East Coast Fever of Cattle: 60Co Irradiation of Infective Particles of Theileria parva

Abstract

SYNOPSIS. Infective particles (IPs) of Theileria parva, the causative organism of East Coast Fever of cattle, were harvested from the tick vector, Rhipicephalus appendiculatus, using an in vitro feeding technic. In a ranging experiment, pairs of cattle were inoculated with aliquots of suspensions of IPs irradiated at doses of 4–137.6 krad. Doses of irradiation in excess of 8 krad appeared to destroy the parasite. In the 2nd and 3rd experiments, groups of 5 cattle were inoculated with aliquots of suspensions containing low and high concentrations of IPs respectively, irradiated at doses of 4–32 krad. In the 2nd experiment, doses of irradiation in excess of 10 krad appeared to destroy the parasite. In the 3rd experiment, at least 1 animal became infected when inoculated with an aliquot of a suspension irradiated at 16 krad. In all experiments, it appeared that increasing doses of irradiation destroyed increasing numbers of IPs. There was no conclusive evidence that IPs which survived irradiation were attenuated, and it appears that vaccination of cattle against ECF is unlikely to be achieved by inoculation of irradiated IPs using the methods described.