Control of tropical theileriosis with attenuated schizont vaccine in China.

Tropical theileriosis, a tick borne disease of cattle caused by the protozoan Theileria annulata, was widely distributed in northern China causing great economical losses before the 1980's. In the 1960's blood passaging, irradiation and in vitro culture of parasite were used for the development of attenuated vaccine. Two lines of the schizont stage were obtained which both provided sufficient protection against tick infestation or blood challenge in experimental and field trials. A gelatin protection technique allowed storage at 4 degrees C, significantly prolonged shelf life and permitted transport without a cold chain. The vaccines were commercialized and widely administered in epidemic areas, leading to control of T. annulata infection in China.