Animal trypanosomiasis
Parasitic disease of vertebrates
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Through Milk
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 non-Glossina 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.
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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.
Vectors
Control measures
Trypanocidal antiparasitic drugs are the main tool used in Africa to control animal trypanosomiasis. Some drugs can prevent the disease, and are called prophylactic drugs. These can be very effective in protecting animals during the times they are highly exposed to diseases. However, historically these drugs were not always used properly, leading to some resistance. Recently, efforts are being made to bring new trypanocides to the African market, although challenges to entry persist. Tsetse fly populations can be reduced or eliminated by traps and insecticides. The tsetse habitat can be destroyed by alteration of vegetation, although this approach is no longer deliberately adopted for environmental reasons. In most settings, an integrated, community-based approach to animal trypanosomiasis control is recommended, whereby the control of vectors is combined with the rational use of drugs under the overall guidance and supervision of the national veterinary services.
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.
Epidemiology
As with other infectious diseases, climate change will have an effect on the distribution and the risk of transmission of animal trypanosomiasis. However, it depends on the geographical region, disease-carrying species, the exact climate change scenario, and many other factors whether there will be a decrease or increase in animal trypanosomiasis.