Duration of immunity to East Coast fever (Theileria parva infection of cattle)

Forty-five cattle, which had recovered from EOF and been kept free from reexposure to infection for periods of 1–43 months, were given a single uniform lethal challenge using a stabilate prepared from triturated infected ticks. All withstood the challenge which killed the five controls. There was an increase in the incidence of mild febrile reactions with time since last exposure to T. parva, indicating a gradual loss of immunity in the absence of reinfection. The duration of the immunity was not related to the severity of the initial reaction.We are indebted to our colleagues on the Immunological Research on Tickborne Cattle Diseases and Tick Control Project, with whom we designed and carried out the experiment.