The disease is caused by protozoan trypanosomes from the genus Trypanosoma. ATT is caused predominantly by species T.congolense and T.vivax, and to a lesser extent by T.brucei brucei. The trypanosomes are mainly transmitted by tsetse flies.
From the southern edge of the Sahara desert to Zimbabwe, Angola and Mozambique in the South.
Trypanosomoses affecting cattle are the most important economically since they are a major cause for reduced meat and milk production and draught power for agricultural production. In cattle, the mortality rate can reach 50-100% within months after exposure, particularly when poor nutrition or other factors contribute to debilitation. The total yearly cost of the disease is estimated to be US $628 million.
Most trypanosomes develop for one to a few weeks in tsetse flies (Glossina spp.), which act as biological vectors. The parasites are transmitted by saliva when the fly bites the animal. Trypanosomes can also be spread by fomites and mechanical vectors including surgical instruments and various biting flies including horse flies (especially T. vivax).
The incubation period is four days to approximately eight weeks. Although acute cases can be seen, trypanosomosis is often a chronic disease in susceptible animals. The trypanosomes infect the blood of the host causing fever, weakness, lethargy and anaemia, which lead to weight loss as well as fertility and milk reduction.
AAT can be controlled by reducing tsetse fly populations with traps and insecticides. Animals can be given antiparasitic drugs prophylactically in areas with a high population of trypanosome-infected tsetse. Infected animals can be treated with drugs, but drug resistance has been observed. The selection of trypanosomosis tolerant breeds of cattle can lessen the impact of trypanosomosis. No vaccine is yet available for this parasitic disease.
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