The use of tissue culture attenuated live vaccine for Theileria hirci.

Malignant sheep theileriosis which is a tick-borne disease is caused by the protozoan parasite Theileria hirci. The pathogenic form of the parasite, schizonts, inhabits the lymphoid cells of the mammalian host, and if an immunity is engendered against them animals can resist the infection. Theileria hirci infected lymphoid cells were cultivated in vitro, using Eagle's MEM supplemented with 10% ovine serum, yeast extract and lactalbumine hydrolysate (YL), respectively 250 and 1250 mg/L. Schizonts of the parasite which propagated synchroneously with the lymphoid host cells, and had been attenuated in the course of time, were used as an immunizing live vaccine at a passage level (100) that did not produce the erythrocytic forms of the parasite and was harmless to the recipient animals. The vaccinal dose contained 5 X 10(5) infected cells. The vaccine was preserved at -70 degrees C and dispatched to the field under the 4 degrees C condition with a shelf-life of 5 days. Experimental and mass field vaccination have been carried out. The first and second challenge tests, performed on experimentally vaccinated animals, were carried out respectively two and six months post-vaccination. Ticks infected with a heterologous strain of T. hirci were used in the challenge tests. All controls died of acute theileriosis whereas the vaccinated animals resisted the challenge tests. Further mass vaccination is planned.