Surra

Surra is a tropical protozoal disease of mammals caused by the flagellate parasite Trypanosoma evansi. It affects a wide range of domestic and wild hosts, most notably horses, ponies, donkeys, camels, cattle, water buffalo, and goats. The disease is found in Africa, Asia, and the Americas, particularly in areas with abundant biting flies.

Transmission occurs primarily by mechanical inoculation through hematophagous flies such as horse flies (Tabanidae) or stable flies, rather than by a biological vector cycle. The parasite can also be transmitted through contaminated needles or blood. There is no strict species barrier, and mixed infections are possible in areas with diverse livestock.

Clinical signs vary but commonly include fever, depression, rapid weight loss, anemia, edema (especially of the limbs and face), pale mucous membranes, tachycardia, and enlarged spleen or liver. Abortions may occur in pregnant animals. In chronic cases, animals may show intermittent fever and reduced production or performance.

Diagnosis relies on a combination of methods. Direct visualization of motile trypomastigotes in blood smears can confirm active infection. Serological tests such as ELISA or indirect immunofluorescence detect antibodies but may not distinguish active from past infection. Molecular methods like PCR can detect parasite DNA and aid in confirmation, particularly in chronic cases or post-treatment monitoring.

No widely available vaccine exists. Control focuses on reducing exposure to vectors, improving fly control and housing, implementing quarantine and movement controls during outbreaks, and treating infected animals with trypanocidal drugs such as suramin or diminazene aceturate where appropriate. Drug resistance has been reported in some regions, underscoring the need for integrated management. Human infections are rare but have been reported, typically in individuals with close contact to infected animals.