it is found in countries and regions with inadequate sanitary infrastructure and insufficient health education .
the life cycle of the parasite includes the adult stage , the egg , and the larval stage ( cysticercus ) . when a person ingests raw or semi - cooked pork meat with cysticerci , the scolex evaginates and attaches with its double row of 22 to 32 hooks and its 4 suckers to the mucosa in the upper third section of the small intestine , which is the duodenum - jejunum , and in 3 - 4 months transforms into a fully developed adult tapeworm .
t. solium tapeworms measure 1 - 5 m long , and the scolex is followed by the neck , from which the strobila is formed , resembling a ribbon formed by 700 to 1,000 immature , mature , and gravid proglottids .
the immature proglottids have not yet developed sexual organs while the gravid proglottids resemble sacs full of eggs .
tapeworms are hermaphroditic organisms because each mature segment contains 350 to 600 testes and 3 ovary lobes .
gravid proglottids are released with feces , starting at 3 - 5 months after infection , and each proglottid contains between 50,000 and 60,000 eggs , located inside the multilobulated uterus . as proglottids are located farther away from the scolex they become bigger ; mature proglottids measure 2.1 to 2.5 mm long and 2.8 to 3.5 mm wide , while gravid segments measure 3.1 to 10 mm long and 3.8 to 8.7 mm wide .
they range in size from 26 to 34 m while cysticerci and adult worms are macroscopic and have a similar scolex that measures 0.6 to 1.0 mm .
eggs are conformed by the oncoshpere , or hexacanth embryo , and the embryophore that surrounds it . when swine ingest eggs , bile and enzymes disaggregate the embryophoric blocks and digest the oncospheral membrane ; in this way the oncosphere , with the aid of its hooks and enzymes , can cross the mucosa and circulate until it transforms into the larval stage .
cysticerci establish primarily in the skeletal and cardiac muscles , as well as in the brain of pigs , a process that takes approximately 3 months .
they remain viable for at least 1 year , when pigs are usually sent to slaughter . in humans ,
the former is a small , spherical or oval , white or yellow , vesicle that measures between 0.5 and 1.5 cm and has a translucent bladder wall , through which the scolex can be seen as a small solid eccentric granule .
this type of cysticerci is generally separated from the host tissue by a thin collagenous capsule , within which it remains alive .
the racemose cysticercus appears in the human brain either as a large , round , or lobulated bladder circumscribed by a delicate wall , or resembles a cluster of grapes , and measures up to 10 or even 20 cm and may contain 60 ml fluid .
interestingly , the scolex can not be seen , and in some cases only detailed histological studies reveal its remains .
cellulose type cysticerci are conformed by 2 chambers ; the inner one contains the scolex and the spiral canal and is surrounded by the outer compartment that contains the vesicular fluid , usually less than 0.5 ml .
when a person ingests a living cysticercus , the first event that takes place is the widening of the pore of the bladder wall for the scolex and neck to emerge , leaving the bladder wall and vesicular fluid to disintegrate in the digestive tract .
the domestic pig is the intermediate host because it harbors the cysticercus ; however , humans can acquire cysticercosis after accidentally ingesting t. solium eggs .
cysticerci in humans develop mainly in the central nervous system , eyes , striated and heart muscles , and subcutaneous tissues . in the brain
clinical manifestations are pleomorphic , and depend on the location , number , and stages of the lesions as well as characteristics of the immune response of the host .
, parasites can be palpated when superficial , or seen in x - rays as white dots or nodules , but generally they do not interfere with the muscle function , except in massive infections , when they cause muscle pseudo - hypertrophy with intense inflammation and pain .
, parasites are found in the subretinal space , close to the macula , vitreous fluid , or anterior chamber .
inflammation may cause blindness or decreased vision secondary to proliferative vitreo - retinopathy and retinal detachment .
although some books state that tapeworms can survive for about 25 years in the human intestine , recent experience indicates that t. solium remains only for around 1 year releasing along this time a few gravid proglottids in feces 2 - 3 times a week .
interestingly , the prevalence of taeniosis among patients with neurocysticercosis ( ncc ) is higher than previously reported .
in addition , a clear association between the presence of taeniosis and the severity of ncc has been reported , since most massive cerebral infections ( with more than 100 cysticerci ) were present in patients who harbored the adult tapeworm in the intestine .
therefore , the perception that tapeworms are silent guests , causing no harm to humans , is erroneous and tapeworm carriers should be regarded as potential sources of contagion to themselves and to those living in their close environment .
taenia asiatica differs from taenia saginata and t. solium in 4 aspects ; 1 ) the scolex has 2 rows of rudimentary hooklets , which is considered as a wart - like formation .
2 ) the number of the lateral branches of the uterus is different and allows identifying if the proglottids belong to t. solium ( 7 - 11 branches ) , t. saginata ( 14 - 32 branches ) , or t. asiatica ( 12 - 26 branches ) .
3 ) t. asiatica cysticerci in pigs are not found in muscles , they can be recovered from the liver , omentum , serosa , and lung .
between 1940 and 1970 , necropsy reports in mexico indicated that around 2% of adults had ncc , and between 50 and 80% of them had no symptoms . in 1972 , when i started my ph.d .
project , no computed tomography or magnetic resonance existed , and the only diagnostic procedure was using the cerebrospinal fluid , where antibodies by complement fixation and increase of eosinophils by differential count of blood cells , were the only methods to suggest cysticercosis in patients with neurologic symptoms such as convulsive crisis or hydrocephalus . therefore , along the next 20 years , immunoelectrophoresis , enzyme immunoassays , including elisa , and western blot were standardized with the aim of defining the real magnitude of t. solium in mexico by detecting specific anti - cysticercus antibodies in serum [ 7,9 - 13 ] .
immunoelectrophoresis was the first technique used in communities ; 1,610 samples obtained from 9 communities , mostly rural , in the state of chiapas were analyzed .
interestingly , in spite of the low sensitivity of immunoelectrophoresis ( 50% ) , its high specificity ( 100% because practically no echinococcosis is found in mexico ) allowed to identify a clear correlation .
communities with less than 4,000 inhabitants had 1 - 8% seropositivity , while populations with up to 35,000 citizens had 1% or less antibody frequency ; indicating that the parasite was more frequent in small , and thus less developed , towns .
afterwards , a study performed in 20,000 samples from a national survey , we were able to identify by immunoelectrophoresis a central area in mexico in which people had between 0.6 and 1% of anti - cysticercus antibodies ; remarkably , this geographic area , called " el bajio " is the most important pig breeding area in mexico for national consumption of pork meat .
a few years later in a small field practice for a group of epidemiology students , we identified the main risk factor for acquiring cysticercosis ; the tapeworm carrier , probably my main contribution to science .
this was recognized because there were " clusters " in the community ( 125 inhabitants ) where people with convulsive crisis and/or antibodies by elisa and pigs with cysticerci in the tongue lived close to a tapeworm carrier .
a survey was performed in a soldier camp in mexico city , blood and fecal samples from 1,000 militaries and their families were analyzed for t. solium serum elisa antibodies , copro - antigen elisa , and coproparasitoscopic detection of eggs .
demographic results were gathered in relation to positivity to any assay ; 86.7% of family members of positive soldiers ate in street food stores , as compared to 62.5% of family members of negative soldiers , while having a history of proglottid release was 12% vs 3.7% in the same family groups .
probably the study that was better known around the world , but certainly was not the first one , was that with the 4 families of orthodox jews that along 2 years each had a member that had convulsive crisis , which was confirmed at the center for disease control , atlanta , usa as due to ncc .
peter schantz to identify the risk factor , because being orthodox they did not want to know anything about " the pig tapeworm " .
he found out that they spent the previous vacation together and took with them a maid from mexico , and obtained the data from the maid ; we fetched her in the state of puebla and identified that she had a tapeworm , her brother and son had ncc ; also 7 other asymptomatic members from the jewish families were antibody positive by western blot .
thus , 1 tapeworm carrier in the household , who cooked and most probably had inadequate hygienic habits , infected 13 people .
starting 1990 we performed studies with the support of the international development research center , ottawa , canada in order to evaluate different intervention measures for control of human cysticercosis ; health education related to the life cycle of t. solium and the risk factors for acquiring cysticercosis , as well as mass treatment with praziquantel against taeniosis [ 7,20 - 24 ] .
a huge field study was established along 2 years in which all the inhabitants of 3 communities ( around 3,000 in each ) were asked for blood and fecal samples ; in depth sociological interviews were performed in 10% of the people in order to develop the educational intervention .
praziquantel ( kindly donated by merck mexico ) was provided in 2 communities and health education in the other 2 , in such a way that 1 community received only the cestocide drug , 1 only the education program , and 1 community both measures .
praziquantel was used at 5 mg / kg weight instead of 10 mg / kg in order to avoid neurologic exacerbation if cysticerci were lodged in the brain ; but unfortunately its cestocidal effect was also reduced to 54% instead of the 95% expected .
in contrast , health education was so effective that no pigs born after the intervention had cysticerci up to 40 month after this measure was implemented
. this formidable effect could be due to the fact that people learned that if their pigs had no access to human feces ( in latrines , garbage , or due to free roaming ) they would not acquire the disease , and thus could be sold in a better price .
marshall lightowlers , and was evaluated in mexico , and later on in peru   and cameroon .
this is , up to date , the vaccine against any parasite with the highest efficiency ; 100% of immunized pigs did not develop cysticerci after experimental infections with t. solium eggs or in spite of living in highly contaminated environments .
another intervention was assessed in a jurisdiction of " el bajio " with more than 750,000 inhabitants , in which doctors in health centers were given a small flask with some t. solium proglottids , and invited to ask the patients that attended for any reason , if they or someone at home released segments as those in the flask .
patients were also asked if a member of the household had convulsive crisis or if they had " measly pigs " at home .
to those with a positive answer , praziquantel at 10 mg / kg was offered .
announcements in walls , radios , newspapers , and short courses were provided in the entire jurisdiction .
the year before and at the end of the year in which the intervention took place , annual data were obtained from the official disease notification system at the ministry of health ; 7 cases vs 41 of taeniosis were detected before and after ; also ncc increased from 16 to 68 cases and swine cysticercosis from 2 to 17 , because people became aware of the disease .
all tapeworm carriers were treated ( 4 worms were t. solium , the remainings were t. saginata ) , as expected only 10% of the tapeworms were t. solium .
i consider that i am closing my research circle on cysticercosis , since this disease has been controlled in mexico .
this reflection is based on the dramatic decrease in the frequency of human ncc and of human taeniosis that has been taking place in mexico in the last 20 years , according to the official national notification system that is collected by the ministry of health .
the explanation for this reduction is based on a sequence of events that started with the publications produced along the last 40 years by mexican scientific and medical communities working on cysticercosis .
the vast amount of information published most probably promoted the establishment of a national program for the control of t. solium ( guidelines for the prevention and control of taeniosis and cysticercosis , nom 021 ssa2 - 1994 , 2004 ) that are obligatory to follow in the whole nation , lead by the ministry of health . finally , in mexico
, a general improvement of living conditions has taken place , which has had a positive impact in the reduction of ncc and swine cysticercosis .
the last aspect of this review is to focus towards comparing research related to t. solium and t. asiatica .
the main concept is to understand the difference between having the disease and being a tapeworm carrier .
cruz et al . , in their operational studies on the control of t. solium taeniasis / cysticercosis in ecuador , calculated that expulsion of a tapeworm by at least 148 carriers reduced the exposure to t. solium eggs both for man and pigs in the study areas , and considered that with a relatively low reinfection rate , this human reservoir of infection would remain diminished for several years . in this way
, the real disease , ncc , can be controlled . on the other hand , the group of jeon et al .   described that nationwide surveys conducted every 5 years in korea revealed that the positivity rate for taeniid eggs decreased from 1.9% in 1969 to 0.02% in 1997 , and human taeniosis was no more detected in the 2004 survey .
.   also indicated that during the period of 1998 and 2002 , a total of 19,894 chinese inhabitants of 3 ethnic minorities in guangxi province , china were surveyed for taenia worms .
a total of 927 ( 4.7% ) persons discharged proglottids , and , in 2002 , 108 were treated , and 117 adult tapeworms were recovered . using surveys in order to retrieve tapeworms in asian countries suggests that carriers do not attend health institutions for clinical symptoms , indicating that taeniosis does not cause a disease .
i personally consider that the 3 species of human tapeworms should be dealt as different concepts .
t. solium has to be eliminated from carriers because it is the main risk factor for ncc , a devastating disease ; t. saginata causes minor symptoms due to the discharge of proglottids .
the adult parasites of t. asiatica do not cause disease , since they are not associated with symptomatology that requires medical treatment .
the 2 most important justifications of my reasoning are : 1 ) in the last few years , clinical and basic studies are demonstrating with increased numbers of publications and of clinical successes that helminths participate in immunomodulating the intestinal milieu in order to reduce inflammatory bowl diseases ( usually referred to as ibd ) , such as crohn 's disease , that are becoming very prevalent in developed countries around the world [ 32 - 37 ] .
2 ) the world 's biodiversity is being threatened because of the huge human development ; there is no need to further reduce it .
 three species of tapeworms infect humans in their adult stage ( taenia solium , taenia saginata and taenia asiatica ) . 
 the 3 are flat , opaque white or yellowish , and exceptional long segmented parasites , measuring 1 to 12 m in their adult stage . in this review , 
 the development of the knowledge regarding the first species , mainly focused on understanding how the larval stage or cysticercus is transmitted to humans , is described . 
 the second species is a cosmopolitan parasite that only causes taeniosis and not cysticercosis ; therefore , it will not be included . 
 information on the third species , which is presently being produced , since this species was recognized as such only at the end of the 20th century , will be discussed at the end of this review . 
MORPHOLOGY AND LIFE CYCLE OF 
ANTI-
EVALUATION OF INTERVENTION MEASURERS FOR CONTROL
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