evansi

Trypanosoma evansi is a parasitic protozoan in the family Trypanosomatidae, known for causing surra in a wide range of domestic and wild mammals. It is a member of the subgenus Trypanozoon and is especially associated with horses, donkeys, camels, cattle, buffalo, dogs, and various wildlife. Many isolates of T. evansi are kinetoplast DNA-deficient (akinetoplastic), a feature that prevents development in tsetse flies and makes transmission predominantly mechanical through hematophagous flies such as tabanids (horseflies) and Stomoxys (stable flies). The parasite circulates in the bloodstream and body fluids and can invade tissues, leading to a chronic, debilitating disease.

Clinical signs of surra include fever, progressive anemia, edema, weight loss, weakness, and sometimes ocular lesions. Reproductive losses such as abortion may occur. Acute infections can be fatal if untreated, while chronic infections may be more insidious and difficult to diagnose.

Diagnosis relies on multiple approaches. Direct demonstration of circulating trypomastigotes in blood or body fluids by microscopy or parasite concentration techniques is common. Serological tests, including agglutination-based assays and ELISA, and molecular methods such as PCR, support diagnosis and species confirmation.

Treatment and control hinge on antiprotozoal drugs like suramin and diminazene aceturate, which are more effective in early infections; resistance and reduced efficacy in chronic cases are concerns. There is no widely available vaccine. Preventive measures focus on vector control, regular screening of at-risk livestock, and movement restrictions to prevent spread.

Geographically, T. evansi is found in tropical and subtropical regions of Africa, Asia, the Middle East, and parts of the Americas, where it imposes significant economic impacts on pastoral and transport-related livestock systems.