Tropical Theileriosis represents a serious threat to cattle health in tropical and sub-tropical regions of the world, with some 240 million animals at risk. The condition is caused by the tick-borne protozoan parasite Theileria annulata, which infects bovine leukocytes and stimulates them to proliferate in a cancer-like manner.
Infection in calves is often fatal and in older cattle meat and milk production is reduced. Critically, highly productive European breeds of cattle are particularly susceptible to the disease and this currently prevents genetic improvement of livestock in endemic regions.