Isolation and propagation of an Egyptian Theileria annulata infected cell line and evaluation of its use as a vaccine to protect cattle against field challenge

Abstract Tropical theileriosis is an important protozoan tick-borne disease of cattle. Vaccination using attenuated schizont cell lines is one of the methods used for controlling the disease. This study describes the production of an attenuated T. annulata cell line from Egypt and an evaluation of its use as a vaccine to protect calves against clinical disease upon field challenge. Two groups of exotic and crossbred male calves were divided into vaccinated and control groups. Vaccinated groups were inoculated with 4 ml (1 x 106 cells/ml) of the attenuated cell line. Three weeks after vaccination, calves of both groups were transported to the New Valley governorate where they were kept under field conditions and exposed to natural T. annulata challenge. All animals of the control group showed severe clinical signs and died despite treatment with buparvaquone after a severe drop in the packed cell volume (PCV). Animals of the vaccinated group became seropositive without developing serious clinical signs except for the transient fever. Post-mortem examinations revealed enlarged and fragile lymph nodes, spleen, and liver with necrosis and hemorrhages. These findings indicate that the Egyptian attenuated cell line was successful in protecting both exotic and crossbred animals against tropical theileriosis under field conditions.