Cattle theileriosis in China.

Amongst the piroplasmoses of livestock in China, the commonest theilerioses are caused by Theileria annulata, T. sergenti and T. mutans. Research carried out over many years has shown these to be distributed mainly in Northern China but they also occur in Southern China. T. annulata and T. sergenti are the most troublesome, affecting large numbers of cattle, especially those of exotic breeds. The incident rate and numbers of fatalities vary widely between areas and breeds of cattle. T. annulata is the most virulent species having an incident rate of 11-46% for indigeneous cattle and causing death rates of between 11-40.8%. For exotic cattle in areas free of T. annulata the sickness rate is up to 61% and mortality rates up to 31%. T. sergenti is avirulent in cattle and clinical symptoms are rarely observed, however, in some areas the infection rate could possibly be as high as 97.5%. Dairy and hybrid cattle imported from other places proved highly susceptible, with mortality rates possibly reaching 14%. The pathogenic forms, clinical signs, tick vectors and the effects of chemical and immune intervention are also discussed in this paper.