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.[1] 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.[2]

Cachectic dog infested with Trypanosoma congolense after travel in West Africa

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.[3]

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.[4]

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.[4][5]

Vectors


Disease	Species affected	Trypanosoma agents	Distribution	Glossina vectors
Nagana — acute form	antelope cattle camels horses	T. brucei brucei	Africa	G. morsitans G. swynnertoni G. pallidipes G. palpalis G. tachinoides G. fuscipes
Nagana — chronic form	cattle camels horses	T. congolense	Africa	G. palpalis G. morsitans G. austeni G. swynnertoni G. pallidipes G. longipalpis G. tachinoides G. brevipalpis
Nagana — acute form	domestic pigs cattle camels horses	T. simiae	Africa	G. palpalis G. fuscipes G. morsitans G. tachinoides G. longipalpis G. fusca G. tabaniformis G. brevipalpis G. vanhoofi G. austeni
Nagana — acute form	cattle camels horses	T. vivax	Africa	G. morsitans G. palpalis G. tachinoides G. swynnertoni G. pallidipes G. austeni G. vanhoofi G. longipalpis

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.

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References

Batista JS, Rodrigues CM, García HA, Bezerra FS, Olinda RG, Teixeira MM, Soto-Blanco B (2011). "Association of Trypanosoma vivax in extracellular sites with central nervous system lesions and changes in cerebrospinal fluid in experimentally infected goats". Veterinary Research. 42 (63): 1–7. doi:10.1186/1297-9716-42-63. PMC 3105954. PMID 21569364.
"Human African trypanosomiasis (sleeping sickness)". WHO.
Courtin D, Berthier D, Thevenon S, Dayo GK, Garcia A, Bucheton B (May 2008). "Host genetics in African trypanosomiasis". Infect. Genet. Evol. 8 (3): 229–38. doi:10.1016/j.meegid.2008.02.007. PMID 18394971.
"African Animal Trypanosomiasis" (PDF). The Center for Food Security and Public Health. Iowa State University. Retrieved 19 April 2017.
Finelle, P. "African animal trypanosomiasis". Food and Agriculture Organization of the United Nations. Food and Agriculture Organization of the United Nations. Retrieved 19 April 2017.