Studies on occurrence, transmission and potential mechanical vectors of camel trypanosomiasis in northern Kenya

Abstract

Trypanosoma evansi ,Steele 1885 infection in northern Kenya camels was diagnosed by an enzyme-linked immunosorbent assay (ELISA), mouse inoculations. and blood smears. The ELISA results indicated a current or past trypanosome prevalence rate that ranged from 73% to 95% in the sampled camel herds. The blood smear test revealed a maximum of 11.5% and a mean of 3.9% infection rates while the mouse inoculations revealed a maximim of 19.2% and a mean of - 11.3% infection rate in the sampled herds. The mouse inoculation test (MIT) was found to be the most sensitive and suitable means of diagnosis of camel trypanosomiasis in northern Kenyan camels. Trypanosome infection rates were elevated during the wet season months as diagnosed by MIT. The mean trypanosome infection rate was 13.7 + /-5% for the wet season and 4.55+ I =2% for the dry season. Absence of Glossina spp. in northen Kenya suggests mechanical transmission of trypanosomiasis in this region. Mechanical transmission is the mode of transmission whereby a parasite is transferred from one host to another without undergoing development within a vector. Mechanical transmission of camel trypanosomiasis within northern Kenya was ascertained by regular monitoring of 10 sentinel camels. Three of these animals became infected 7-9 months after introduction, in the absence of Glossina spp. Glossina spp. were not identified in the study area following monitoring by biconical traps. Biting flies identified in the study area using sweep-nets and biconcal traps comprised of six tabanids, two hippoboscids and two muscids. Results of this study showed a seasonal abundance of these flies during and after the rains, which coincided with outbreaks of camel trypanosomiasis. This coupled with the fact that the major camel trypanosome T.evansi , is transmitted only mechanically, and infection of sentinel camels in the absence of Glossina spp., suppport and confirm the occurrence of mechanical transmission in nature. Laboratory experiments showed that a tabanid (Haematopota brunnescus, Ricardo), Stomoxys calcitrans Linnaeus, and Glossina morsitans morsitans Westwood, could mechanially transmit T. evansi from infected to non-infected mice . Dissection and inoculation of fly mouthparts into mice revealed that these fly mouthparts could contain viable trypanosomes for several minutes after infective blood meals. Dissection of mouthparts of field collected H.camelina, H.minuta. and, T taeniola after infective blood meals on camels revealed mean trypanosome infection rates of 14.5%, 23.3% and 27.4% respectively. Inoculation of triturated mouthparts of H.camelina, H.minuta and Ttaeniola (following blood meals on infected camels) infected 6%, 12% and 53.3% of mice inoculated respecively. These dissection and inoculation experiments further support the concept of mechanical transmission of trypanosomes by haematophagous insects.