Home Livestock & Diseases Livestock diseases Animal African Trypanosomosis
Also known as nagana or nagana pest, Animal African Trypanosomosis (AAT), is a protozoan parasitic disease of vertebrate animals. It affects cattle, water buffalo, sheep, goats, horses, pigs, dogs and other species.

Causative agent

The disease is caused by the protozoan parasites Trypanosoma congolense, Trypanosoma vivax and, to a lesser extent, Trypanosoma brucei brucei which are all mainly transmitted by tsetse flies.


From the southern edge of the Sahara desert to Zimbabwe, Angola and Mozambique in the South.


Animal African Trypanosomosis (AAT) is estimated to kill 3 million cattle annually. Losses directly attributed to trypanosomosis from reduced meat and milk production, and the cost of treatment and vector control, are estimated to be USD $1.2 billion. Losses in agricultural gross domestic product for all tsetse-infested lands was estimated to be USD4.75 billion per annum.


Most trypanosomes develop for one to a few weeks in tsetse flies (Glossina spp.), which act as biological vectors. The parasites are transmitted to the host animal in saliva when a fly bites the host. Trypanosomes can also be spread by fomites such as surgical instruments and mechanical vectors  like biting flies including horse flies—especially T. vivax.

Clinical signs

The incubation period for AAT is four days to approximately eight weeks. Although acute cases may be seen, trypanosomosis is often a chronic disease in susceptible animals. Trypanosomes infect the blood of the host causing fever, weakness, lethargy and anaemia, which lead to weight loss and a reduction in fertility and milk production.


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 flies. Infected animals can be treated with drugs, but drug resistance has been observed. The selection of trypanosome tolerant breeds of cattle can lessen the impact of infection. No vaccine is available to prevent trypanosomiasis.

For further information, view our AAT product development work.