theileriosis

Theileriosis is a tick-borne disease caused by protozoan parasites of the genus Theileria, primarily affecting cattle and other ruminants. It occurs in tropical and subtropical regions and can cause substantial losses due to mortality, decreased milk and meat production, and trade restrictions.

The major cattle-infecting species are Theileria parva, T. annulata, and T. orientalis. The parasites are transmitted by ixodid ticks. After sporozoites are inoculated into a vertebrate host, they invade leukocytes and develop into schizonts, driving uncontrolled lymphocyte proliferation. Merozoites released from schizonts invade red blood cells as piroplasms; ticks ingest piroplasms and carry the cycle to transmission.

Clinical signs include fever, enlarged lymph nodes, edema, poor appetite, weight loss, and anemia. Severe disease can be fatal, especially in immunologically naive animals.

Diagnosis relies on identifying schizonts in leukocytes or piroplasms in erythrocytes, supported by PCR or serology. Distribution mirrors vector presence and Theileria species; T. parva is common in eastern and southern Africa; T. annulata in parts of Asia and Africa; T. orientalis in Asia and Australia.

Control emphasizes tick control and biosecurity. Treatment uses antiprotozoals such as buparvaquone or imidocarb in some settings; vaccination exists for T. parva in defined programs but is not universally available. Management practices and surveillance help prevent introductions into naive herds.