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. Transmission Most trypanosomes develop in tsetse flies (Glossina spp.), its biological vector, in 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, and syringes. The most important vectors are thought to be horseflies (Tabanidae spp.) and stable flies (Stomoxys spp.). The immune response of animals may be unable to eliminate trypanosomes completely, and the host may become an inapparent carrier. These inapparent infections can be reactivated if the animal is stressed. Transplacental transmission can also occur. Signs and symptoms The incubation period ranges from 4 days to approximately 8 weeks. The infection leads to significant weight loss and anemia. 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. Vectors Diagnosis The diagnosis of African animal trypanosomiasis encompasses mainly the identification of the trypanosoma parasite when viewed under a microscope using a sample of blood (primarily) or lymph fluid (especially T.vivax) from an infected animal. Other techniques for detecting the parasite apart from direct microscopy include concentration techniques and animal inoculation. To identify trypanosomes or treat trypanosomiasis, a variety of diagnostic techniques are available. The sensitivity and specificity of current diagnostic tests, as well as how simple and expensive they are to use, vary. The selection of one or more specific tests is influenced by epidemiologically appropriate diagnostic needs, equipment and skill availability, and economic criteria. The majority of parasitological methods, with the exception of the thick