Animal African trypanosomiasis, also known as nagana and nagana pest, is a disease of vertebrate animals. The disease is caused by trypanosomes of several species in the genus Trypanosoma such as Trypanosoma brucei. Trypanosoma vivax causes nagana mainly in West Africa, although it has spread to South America. The trypanosomes infect the blood of the vertebrate host, causing fever, weakness, and lethargy, which lead to weight loss and anemia; in some animals the disease is fatal unless treated. The trypanosomes are transmitted by tsetse flies.
An interesting feature is the remarkable tolerance to nagana pathology shown by some breeds of cattle, notably the N'Dama – a West African Bos taurus breed. This contrasts with the susceptibility shown by East African Bos indicus cattle such as the zebu.
This disease is the nonhuman animal counterpart of human African trypanosomiasis, also known as sleeping sickness.