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 T. brucei. T. 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 B. 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.

Transmission was successfully halted on Zanzibar by sterile insect technique (SIT) of the vector Glossina austeni.

Signs and symptoms
The incubation period ranges from four days to approximately eight 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.

Control measures
If the outbreak is detected early, the organism can be destroyed by quarantines, movement controls, and the euthanasia of infected animals. Tsetse fly populations can be reduced or eliminated by traps, insecticides, and by treating infected animals with antiparasitic drugs. The tsetse habitat can be destroyed by alteration of vegetation. Some drugs can prevent trypanosomiasis, and are called prophylactic drugs. These are very effective in protecting animals during the times they are exposed to diseases. Historically, these drugs were not used properly, leading to some resistance.

Waterbuck, among other animals, produces chemical odours that repel tsetse flies. This has led to the development of collars that store and gradually release these chemicals, reducing tsetse attack and thus trypanosomiasis incidence for cattle wearing these collars.

Economic impact
Although the loss of direct livestock products (meat, milk, and blood) is problematic, the greatest impact of livestock trypanosomiasis is the loss of crop productivity due to loss of the animals' draught power in the field.