Research into the relative importance of Tabanidae (Diptera) in mechanical disease transmission. IV. A contribution to the epidemiology of bovine trypanosomiasis in Africa

In further studies on disease transmission by tabanids in Tanzania [see RAE/B 63, 3448; 64, 565], the incidence of trypanosomiasis (caused by Trypanosoma spp.) was studied in a herd of dairy cattle near Dar es Salaam over a period of 4 months. The apparent density of Glossina and prevalence of various species of tabanids were measured.There was no statistical correlation between the disease incidence and the seasonal occurrence of tabanids. Although anaplasmosis [caused by Anaplasma marginale] was concurrently transmitted by Tabanus taeniola P. de B. on an economically significant scale in this herd and there was a high incidence of infections with Trypanosome vivax, it was thought that trypanosomes were transmitted by tabanids at an insignificant rate. The only measurable result of such mechanical transmission was a change of the T. vivax: T. congolense ratio in favour of T. vivax (69% of the infections) over a period of 4 years from a ratio of 37%, at a time when a Glossina control campaign was in operation.