Is the Oriental House Rat (Rattus tanezumi) a Potential Reservoir for Trypanosoma evansi in Thailand?

Abstract Trypanosoma evansi is a protozoan blood parasite and etiologic agent of “surra,” a disease affecting a wide range of domestic and wild mammals, some identified as potential reservoirs. Although T. evansi has been detected in several small wild rodent species, their role in the epidemiology of surra is unclear. There is molecular evidence of T. evansi in wild rodents in Asia, but it is not known whether they can carry the parasite for sufficient time to significantly contribute to the epidemiology of surra. We assessed the susceptibility of the Oriental house rat (OHR; Rattus tanezumi) to T. evansi infection. Five adult male OHRs trapped in Bangkhen district, Bangkok, Thailand, and five laboratory Wistar rats (Rattus norvegicus) as positive controls, were experimentally infected with a local strain of T. evansi. The five controls and three of the five OHRs were highly susceptible and rapidly exhibited the high levels of parasitemia usually observed in Wistar rats. They died or were euthanized just prior to expected death. Two OHRs presented fluctuating levels of parasitemia, without obvious clinical signs, throughout 40 d of monitoring. These results highlight the moderate susceptibility of some OHRs and their ability to carry the infection over time. Along with the molecular evidence of T. evansi in captured OHRs (demonstrated elsewhere), our results bring new information on the potential role of OHRs in the complex epidemiology of surra.