Animal trypanosomiasis

Animal trypanosomiasis, also known as nagana and nagana pest, or sleeping sickness, is a disease of vertebrates. 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.

Most trypanosomes develop in tsetse flies (Glossina spp.), in its biological vector, about one to a few weeks. When an infected tsetse fly bites an animal, the parasites are transmitted through its saliva. It can also be spread by fomites such as surgical instruments, needles, syringes. The most important vectors are thought to be horseflies (Tabanidae) and stable flies (Stomoxys spp.).

The immune response of animals could be unable to eliminate trypanosomes completely, and the animals could become inapparent carriers. These inapparent infections can be reactivated if the animal is stressed. Also, the transplacental transmission can also occur.

The incubation period ranges from 4 days to approximately 8 weeks. The infection leads to significant weight loss and anaemia. Various symptoms are observed, including fever, oedema, adenitis, dermatitis and nervous disorders. The disease cannot be diagnosed with certainty except physically detecting parasites by blood microscopic examination or various serological reactions.

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