Trypanosoma evansi



Surra is a disease that occurs mainly in horses and camels. It is caused by infection with Trypanosoma (T.) evansi, a unicellular parasite. It is not dangerous for humans.


Africa, Asia, Central and South America

Host animals

Horses, donkeys, mules, camels, llamas, buffaloes, cattle, sheep, goats, dogs, cats

Infection route

Transmission by blood-sucking flies and vampire bats. Carnivorous animals can become infected by feeding on infected meat

Incubation time

5-60 days


Fever or episodes of fever, anemia, severe weight loss, jaundice, progressive weakness and lethargy, bruising, paralysis.


Therapy is currently not possible


There is no vaccination

Situation in Austria

The pathogen of Surra, the parasite Trypanosoma evansi, does not occur in Austria.

Technical information

Surra is caused by infection with Trypanosoma (T.) evansi, a single-celled parasite.

Many domestic animals and some wild species are susceptible: horses, mules, donkeys, cattle, buffaloes, camels, llamas, pigs, sheep, goats, dogs, cats, deer and capybaras. Depending on the geographical region, the main hosts vary: most affected in South America are horses; in China, horses, mules, buffaloes and deer; in Southeast Asia, horses, cattle, buffaloes; and in the Middle East and Africa, camels.

Transmission is by bloodsucking flies including Tabanus spp. (horseflies) and Musca spp. (true flies), with the parasite most commonly transmitted by horseflies. Trypanosomes survive only a short time outside their host. Flies can no longer transmit the pathogen after about 8 hours. Vampire bats (in South and Central America) are hosts, reservoirs, and vectors. They transmit T. evansi with their saliva and can develop high parasitemia. This can also lead to death of the bats. Surviving bats can further transmit the pathogen (carriers). Carnivores can become infected via infected meat.


The incubation period varies between 5-60 days, there is high fever, progressive anaemia, weight loss, jaundice, weakness and lethargy, oedema (especially in the lower part of the body). In horses, it can also cause damage to the nervous system, ataxia, paralysis, especially of the hindquarters, and even death. Trypanosoma evansi can also cause abortion in buffaloes and camels. The disease is often fatal in camels and horses. Death can occur after 2-4 weeks, in the case of chronic infection up to 2 years can pass.


Detection method:

  • Blood smear
  • molecular biological methods (PCR)
  • detection of antibodies by ELISA
  • detection of antibodies by CATT (card agglutination test) / T.evansi


Institut für veterinärmedizinische Untersuchungen Mödling

Last updated: 10.10.2023

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