Vectors and transmission routes of animal Trypanosomiasis on the Jos Plateau north central Nigeria
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Tsetse flies, Glossina species, are the biological vectors of Trypanosoma species which cause animal African trypanosomiases (AAT) in livestock (especially cattle) in sub-Saharan Africa. This disease is often fatal without treatment and negatively impacts on rural, agricultural and economic development. On the Jos Plateau, north central Nigeria, AAT was historically of little significance due to the presumed absence of tsetse and Fulani pastoralists were encouraged to settle there. But over the last 30 years, the disease has become widespread and highly prevalent in the area. This has been attributed to the expansion of tsetse on the plateau, frequent migrations of cattle to areas with higher tsetse densities and the presence of other biting flies which serve as mechanical vectors. In the current study, the presence and abundance of tsetse was determined in selected villages using biconical tsetse trap surveys. The low number of flies trapped suggests that tsetse expansion has been very limited within the plateau but the fact that trypanosome DNA was present in over half of these flies implicates them in AAT transmission. The migration of a herd of cattle was also tracked and during the period, blood samples were collected from the cattle and examined for trypanosomes using molecular techniques. Despite prophylactic treatment and deltamethrin sprays, results showed that a significant proportion of the animals (52%) had become infected with T. vivax over the migration period. Tsetse flies (G. palpalis) were also slightly more abundant in some of parts of the migration area. Potential mechanical vectors (Stomoxys spp. and Tabanidae) were trapped and results obtained from the examination of their mouthparts for trypanosomes indicate their involvement in transmission. However, it is difficult to make any definite conclusions about their overall contribution which is thought to be minimal and more studies are needed to clarify their significance. It is concluded that trypanosomiasis risk from tsetse on the Jos Plateau is currently low and seasonal migration appears to be the main driver of AAT transmission by exposing cattle to more tsetse for longer periods. Other biting flies may play a limited role which remains undetermined. Continued monitoring of cattle and tsetse across the plateau over the next few years is important and the careful use of trypanocides and insecticide treated cattle is recommended as an appropriate control strategy.