Résumé
Trypanosoma lewisi is the type species for Herpetosoma, a homogenous subgenus of several dozen named species often described as morphologically indistinguishable, ‘‘T. lewisi-like'' parasites. These parasites normally infect rodents and utilize fleas as vectors. Although this trypanosome subgenus is considered non-pathogenic to normal hosts, some of them are on rare occasion reported in association with human disease. Recently, a T. lewisi-like infection was detected in a sick Thai infant, thus the objective of this study was to investigate the prevalence of T. lewisi infections among different rodents indigenous to Thailand. Blood was collected from a total of 129 rodents trapped from urban and rural areas of three Thai provinces (Loei, Kalasin and Phrae) between 2005 and 2006. These samples were processed for DNA isolation and tested with a PCR assay universal for the genus Trypanosoma, followed by internal transcribed spacer 1 (ITS1) sequence analysis to identify infections in positive samples. Amplicons of approximately 623 bp, the size consistent with the stercorarian trypanosome group, were generated from 21.7% of all rodents tested. Further analysis suggested that ITS1 sequences from these amplicons were 98% identical to that reported for T. lewisi from an experimentally infected rat. Only two of six rodent genera tested PCR-positive for these parasites. The highest prevalence of Herpetosoma infections was found among rodents from Phrae province (26%). These results suggest that, in Thailand, humans exposed to certain rodents or their ectoparasites could be at risk of infection with T. lewisi-like parasites. More work is warranted to identify vectors of these trypanosomes and to compare the prevalence of these infections among rodent and human populations in Thailand.