Trypanosomosis (surra)

Cause and spread

Cause

The protozoan Trypanosoma evansi.

How it spreads

Mechanically, by biting flies such as horseflies and Stomoxys that carry blood from one animal to the next. No special insect is needed, so it spreads wherever biting flies feed on many animals.

Signs to watch for

• Intermittent fever and weight loss
• Anaemia and weakness
• Swollen lymph nodes
• Swelling under the belly, and of the face or throat in dogs
• Lower milk yield
• Nervous signs in some animals; horses can die quickly

Many diseases look alike. Only a laboratory test can tell them apart, so please see a veterinarian for any sick animal.

How it is diagnosed

Parasites can be seen in stained blood smears and, moving, in a drop of fresh blood. Blood is best collected while the animal has a fever. PCR detects the parasite's genes and is useful when few parasites are present.

• Usually the first testBlood Smear ExaminationLooks for the parasite in a stained blood film.Dog, Cow, Buffalo, Horse · Smear / EDTA blood
• Usually the first testWet Film Examination (Blood)Fresh blood under the microscope shows moving parasites.Dog · EDTA blood
• Confirms the diseaseTrypanosoma PCRDetects the parasite's genes.Cow · EDTA blood
• Supports the diagnosisComplete Blood Count (CBC)Shows anaemia.Dog, Cow, Buffalo, Horse · EDTA blood

Prevention and control

• Control biting flies and keep animals away from heavily infested places
• Test and quarantine new animals
• Do not reuse needles between animals
• Report suspected cases to your veterinarian or the animal husbandry department

Where this information comes from

1. Surra (Trypanosoma evansi) (factsheet) · Center for Food Security and Public Health, Iowa State University

General information for animal owners and veterinarians, last checked October 2026. It does not replace the advice of your veterinarian, who should decide which tests and treatment your animal needs.