the present invention , “ dna of the biological sample ” or “ dna contained in the biological sample ” will be understood as meaning either the dna present in the biological sample considered , or possibly the cdna obtained after the action of an enzyme of reverse transcriptase type on the rna present in said biological sample . another aim of the present invention consists in a procedure according to the invention , characterized in that it comprises the following steps : a ) contacting of a nucleotide probe according to the invention with a biological sample , the dna contained in the biological sample having , if need be , previously been made accessible to hybridization under conditions allowing the hybridization of the probe with the dna of the sample ; b ) demonstration of the hybrid formed between the nucleotide probe and the dna of the biological sample . the present invention also relates to a procedure according to the invention , characterized in that it comprises the following steps : a ) contacting of a nucleotide probe immobilized on a support according to the invention with a biological sample , the dna of the sample having , if need be , previously been made accessible to hybridization , under conditions allowing the hybridization of the probe with the dna of the sample ; b ) contacting of the hybrid formed between the nucleotide probe immobilized on a support and the dna contained in the biological sample , if need be after elimination of the dna of the biological sample which has not hybridized with the probe , with a nucleotide probe labeled according to the invention ; according to an advantageous embodiment of the procedure for detection and / or identification defined previously , this is characterized in that , prior to step a ), the dna of the biological sample is first amplified with the aid of at least one primer according to the invention . the invention is additionally directed at a kit or set for the detection and / or the identification of pwd circovirus , of porcine circovirus other than the pwd circovirus or of porcine circovirus other than the pwd circovirus of type b , characterized in that it comprises the following elements : b ) if need be , the reagents necessary for the carrying out of a hybridization reaction ; c ) if need be , at least one primer according to the invention as well as the reagents necessary for an amplification reaction of the dna . the invention likewise relates to a kit or set for the detection and / or the identification of pwd circovirus , of porcine circovirus other than a pwd circovirus or of porcine circovirus other than the pwd circovirus of type b , characterized in that it comprises the following components : b ) an oligonucleotide probe , called a revealing probe , according to the invention , c ) if need be , at least one primer according to the invention , as well as the reagents necessary for an amplification reaction of the dna . the invention also relates to a kit or set for the detection and / or identification of pwd circovirus , of porcine circovirus other than a pwd circovirus or of porcine circovirus other than the pwd circovirus of type b , characterized in that it comprises the following elements : b ) if need be , the reagents necessary for carrying out a dna amplification reaction ; c ) if need be , a component allowing the sequence of the amplified fragment to be verified , more particularly an oligonucleotide probe according to the invention . the invention additionally relates to the use of a nucleotide sequence according to the invention , of a polypeptide according to the invention , of an antibody according to the invention , of a cell according to the invention , and / or of an animal transformed according to the invention , for the selection of an organic or inorganic compound capable of modulating , inducing or inhibiting the expression of genes , and / or of modifying the cellular replication of pwd circovirus or capable of inducing or of inhibiting the pathologies linked to an infection by a pwd circovirus . the invention likewise comprises a method of selection of compounds capable of binding to a polypeptide or one of its fragments according to the invention , capable of binding to a nucleotide sequence according to the invention , or capable of recognizing an antibody according to the invention , and / or capable of modulating , inducing or inhibiting the expression of genes , and / or of modifying the cellular replication of pwd circovirus or capable of inducing or inhibiting the pathologies linked to an infection by a pwd circovirus , characterized in that it comprises the following steps : a ) contacting of said compound with said polypeptide , said nucleotide sequence , or with a cell transformed according to the invention and / or administration of said compound to an animal transformed according to the invention ; b ) determination of the capacity of said compound to bind to said polypeptide or said nucleotide sequence , or to modulate , induce or inhibit the expression of genes , or to modulate the growth or the replication of pwd circovirus , or to induce or inhibit in said transformed animal the pathologies linked to an infection by pwd circovirus ( designated activity of said compound ). the compounds capable of being selected can be organic compounds such as polypeptides or carbohydrates or any other organic or inorganic compounds already known , or novel organic compounds elaborated by molecular modelling techniques and obtained by chemical or biochemical synthesis , these techniques being known to the person skilled in the art . it will be possible to use said selected compounds to modulate the cellular replication of pwd circovirus and thus to control infection by this virus , the methods allowing said modulations to be determined being well known to the person skilled in the art . this modulation can be carried out , for example , by an agent capable of binding to a protein and thus of inhibiting or of potentiating its biological activity , or capable of binding to an envelope protein of the external surface of said virus and of blocking the penetration of said virus into the host cell or of favoring the action of the immune system of the infected organism directed against said virus . this modulation can likewise be carried out by an agent capable of binding to a nucleotide sequence of a dna of said virus and of blocking , for example , the expression of a polypeptide whose biological or structural activity is necessary for the replication or for the proliferation of said virus host cells to host cells in the host animal . the invention relates to the compounds capable of being selected by a selection method according to the invention . the invention likewise relates to a pharmaceutical composition comprising a compound selected from the following compounds : c ) a vector , a viral particle or a cell transformed according to the invention ; e ) a compound capable of being selected by a selection method according to the invention ; possibly in combination with a pharmaceutically acceptable vehicle and , if need be , with one or more adjuvants of the appropriate immunity . the invention also relates to an immunogenic and / or vaccine composition , characterized in that it comprises a compound selected from the following compounds : c ) a vector or a viral particle according to the invention ; and in one embodiment , the vaccine composition according to the invention is characterized in that it comprises a mixture of at least two of said compounds a ), b ), c ) and d ) above and in that one of the two said compounds is related to the pwd circovirus of type a and the other is related to the pwd circovirus of type b . in another embodiment of the invention , the vaccine composition is characterized in that it comprises at least one compound a ), b ), c ), or d ) above which is related to pwd circovirus of type b . in still another embodiment , the vaccine composition is characterized in that it comprises at least one compound a ), b ), c ), or d ) above which is related to pwd circovirus of type b orf ′ 2 . a compound related to the pwd circovirus of type a or of type b is understood here as respectively designating a compound obtained from the genomic sequence of the pwd circovirus of type a or of type b . the invention is additionally aimed at an immunogenic and / or vaccine composition , characterized in that it comprises at least one of the following compounds : a nucleotide sequence seq id no . 23 , seq id no . 25 , or one of their fragments or homologues ; a polypeptide of sequence seq id no . 24 , seq id no . 26 , or one of their fragments , or a modification thereof ; a vector or a viral particle comprising a nucleotide sequence seq id no . 23 , seq id no . 25 , or one of their fragments or homologues ; a transformed cell capable of expressing a polypeptide of sequence seq id no . 24 , seq id no . 26 , or one of their fragments , or a modification thereof ; or a mixture of at least two of said compounds . the invention also comprises an immunogenic and / or vaccine composition according to the invention , characterized in that it comprises said mixture of at least two of said compounds as a combination product for simultaneous , separate or protracted use for the prevention or the treatment of infection by a pwd circovirus , especially of type b . in a preferred embodiment , the vaccine composition according to the invention comprises the mixture of the following compounds : a pcdna3 plasmid containing a nucleic acid of sequence seq id no . 23 ; a pcdna3 plasmid containing a nucleic acid of sequence seq id no . 25 ; a pcdna3 plasmid containing a nucleic acid coding for the gm - csf protein ; a recombinant baculovirus containing a nucleic acid of sequence seq id no . 23 ; a recombinant baculovirus containing a nucleic acid of sequence seq id no . 25 ; and if need be , an adjuvant of the appropriate immunity , especially the adjuvant aif ™. the invention is likewise directed at a pharmaceutical composition according to the invention , for the prevention or the treatment of an infection by a pwd circovirus . the invention is also directed at a pharmaceutical composition according to the invention for the prevention or the treatment of an infection by the pwd circovirus of type b . the invention likewise concerns the use of a composition according to the invention , for the preparation of a medicament intended for the prevention or the treatment of infection by a pwd circovirus , preferably by the pwd circovirus of type b . under another aspect , the invention relates to a vector , a viral particle or a cell according to the invention , for the treatment and / or the prevention of a disease by gene therapy . finally , the invention comprises the use of a vector , of a viral particle or of a cell according to the invention for the preparation of a medicament intended for the treatment and / or the prevention of a disease by gene therapy . the polypeptides of the invention entering into the immunogenic or vaccine compositions according to the invention can be selected by techniques known to the person skilled in the art such as , for example , depending on the capacity of said polypeptides to stimulate the t cells , which is translated , for example , by their proliferation or the secretion of interleukins , and which leads to the production of antibodies directed against said polypeptides . in pigs , as in mice , in which a weight dose of the vaccine composition comparable to the dose used in man is administered , the antibody reaction is tested by taking of the serum followed by a study of the formation of a complex between the antibodies present in the serum and the antigen of the vaccine composition , according to the usual techniques . the pharmaceutical compositions according to the invention will contain an effective quantity of the compounds of the invention , that is to say in sufficient quantity of said compound ( s ) allowing the desired effect to be obtained , such as , for example , the modulation of the cellular replication of pwd circovirus . the person skilled in the art will know how to determine this quantity , as a function , for example , of the age and of the weight of the individual to be treated , of the state of advancement of the pathology , of the possible secondary effects and by means of a test of evaluation of the effects obtained on a population range , these tests being known in these fields of application . according to the invention , said vaccine combinations will preferably be combined with a pharmaceutically acceptable vehicle and , if need be , with one or more adjuvants of the appropriate immunity . today , various types of vaccines are available for protecting animals or man against infectious diseases : attenuated living microorganisms ( m . bovis — bcg for tuberculosis ), inactivated microorganisms ( influenza virus ), acellular extracts ( bordetella pertussis for whooping cough ), recombined proteins ( surface antigen of the hepatitis b virus ), polysaccharides ( pneumococcal ). vaccines prepared from synthetic peptides or genetically modified microorganisms expressing heterologous antigens are in the course of experimentation . more recently still , recombined plasmid dnas carrying genes coding for protective antigens have been proposed as an alternative vaccine strategy . this type of vaccination is carried out with a particular plasmid originating from a plasmid of e . coli which does not replicate in vivo and which codes uniquely for the vaccinating protein . animals have been immunized by simply injecting the naked plasmid dna into the muscle . this technique leads to the expression of the vaccine protein in situ and to an immune response of cellular type ( ctl ) and of humoral type ( antibody ). this double induction of the immune response is one of the principal advantages of the vaccination technique with naked dna . the vaccine compositions comprising nucleotide sequences or vectors into which are inserted said sequences are especially described in the international application no . wo 90 / 11092 and likewise in the international application no . wo 95 / 11307 . the constitutive nucleotide sequence of the vaccine composition according to the invention can be injected into the host after having been coupled to compounds which favor the penetration of this polynucleotide into the interior of the cell or its transport to the cell nucleus . the resultant conjugates can be encapsulated in polymeric microparticles , as described in the international application no . wo 94 / 27238 ( medisorb technologies international ). according to another embodiment of the vaccine composition according to the invention , the nucleotide sequence , preferably a dna , is complexed with deae - dextran ( pagano et al ., 1967 ) or with nuclear proteins ( kaneda et al ., 1989 ), with lipids ( felgner et al ., 1987 ) or encapsulated in liposomes ( fraley et al ., 1980 ) or else introduced in the form of a gel facilitating its transfection into the cells ( midoux et al ., 1993 , pastore et al ., 1994 ). the polynucleotide or the vector according to the invention can also be in suspension in a buffer solution or be combined with liposomes . advantageously , such a vaccine will be prepared according to the technique described by tacson et al . or huygen et al . in 1996 or alternatively according to the technique described by davis et al . in the international application no . wo 95 / 11307 . such a vaccine can likewise be prepared in the form of a composition containing a vector according to the invention , placed under the control of regulation elements allowing its expression in man or animal . it will be possible , for example , to use , by way of in vivo expression vector of the polypeptide antigen of interest , the plasmid pcdna3 or the plasmid pcdna1 / neo , both marketed by invitrogen ( r & amp ; d systems , abingdon , united kingdom ). it is also possible to use the plasmid v1jns . tpa , described by shiver et al . in 1995 . such a vaccine will advantageously comprise , apart from the recombinant vector , a saline solution , for example a sodium chloride solution . pharmaceutically acceptable vehicle is understood as designating a compound or a combination of compounds entering into a pharmaceutical composition or vaccine which does not provoke secondary reactions and which allows , for example , the facilitation of the administration of the active compound , an increase in its duration of life and / or its efficacy in the body , an increase in its solubility in solution or alternatively an improvement in its conservation . these pharmaceutically acceptable vehicles are well known and will be adapted by the person skilled in the art as a function of the nature and of the mode of administration of the chosen active compound . as far as the vaccine formulations are concerned , these can comprise adjuvants of the appropriate immunity which are known to the person skilled in the art , such as , for example , aluminum hydroxide , a representative of the family of muramyl peptides such as one of the peptide derivatives of n - acetyl muramyl , a bacterial lysate , or alternatively freund &# 39 ; s incomplete adjuvant . these compounds can be administered by the systemic route , in particular by the intravenous route , by the intramuscular , intradermal or subcutaneous route , or by the oral route . in a more preferred manner , the vaccine composition comprising polypeptides according to the invention will be administered by the intramuscular route , through the food or by nebulization several times , staggered over time . their administration modes , dosages and optimum pharmaceutical forms can be determined according to the criteria generally taken into account in the establishment of a treatment adapted to an animal such as , for example , the age or the weight , the seriousness of its general condition , the tolerance to the treatment and the secondary effects noted . preferably , the vaccine of the present invention is administered in an amount that is protective against piglet weight loss disease . for example , in the case of a vaccine according to the present invention comprising a polypeptide encoded by a nucleotide sequence of the genome of pcv , or a homologue or fragment thereof , the polypeptide will be administered one time or several times , spread out over time , directly or by means of a transformed cell capable of expressing the polypeptide , in an amount of about 0 . 1 to 10 μg per kilogram weight of the animal , preferrably about 0 . 2 to about 5 μg / kg , more preferably about 0 . 5 to about 2 μg / kg for a dose . the present invention likewise relates to the use of nucleotide sequences of pwd circovirus according to the invention for the construction of autoreplicative retroviral vectors and the therapeutic applications of these , especially in the field of human gene therapy in vivo . the feasibility of gene therapy applied to man no longer needs to be demonstrated and this relates to numerous therapeutic applications like genetic diseases , infectious diseases and cancers . numerous documents of the prior art describe the means of employing gene therapy , especially through viral vectors . generally speaking , the vectors are obtained by deletion of at least some of the viral genes which are replaced by the genes of therapeutic interest . such vectors can be propagated in a complementation line which supplies in trans the deleted viral functions in order to generate a defective viral vector particle for replication but capable of infecting a host cell . to date , the retroviral vectors are amongst the most widely used and their mode of infection is widely described in the literature accessible to the person skilled in the art . the principle of gene therapy is to deliver a functional gene , called a gene of interest , of which the rna or the corresponding protein will produce the desired biochemical effect in the targeted cells or tissues . on the one hand , the insertion of genes allows the prolonged expression of complex and unstable molecules such as rnas or proteins which can be extremely difficult or even impossible to obtain or to administer directly . on the other hand , the controlled insertion of the desired gene into the interior of targeted specific cells allows the expression product to be regulated in defined tissues . for this , it is necessary to be able to insert the desired therapeutic gene into the interior of chosen cells and thus to have available a method of insertion capable of specifically targeting the cells or the tissues chosen . among the methods of insertion of genes , such as , for example , microinjection , especially the injection of naked plasmid dna ( derse , d . et al ., 1995 , and zhao , t . m . et al ., 1996 ), electroporation , homologous recombination , the use of viral particles , such as retroviruses , is widespread . however , applied in vivo , the gene transfer systems of recombinant retroviral type at the same time have a weak infectious power ( insufficient concentration of viral particles ) and a lack of specificity with regard to chosen target cells . the production of cell - specific viral vectors , having a tissue - specific tropism , and whose gene of interest can be translated adequately by the target cells , is realizable , for example , by fusing a specific ligand of the target host cells to the n - terminal part of a surface protein of the envelope of pwd circovirus . it is possible to mention , for example , the construction of retroviral particles having the cd4 molecule on the surface of the envelope so as to target the human cells infected by the hiv virus ( young , j . a . t . et al ., sciences 1990 , 250 , 1421 - 1423 ), viral particles having a peptide hormone fused to an envelope protein to specifically infect the cells expressing the corresponding receptor ( kasahara , n . et al ., sciences 1994 , 266 , 1373 - 1376 ) or else alternatively viral particles having a fused polypeptide capable of immobilizing on the receptor of the epidermal growth factor ( egf ) ( cosset , f . l . et al ., j . of virology 1995 , 69 , 10 , 6314 - 6322 ). in another approach , single - chain fragments of antibodies directed against surface antigens of the target cells are inserted by fusion with the n - terminal part of the envelope protein ( valsesia - wittman , s . et al ., j . of virology 1996 , 70 , 3 , 2059 - 2064 ; tearina chu , t . h . et al ., j . of virology 1997 , 71 , 1 , 720 - 725 ). for the purposes of the present invention , a gene of interest in use in the invention can be obtained from a eukaryotic or prokaryotic organism or from a virus by any conventional technique . it is , preferably , capable of producing an expression product having a therapeutic effect and it can be a product homologous to the cell host or , alternatively , heterologous . in the scope of the present invention , a gene of interest can code for an ( i ) intracellular or ( ii ) membrane product present on the surface of the host cell or ( iii ) secreted outside the host cell . it can therefore comprise appropriate additional elements such as , for example , a sequence coding for a secretion signal . these signals are known to the person skilled in the art . in accordance with the aims pursued by the present invention , a gene of interest can code for a protein corresponding to all or part of a native protein as found in nature . it can likewise be a chimeric protein , for example arising from the fusion of polypeptides of various origins or from a mutant having improved and / or modified biological properties . such a mutant can be obtained , by conventional biological techniques , by substitution , deletion and / or addition of one or more amino acid residues . it is very particularly preferred to employ a gene of therapeutic interest coding for an expression product capable of inhibiting or retarding the establishment and / or the development of a genetic or acquired disease . a vector according to the invention is in particular intended for the prevention or for the treatment of cystic fibrosis , of hemophilia a or b , of duchenne &# 39 ; s or becker &# 39 ; s myopathy , of cancer , of aids and of other bacteria or infectious diseases due to a pathogenic organism : virus , bacteria , parasite or prion . the genes of interest utilizable in the present invention are those which code , for example , for the following proteins : a cytokine and especially an interleukin , an interferon , a tissue necrosis factor and a growth factor and especially a hematopoietic growth factor ( g - csf , gm - csf ), a factor or cofactor involved in clotting and especially factor viii , von willebrand &# 39 ; s factor , antithrombin iii , protein c , thrombin and hirudin , an enzyme or an enzyme inhibitor such as the inhibitors of viral proteases , an expression product of a suicide gene such as thymidine kinase of the hsv virus ( herpesvirus ) of type 1 , an activator or an inhibitor of ion channels , a protein of which the absence , the modification or the deregulation of expression is responsible for a genetic disease , such as the cftr protein , dystrophin or minidystrophin , insulin , ada ( adenosine diaminose ), glucocerebrosidase and phenylhydroxylase , a protein capable of inhibiting the initiation or the progression of cancers , such as the expression products of tumor suppressor genes , for example the p53 and rb genes , a protein capable of stimulating an immune or an antibody response , and a protein capable of inhibiting a viral infection or its development , for example the antigenic epitopes of the virus in question or altered variants of viral proteins capable of entering into competition with the native viral proteins . the invention thus relates to the vectors characterized in that they comprise a nucleotide sequence of pwd circovirus according to the invention , and in that they additionally comprise a gene of interest . the present invention likewise relates to viral particles generated from said vector according to the invention . it additionally relates to methods for the preparation of viral particles according to the invention , characterized in that they employ a vector according to the invention , including viral pseudoparticles ( vlp , virus - like particles ). the invention likewise relates to animal cells transfected by a vector according to the invention . likewise comprised in the invention are animal cells , especially mammalian , infected by a viral particle according to the invention . the present invention likewise relates to a vector , a viral particle or a cell according to the invention , for the treatment and / or the prevention of a genetic disease or of an acquired disease such as cancer or an infectious disease . the invention is likewise directed at a pharmaceutical composition comprising , by way of therapeutic or prophylactic agent , a vector or a cell according to the invention , in combination with a vehicle acceptable from a pharmaceutical point of view . other characteristics and advantages of the invention appear in the examples and the figures . the invention is described in more detail in the following illustrative examples . although the examples may represent only selected embodiments of the invention , it should be understood that the following examples are illustrative and not limiting . cloning , sequencing and characterization of the pwd circovirus of type a ( pcva ) experimental reproduction of the infection and its syndrome ( cf . fig1 ). a first test was carried out with pigs from a very well - kept farm , but affected by piglet weight loss disease ( pwd ), likewise called fatal piglet wasting ( fpw ). tests carried out with spf ( specific pathogen - free ) pigs showed a transfer of contaminant ( s ) finding expression in a complex pathology combining hyperthermia , retardation of growth , diarrhea and conjunctivitis . the pdrs ( porcine dysgenic and respiratory syndrome ) virus , an infectious disease due to an arteriovirus ) was rapidly isolated from breeding pigs and contact pigs . it should have been possible to attribute all the clinical signs to the presence of the pdrs virus . however , two farm pigs presented signs of fpw without the pdrs virus being isolated . the histological analyses and blood formulas , however , showed that these pigs were suffering from an infectious process of viral origin . in a second test , 8 - week spf pigs were inoculated by the intratracheal route with organ homogenates of two farm pigs suffering from fpw . the inoculated pigs exhibited hyperthermia 8 to 9 days post - infection , then their growth was retarded . other spf pigs , placed in contact , had similar , attenuated signs 30 days after the initial experiment . no seroconversion with respect to a european or canadian strain of pdrs virus was recorded in these animals . a third test allowed the syndrome to be reproduced from samples taken from the pigs of the second test . the syndrome is reproduced under the experimental conditions . it is determined by at least one infectious agent , which is transmittable by direct contact . the clinical constants are a sometimes high hyperthermia ( greater than or equal to 41 . 5 ° c .) which develops 8 to 10 days after infection . retardation of the growth can be observed . the other signs are a reversal of the blood formula ( reversal of the lymphocyte / polynuclear ratio from 70 / 30 to 30 / 70 ) and frequent lesions on the ganglia , especially those draining the respiratory apparatus ( ganglionic hypertrophy , loss of structure with necrosis and infiltration by mononucleated or plurinucleated giant cells ). various cell supports including primary pig kidney cells or cell lines , pig testicle cells , monkey kidney cells , pig lymphocytes , pig alveolar macrophages and circulating blood monocytes were used to demonstrate the possible presence of a virus . no cytopathic effect was demonstrated in these cells . on the other hand , the use of a serum of a pig sick after experimental infection allowed an intracellular antigen to be revealed in the monocytes , the macrophages and approximately 10 % of pig kidney ( pk ) cells infected with organ homogenates . this indirect revealing was carried out kinetically at different culture times . it is evident from this that the antigen initially appears in the nucleus of the infected cells before spreading into the cytoplasm . the successive passages in cell culture did not allow the signal to be amplified . under electron microscopy on organ homogenates , spherical particles labeled specifically by the serum of sick pigs , infected under the experimental conditions , were visualized . the size of these particles is estimated at 20 nm . after two passages of these organ homogenates over pig lymphocytes and then three passages over pig kidney or testicle cells , a cytopathic effect developed and was amplified . an adenovirus was visualized in the electron microscope , which , under the experimental conditions , did not reproduce fpw ( only a hyperthermia peak was noted 24 to 48 hours after infection , and then nothing more ). it has been possible to demonstrate dna bands in certain samples of pigs infected under the experimental conditions and having exhibited signs of the disease ( results not shown ). a certain connection exists between the samples giving a positive result in cell culture and those having a dna band . at least two types of virus were demonstrated in the organ homogenates from pigs suffering from fpw . one is an adenovirus , but by itself alone it does not reproduce the disease . the other type of virus is a circovirus and is associated with fpw . this circovirus , of which two types have been isolated and sequenced , designated below pwd circovirus type a ( or pcva ) and pwd circovirus of type b ( or pcvb ) have mutations with respect to the known sequences of circovirus which are nonpathogenic for the pig . 3 . cloning and sequencing of the dna of the pwd circovirus of type a extraction of the replicative form ( rf ) dna , cleavage by the kpn i enzyme and amplification by a pair of primers flanking the kpn i restriction site . sequencing of the two strands at least twice by the sanger method . the nucleic sequence of the strand of (+) polarity of the genome of the pwd circovirus of type a ( or pcva ), strain fpw , is represented by the sequence seq id no . 1 in the list of sequences , the nucleic sequence of the strand of (−) polarity of the genome of the pwd circovirus of type a ( or pcva ) being represented by the nucleic sequence 3 ′→ 5 ′ of fig3 or by the sequence seq id no . 5 ( represented according to the orientation 5 ′→ 3 ′) in the list of sequences . the amino acid sequences seq id no . 10 , seq id no . 12 and seq id no . 14 of the list of sequences respectively represent the sequences of proteins encoded by the nucleic sequences of the 3 open reading frames seq id no . 9 ( orf1 ), corresponding to the rep protein , seq id no . 11 ( orf2 ) and seq id no . 13 ( orf3 ), determined from the sequence seq id no . 1 of the strand of (+) polarity or of the nucleic sequence seq id no . 5 of the strand of (−) polarity of the genome of the pwd circovirus of type a . 4 . comparison of the nucleotide sequences and amino acids of the pwd circovirus of type a ( or associated with pwd ) which are obtained with the corresponding sequences of meehan and mankertz circoviruses of porcine cell lines sequences of oligonucleotides used as primers or probes in the detection and / or identification procedures seq id no . 46 primer pcv 5 : 5 ′ gtg tgc tcg aca ttg gtg tg 3 ′; seq id no . 47 primer pcv 10 : 5 ′ tgg aat gtt aac gag ctg ag 3 ′; seq id no . 46 primer pcf 5 : 5 ′ gtg tgc tcg aca ttg gtg tg 3 ′; seq id no . 52 primer mee 1 : 5 ′ tgg aat gtt aac tac ctc aa 3 ′; the pairs of primers used are those described , for example , in the paragraphs 1 and 2 above ; seq id no . 46 primer pcv 5 : 5 ′ gtg tgc tcg aca ttg gtg tg 3 ′; seq id no . 48 primer pcv 6 : 5 ′ ctc gca gcc atc ttg gaa tg 3 ′; nar dimer : seq id no . 49 primer ks 620 : 5 ′ cgc gcg taa tac gac tca ct 3 ′; seq id no . 46 primer pcv 5 : 5 ′ gtg tgc tcg aca ttg gtg tg 3 ′; kpn dimer : seq id no . 49 primer ks 620 : 5 ′ cgc gcg taa tac gac tca ct 3 ′; seq id no . 48 primer pcv 6 : 5 ′ ctc gca gcc atc ttg gaa tg 3 ′; the pairs of primers used are those described , for example , in paragraphs 4 and 5 above . the procedures using the pairs or primers described in paragraphs 4 and 5 are of particular interest for differentially detecting the circular monomeric forms of specific replicative forms of the virion or of the dna in replication and the dimeric forms found in the so - called in - tandem molecular constructs . the in - tandem constructs of the viral genome ( dimers ) such as the constructs used for the preparation of the pbs ks + tandem pcv kpn i vector , deposited at the cncm under the number i - 1891 , 3 jul . 1997 ( e . coli transformed by said vector ) are very interesting for their use in methods of production in sufficient quantity of an inoculum formed of dna , intended for the virus production , this in the absence of a satisfactory virus production protocol in a cell system . these said methods of production using these in - tandem constructs of the viral genome will allow the virulence factors to be studied by mutation and by way of consequence will be able to be used for the production of a collection of viruses carrying the mutations indicated in the construction of vectors which will have the appropriate tropism and virulence . these vectors with autoreplicative structure have the sought gene transfer properties , especially for their applications in gene therapy , and in vaccinology . the results were obtained using a specific antiserum of the pwd circovirus produced during test 1 ( cf . fig1 ). the analyses were carried out on cell extracts of sf9 cells obtained after infection by the recombinant baculovirus pcv orf1 . the culture of sf9 cells was carried out in a 25 cm 2 petri dish according to the standard culture methods for these cells . after centrifugation , the cell pellets are taken up with 300 μl of pbs buffer ( phosphate saline buffer ). the electrophoresis is carried out on the cell extracts of sf9 cells obtained previously on 5 samples ( cf . table 1 below ) under the following conditions : % polyacrylamide gel : 8 %; conditions : denaturing 10 ml of pwd anticircovirus antibody of type a are added diluted to 1 / 100 , then the reaction mixture is incubated for one night at 4 ° c . three washes of 10 min in tbs 1 × are carried out . 10 ml of pig rabbit p164 antibody anti - immunoglobulins , coupled to peroxidase ( dakopath ) are added diluted to 1 / 100 , then the reaction medium is incubated for 3 hours at 37 ° c . three washes of 10 min in tbs 1 × are carried out . the substrate 4 - chloro - 1 - naphthol in the presence of oxygenated water is used for visualization . kinetics of appearance of antibodies specific for the rep recombinant protein of the pwd circovirus of type a expressed in baculovirus after infection of pigs by the pwd circovirus of type a ( test 4 , cf . fig1 ) after infection of the pigs , a sample of serum of each of the infected pigs is taken at different periods expressed in the table by the date of taking ( carried out here in the same year ) and is then analyzed by western blot . the visualization of the specific antibodies is carried out in the manner described previously . the techniques used for cloning , sequencing and characterization of the type b pwd circovirus ( pcvb ) are those used in example 1 above for the type a pwd circovirus ( pcva ). the nucleic sequence of the strand of (+) polarity of the genome of the pwd circovirus of type b ( or pcvb ) is represented by the sequence seq id no . 15 in the sequence listing , the nucleic sequence of the strand of (−) polarity of the genome of the pwd circovirus of type b ( or pcvb ) being represented by the nucleic sequence 3 ′→ 5 ′ of fig8 or by the sequence seq id no . 19 ( represented according to the orientation 5 ′→ 3 ′) in the sequence listing . the amino acid sequences seq id no . 24 , seq id no . 26 and seq id no . 28 of the sequence listing respectively represent the sequences of the proteins encoded by the nucleic sequences of the 3 open reading frames seq id no . 23 ( orf ′ 1 ), corresponding to the rep protein , seq id no . 25 ( orf ′ 2 ) and seq id no . 27 ( orf ′ 3 ), determined from the sequence seq id no . 15 of the strand of (+) polarity or from the nucleic sequence seq id no . 19 of the strand of (−) polarity of the genome of the pwd circovirus of type b . comparative analysis of nucleotide sequences ( orf1 , orf2 and genomic ) and amino acid sequences encoded by the orf1 and the orf2 of the pwd circoviruses of type a ( pcva ) and of type b ( pcvb ) the results expressed in % of homology are shown in tables 3 and 4 below . the objective is to take breeding animals at the start of disease and to place them under experimental conditions to follow the progression of the pathology and describe all the clinical signs thereof . this first test was carried out on 3 breeding pigs aged 10 weeks of which 2 were already ill ( suffering from wasting ), and on 3 other pigs aged 13 weeks , not having signs of disease . the clinical observation was spread over a period of 37 days . two pigs of 10 weeks wasted rapidly ( pigs 1 and 2 , fig9 ) and had to be painlessly killed 5 and 6 days after their arrival . a single pig exhibited hyperthermia over 5 days and diarrhea . two other pigs exhibited dyspnea and cough , of which one additionally had hyperthermia , greater than 41 ° c ., for the two first days of its stay . another pig had retarded growth in the second week ( pig 6 , fig9 ), without any other clinical sign being recorded . on the lesional level , 5 pigs out of 6 exhibited macroscopic lesions of gray pneumonia , the sixth exhibited cicatricial lesions on the lung . b ) test no . 2 : reproduction of the disease from inocula prepared in farm pigs . the two sick pigs in test 1 served to prepare inocula which were tested in test 2 on specific - pathogen - free ( spf ) pigs . the spf pigs were aged 9 weeks at the time of inoculation . the clinical and lesional results are shown in table 5 . **** the percentage corresponds to the number of temperature recordings greater than 40 ° c . divided by the total number of temperature recordings in the week on all of the pigs . in this test , there was no wasting , at the very most a retardation of the growth in the second , third or fourth week after infection . these data illustrate that certain breeding conditions probably favor the expression of the disease . c ) tests no . 3 to no . 7 : reproduction of the experimental tests the increase in the number of the experimental tests on pigs had the mastering and better characterization of the experimental model as an objective . all of the results are presented in table 5 . under the experimental conditions , pwd is thus characterized by a long incubation , of 8 to 14 days , true hyperthermia over 2 to 8 days , a decrease in food consumption and a retardation of the increase in weight on the second , third or fourth week post - infection . the lesional table associated with this clinical expression includes , in the main , ganglionic hypertrophy and lesions of pneumonia . the perfection of this experimental model allows the direct etiological role of the pwd circovirus in the disease to be indisputably demonstrated . in addition , this model is an indispensable tool for the understanding of pathogenic mechanisms and the study of future vaccine candidates . demonstration of the vaccine composition protective efficacy produced from nucleic fragments of pwd circovirus sequence piglets having the pwd disease , reproduced under experimental conditions described in paragraph c ) of example 4 , were used in a protocol for evaluating the vaccine composition efficacy , comprising nucleic fragments of pwd circovirus sequence . these plasmids are plasmids which do not carry a pwd circovirus nucleic acid insert and are used as a negative control plasmid . the pcdna3orf1 + and pcdna3orf2 + plasmids are plasmids which carry a nucleic acid insert of the sequence of the pwd circovirus of type b , respectively an insert comprising the nucleic acid fragment seq id no . 23 ( orf ′ 1 ) coding for the rep protein of sequence seq id no . 24 and an insert comprising the nucleic acid fragment seq id no . 25 ( orf ′ 2 ) coding for the protein of sequence seq id no . 26 , probably corresponding to the capsid protein , these nucleic constructs comprising the atg initiation codon of the coding sequence of the corresponding protein . gm - csf ( granulocyte / macrophage colony stimulating factor ) is a cytokine which occurs in the development , the maturation and the activation of macrophages , granulocytes and dendritic cells which present an antigen . the beneficial contribution of the gm - csf in vaccination is considered to be a cellular activation with , especially , the recruitment and the differentiation of cells which present an antigen . this pcdna3 - gmcsf + plasmid carries a nucleic acid insert coding for the granulocyte / macrophage colony stimulation factor , the gm - csf protein . the gene coding for this gm - csf protein was cloned and sequenced by inumaru et al . ( immunol . cell biol ., 1995 , 73 ( 5 ), 474 - 476 ). the pcdna3 - gmcsf + plasmid was obtained by dr . b . charley of inra of jouy - en - josas ( 78 , france ). the so - called orf − baculoviruses are viruses not carrying any insert comprising a nucleic acid fragment capable of expressing a pwd circovirus protein . the so - called orf1 + ( bac orf1 +) or orf2 + ( bac orf2 +) baculoviruses are recombinant baculoviruses respectively carrying an insert comprising a nucleic acid fragment seq id no . 23 ( orf ′ 1 ) and an insert comprising the nucleic acid fragment seq id no . 25 ( orf ′ 2 ). the adjuvant supplied by the seppic company , a subsidiary of air liquide , is the adjuvant corresponding to the reference aif seppic . weaned piglets aged 3 weeks are divided into four batches a , b , c and d each comprising 8 piglets . batches a , b and c , aged 3 weeks , each receive a first injection ( injection m1 ) of 1 ml containing 200 micrograms of plasmids ( naked dna ) in pbs , ph : 7 . 2 , by the intramuscular route for each of the plasmids mentioned below for each batch , then , at the age of 5 weeks , a second injection ( injection m2 ) comprising these same plasmids . a third injection is carried out simultaneously on the other side of the neck . this third injection comprises 1 ml of a suspension containing 5 . 10 6 cells infected by recombinant baculoviruses and 1 ml of aif seppic adjuvant . pcdna3orf1 − plasmid , pcdna3orf2 − plasmid and gmcsf + plasmid ; cells transformed by baculoviruses not containing any nucleic acid insert coding for a pwd circovirus protein ; aif seppic adjuvant . pcdna3orf1 − plasmid , pcdna3orf2 − plasmid and gmcsf + plasmid ; cells transformed by baculoviruses not containing any nucleic acid insert coding for a pwd circovirus protein ; aif seppic adjuvant . pcdna3orf1 + plasmid , pcdna3orf2 + plasmid and gmcsf + plasmid ; cells transformed by bac orf1 + and bac orf2 + recombinant baculoviruses capable of respectively expressing the rep protein of sequence seq id no . 24 and the protein of sequence seq id no . 26 of the pwd circovirus of type b . the batches of piglets b , c and d are infected ( tested ) at the age of 6 weeks although batch a is not subjected to the test . counting of coughing / sneezing : 15 minutes / batch / day ; consistency of fecal matter : every day ; regular recordings : weekly taking of blood , weighing ; weighing of food refuse : 3 times per week ; calculation of the daily mean gain in weight ( dmg ); the daily mean gains were calculated for each of the batches over a period of 28 days following testing ( cf . fig1 ), an intermediate calculation of the dmg was likewise carried out for each of the batches over the first and second periods of 14 days . the results obtained are reported below in table 6 . the measurement of hyperthermia , of greater than 41 ° c . ( cf . fig1 ) and greater than 40 . 2 ° c ., was carried out for each of the batches over a total period of 28 days following testing . the results obtained , corresponding to the ratio expressed as a percentage between the number of recordings of heat of greater than 41 ° c . ( or greater than 40 . 2 ° c .) and the total number of recordings of heat carried out on all of the pigs per one - week period are reported below in tables 7 and 8 , respectively for the hyperthermia measurements of greater than 41 ° c . and greater than 40 . 2 ° c . the recordings carried out clearly show that the animals which received the three injections of a vaccine composition comprising nucleic acid fragments of pwd circovirus according to the invention and / or capable of expressing recombinant proteins of pwd circovirus , in particular of type b , did not exhibit hyperthermia ( cf . fig1 ). these animals additionally did not experience a decline in their growth , the dmgs being comparable to those of uninfected control animals ( cf . fig9 ). they did not exhibit any particular clinical sign . these results demonstrate the efficacious protection of the piglets against infection with a pwd circovirus of the invention , the primary agent responsible for pwd or fpw , provided by a vaccine composition prepared from a nucleic acid fragment of the nucleic sequence of pwd circovirus according to the invention , in particular of type b , and / or from recombinant proteins encoded by these nucleic acid fragments . these results in particular show that the proteins encoded by the orf1 and orf2 of pwd circovirus according to the invention are immunogenic proteins inducing an efficacious protective response for the prevention of infection by a pwd circovirus . serological diagnosis of pwd circovirus by immunodetermination using recombinant proteins or synthetic peptides of pwd circovirus the identification and the sequencing of porcine pwd circovirus allow recombinant proteins of pwd circovirus to be produced by the techniques of genetic recombination well known to the person skilled in the art . by these techniques , recombinant proteins encoded , in particular , by the orf ′ 2 of the pwd circovirus , type b , were expressed by transformed sf9 insect cells and then isolated . these recombinant proteins encoded by the orf ′ 2 are extracted , after culture of the transformed sf9 cells , by thermal cell lysis by means of 3 cycles of freezing / thawing to − 70 ° c ./+ 37 ° c . healthy sf9 cells or nontransformed control sf9 cells are also lyzed . these two antigenic fractions originating from nontransformed control sf9 cells and sf9 cells expressing the orf ′ 2 are precipitated at 4 ° c . by a 60 % plus or minus 5 % saturated ammonium sulfate solution . determination of total proteins is carried out with the aid of the biorad kit . 500 ng of control sf9 proteins and of semipurified sf9 proteins expressing the orf ′ 2 , in solution in 0 . 05 m bicarbonate buffer ph 9 . 6 , are passively adsorbed at the bottom of 3 different cupules of a nunc maxisorp microplate by incubation for one night at + 4 ° c . the reactivity of pig sera with respect to each of these antigenic fractions is evaluated by an indirect elisa reaction of which the experimental protocol is detailed below : saturation step : 200 μl / cupule of pbs1x / 3 % semi - skimmed milk , 1 h 30 incubation at 37 ° c . washing : 200 μl / cupule of pbs1x / tween 20 : 0 . 05 %, 3 rapid washes . serum incubation step : 100 μl / cupule of serum diluted to 1 / 100 in pbs1x / semi - skimmed milk , 1 %/ tween 20 : 0 . 05 %, 1 h incubation at 37 ° c . washing : 200 μl / cupule of pbs1x / tween 20 : 0 . 05 %, 2 rapid washes followed by 2 washes of 5 min . conjugate incubation step : 50 μl / cupule of rabbit anti - pig conjugate diluted to 1 / 1000 in pbs1x / semi - skimmed milk , 1 %/ tween 20 : 0 . 05 %, 1 h incubation at 37 ° c . washing : 200 μl / cupule of pbs 1x / tween 20 : 0 . 05 %, 2 rapid washes followed by 2 washes of 5 min . visualization step : 100 μl / cupule of opd substrate / citrate buffer / h 2 o 2 , 15 min incubation at 37 ° c . stopping of reaction : 50 μl / cupule of 1 n h 2 so 4 . reading in a spectrophotometer at 490 nm . the results are expressed in optical density measured in a spectrophotometer at 490 nm during analysis by elisa of the reactivity of pig sera which are or are not inoculated with the type b pwd circovirus according to the protocol indicated above . the epitopic mapping of the proteins encoded , for example , by the nucleic sequences orf1 and orf2 of the two types of pwd circovirus ( types a and b ) additionally allowed immunogenic circoviral epitopes to be identified on the proteins encoded by the nucleic sequences orf ′ 1 and orf ′ 2 as well as the specific epitopes of the protein encoded by the nucleic sequence orf ′ 2 of the type b pwd circovirus . four specific epitopes of the type b pwd circovirus and one epitope common to the two types of pwd circovirus situated on the protein encoded by the nucleic sequence orf ′ 2 were synthesized in peptide form . the equivalent peptides in the circovirus of type a were likewise synthesized . all these peptides were evaluated as diagnostic antigens within the context of carrying out a serological test . +/−, +, ++, +++. increasing intensities of the reactivities observed in spot peptides on a nitrocellulose membrane . the porcine sera tested are from animals experimentally infected with the circovirus of type b within the animal houses of the cneva . samples are taken from the animals before inoculation on d0 and 42 days or 54 days after inoculation , on d42 , d54 . the proteins encoded by the orf2 of the porcine circoviruses of type a and b were chosen for this study . for each of the orf2s ( types a and b ), 56 peptides of 15 amino acids which overlap every 4 amino acids were synthesized , thus covering the whole of the protein ( cf . table 11 below ). these peptides were synthesized according to the “ spot ” method which consists in simultaneous synthesis of a large number of peptides on a cellulose solid support , each site of synthesis of a peptide constituting a spot ( synt : em , nimes ). this method involves orientation of the peptides on the plate , these being fixed covalently by the carboxy - terminal end . a spot represents approximately 50 nmol of peptide . the reference of the spots and corresponding peptide sequences is given in table 11 . these membranes were used for immunoreactivity tests with respect to serum of spf pigs which were or were not infected experimentally with the type b pwd circoviral strain as well as with respect to sera of infected pigs from conventional farms ( conventional farms 1 or 2 ). this study allowed specific immunoreactive peptides of the circovirus of type b corresponding to the spots no . 121 , no . 132 , no . 133 and no . 152 ( respectively of amino acid sequences seq id no . 29 , seq id no . 30 , seq id no . 31 and seq id no . 32 ) to be demonstrated . an illustration is shown in fig1 where the membranes are visualized with an infected pig serum coming from a conventional farm . nonspecific immunoreactive peptides of type [ lacuna ] were likewise demonstrated , among which we shall keep the peptide no . 146 seq id no . 123 which is strongly immunogenic . a comparison between the peptide sequences of circoviruses of type a and b ( fig1 ) indicates a divergence ranging from 20 to 60 % for the specific immunoreactive peptides of the type b , and a weaker divergence ( 13 %) between the nonspecific peptides . protection of swine from post - weaning multisystemic wasting syndrome ( pmws ) conferred by procine circovirus typeb ( pcv - b ) orf ′ 2 protein the orf ′ 1 - encoded protein ( rep ) and orf ′ 2 - encoded putative capsid protein of pcv - b were expressed , either in insect cells by recombinant baculovirus vectors , or in mammalian cell lines by transfection with plasmidic expression vectors . these two circovirus - derived proteins were detectable in both expression system . as evaluated by weight gains , hyperthermia and absence of lesions following challenge , the pigs were protected against a virulent circovirus challenge after one first dna immunization with plasmids directing orf ′ 2 protein and gm - csf expression and a second injection , 15 days later , with the same plasmid preparation plus the orf ′ 2 recombinant protein . a lower level of protection was observed when the pigs were vaccinated with orf ′ 1 protein , as opposed to pigs vaccinated with orf ′ 2 protein . eight 3 week - old spf pigs were inoculated intratracheally ( 5 ml ) and intramuscularly ( 1 ml ). pcv - b orf ′ 1 and orf ′ 2 genes , isolated from pcv - b challenge strain , have been cloned into vector plasmid pcdna3 . 1 . all constructs have been validated through a partial sequencing of the pcv - b genes in the final plasmids and expression control by immunoperoxidase on pk15 cells respectively transfected with each plasmid , using swine polyclonal antibodies . plasmid encoding gm - csf has been co - administered . orf ′ 1 and orf ′ 2 proteins were expressed under polyhedrin promoter control . recombinant proteins were detected by western - blot using swine polyclonal antibodies . four groups of 7 pigs were vaccinated intramuscularly at day 0 ( do ), two weeks later , they received the same plasmid preparation plus the recombinant baculovirus . all groups of pigs were housed in isolated experimental units with air filtration and low air pressure . clinical observations and rectal temperatures were recorded every day . the pigs were weighed weekly . expression of pcv - b orf ′ 2 or pcv - b orf ′ 1 in swine resulted in a significantly enhanced level of protection as evaluated by weight evolution and body temperature evolution following challenge with pcv - b circovirus . these results are summarized in fig1 and 15 . the invention described herein may be embodied in other specific forms without departing from the spirit or essential characteristics thereof . the specific embodiments previously described are therefore to be considered as illustrative of , and not limiting , the scope of the invention . additionally , the disclosure of all publications and patent applications cited above and below , including international patent application no . pct / fr98 / 02634 , filed dec . 4 , 1998 , and published as international publication no . wo 99 / 29871 on jun . 17 , 1999 , are expressly incorporated herein by reference in their entireties to the same extent as if each were incorporated by reference individually . boulton , l . h . et al ., 1997 , j . gen . virol ., 78 ( pt 6 ), 1265 - 1270 . buckholz , r . g ., 1993 , yeast systems for the expression of heterologous gene products . curr . burg , j . l . et al ., 1996 , mol . and cell . probes , 10 : 257 - 271 . chu , p . w . g . et al ., 1993 , virus research , 27 : 161 - 171 . daft , b . et al ., 1996 , american association of veterinary laboratory diagnosticians , 32 . dulac , g . c . et al ., 1989 , can . j . vet . res ., 53 : 431 - 433 . edwards , c . p ., and aruffo , a ., 1993 , current applications of cos cell based transient expression systems . curr . op . biotechnology 4 : 558 - 563 . erlich , h . a ., 1989 , in pcr technology . principles and applications for dna amplification . new york : stockton press . fontes , e . p . b . et al ., 1994 , j . biol . chem ., vol . 269 , no . 11 : 8459 - 8465 . harding , r . m . et al ., 1993 , journal of general virology , 74 : 323 - 328 . harding , j . c . and clark , e . g ., 1997 , swine health and production , vol . 5 , no . 5 : 201 - 203 . heyraud - nitschke , f . et al ., 1995 , nucleic acids research , vol . 23 , no . 6 . houben - weyl , 1974 , in methode der organischen chemie , e . wunsch ed ., volume 15 - 1 and 15 - ii , thieme , stuttgart . innis , m . a . et al ., 1990 , in pcr protocols . a guide to methods and applications , san diego , academic press . lazarowitz , s . g . et al ., 1989 , the embo journal , vol . 8 no . 4 : 1023 - 1032 . luckow , v . a ., 1993 , baculovirus systems for the expression of human gene products . curr . op . biotechnology 4 : 564 - 572 . meehan , b . m . et al ., 1997 , j . gen . virol . 78 : 221 - 227 . miele , e . a . et al ., 1983 , j . mol . biol ., 171 : 281 - 295 . murphy , f . a . et al ., 1995 , sixth report of the international committee on taxonomy of viruses . springer - verlag wien new york . nayar , g . p . et al ., 1997 , can . vet . j . 38 ( 6 ): 385 - 386 . olins , p . o ., and lee , s . c ., 1993 , recent advances in heterologous gene expression in e . coli . rolfs , a . et al ., 1991 , in pcr topics . usage of polymerase chain reaction in genetic and infectious disease . berlin : springer - verlag . sambrook , j . et al ., 1989 , in molecular cloning : a laboratory manual . cold spring harbor , n . y . : cold spring harbor laboratory press . segev d ., 1992 , in “ non - radioactive labeling and detection of biomolecules ”. kessler c . springer verlag , berlin , new - york : 197 - 205 . shiver , j . w ., 1995 , in vaccines 1995 , eds chanock , r . m . brown , f . ginsberg , h . s . & amp ; norrby , e ., pp . 95 - 98 , cold spring harbor laboratory press , cold spring harbor , n . y . tischer , i . et al ., 1988 , zentralbl bakteriol mikrobiol hyg [ a ] 270 : 280 - 287 . white , b . a . et al ., 1997 , methods in molecular biology , 67 , humana press , towota . zhao , t . m . et al ., 1996 , proc . natl . acad . sci ., usa 93 ( 13 ): 6653 - 6648 . this application contains a sequence listing submitted in accordance with 37 cfr 1 . 52 ( e ), compact discs containing two copies of the sequence listing in lieu of a paper copy , said disc copies created on jul . 18 , 2006 , each file containing the identical sequence listing 159 kb file ( both named “ 09514245seq . txt ”) which sequence listing is hereby incorporated into the present specification .