from may through october 2008 , we trapped small mammals at 5 sites in southern sweden ( figure 1 ) .
our primary objective was to obtain samples from bank voles , myodes glareolus , but other species were also sampled when captured .
a nested pcr was performed with primers for anaplasmataceae specific for the 16s rrna gene ( 10 ) .
prevalence of infection : hglinge , n = 45 infections , 0% candidatus n. mikurensis , 44.4% bartonella spp . ; revinge , n = 623 infections , 9.3% candidatus n. mikurensis , 33.7% bartonella spp . ; istaby , n = 53 infections , 3.8% candidatus n. mikurensis , 34% bartonella spp . ; hemmestr , n = 64 infections , 4.7% candidatus n. mikurensis , 39.1% bartonella spp . ; herseby , n = 49 infections , 12.5% candidatus n. mikurensis , 45.0% bartonella spp .
all amplified fragments were sequenced , and a blast ( http://blast.ncbi.nlm.nih.gov/blast.cgi ) search showed that 68 animals were infected by candidatus n. mikurensis .
the primers were chosen to be specific for bacteria belonging to the families rickettsiaceae and anaplasmataceae ( 10 ) , but they also amplified bartonella spp . under the given pcr conditions . in total ,
, as indicated by double peaks on the sequencing chromatogram , occurred in 12 cases . to further characterize the obtained candidatus n. mikurensis
, we sequenced 1,426 bp of the 16s rrna and 1,233 bp of the groel gene ( 1 ) .
the obtained 16s rrna candidatus n. mikurensis sequences in this study were identical ( 1,426/1,426 bp ) to sequences obtained from human patients in germany and switzerland ( 2,3 ) .
the groel sequence was identical to the isolate from germany ( 1,233/1,233 bp ) but differed slightly from the isolate from switzerland ( 1,072/1,084 bp , 98.9% pairwise identity ) .
a phylogenetic network containing unique 16s rrna sequences from candidatus n. mikurensis available at the national center for biotechnology information was made with the program network 4.5.1.6 ( www.fluxus-engineering.com ) by using the median - joining algorithm ( 11 ) ( figure 2 ) .
phylogenetic network of 16s rrna sequences ( 1,231 bp ) from candidatus neoehrlichia mikurensis , southern sweden , 2008 .
numbers on branches represents mutations , numbered according to nucleotide position in the alignment . the sequence obtained in this study
is shown in boldface and is identical with sequences from human patients in germany ( 3 ) and switzerland ( 2 ) .
the japanese reference strain tk4456 ( 7 ) showed 99.2% similarity with our sequence , and the north american candidatus n. lotori strain ( 12 ) showed 98.3% similarity .
the prevalence of candidatus n. mikurensis at the 5 sites ranged from 0% to 12.5% , and bartonella spp . occurred in 33.7% to 45.0% of the animals ( figure 1 ) .
candidatus n. mikurensis occurred in all 4 rodent species , but not in the shrews ; the difference in prevalence between rodents and shrews was statistically significant ( p = 0.011 , by fisher exact test ) .
in the present field survey of anaplasmataceae in swedish rodents , we have amplified 16s rrna and groel sequences identified as candidatus n. mikurensis identical to sequences obtained from humans .
this organism has been amplified from humans with febrile illness on 4 occasions ( 13 ) , demonstrating that candidatus n. mikurensis can cause human infections , at least occasionally .
apart from the first human case , to our knowledge , candidatus n. mikurensis has not been detected in sweden .
however , we identified candidatus n. mikurensis at 4 of 5 sites , indicating that this organism is widespread in southern sweden .
identical or similar sequences have been detected in ixodes ricinus ticks from several european countries ( 36,13 ) , showing that it is distributed over a large area of europe .
i. ricinus is the dominating tick species in sweden , and animals at all our study sites were heavily infested with larvae of this species and occasionally with nymphs ( m. andersson and l. rberg , unpub .
reservoir hosts are essential for several tick - borne pathogens that lack the capacity for transovarial transmission from female ticks to larvae , such as a. phagocytophilum ( 14 ) .
approximately 70% of the tick larvae in sweden engorge on small mammals , such as voles , mice , and shrews ( 15 ) .
the prevalence of candidatus n. mikurensis was similar in all investigated rodent species in our study with a mean value of 8.8% .
these results are consistent with several studies in japan , which also found candidatus n. mikurensis in several different rodent species ( 7,10 ) .
this finding indicates that rodents play a role in the natural cycle of candidatus n. mikurensis in europe and that rodents are likely to be competent reservoir hosts .
in contrast , the closely related candidatus n. lotori , found in the united states , seems to use raccoons rather than rodents as hosts ( 12 ) . whether the european variant of candidatus neoehrlichia is capable of infecting animals other than rodents and humans remains to be investigated .
we found the organism was completely absent in shrews , which suggests that they might not be competent hosts for these bacteria . we conclude that candidatus n. mikurensis is geographically widespread in southern sweden and that several rodent species , the main source of blood meals for larvae of i. ricinus in sweden ( 15 ) , can be infected .
the relatively high prevalence in common rodent species suggests that the risk for humans and domestic animals to encounter infected i. ricinus nymphs and adults is substantial .
thus , candidatus n. mikurensis should be considered when diagnosing bacterial infections associated with tick bites .
 we examined small mammals as hosts for anaplasmataceae in southern sweden . of 771 rodents , 68 ( 8.8% ) 
 were infected by candidatus neoehrlichia mikurensis , but no other anaplasmataceae were found . 
 candidatus n. mikurensis has recently been found in human patients in germany , switzerland , and sweden , which suggests that this could be an emerging pathogen in europe . 