Further Studies on the Immunization of Cattle against Theileria La Wrencei by Infection and Chemoprophylaxis

Abstract

Three experiments were carried out to ascertain the feasibility of immunization of cattle against Theileria lawrencei using infection and chemoprophylaxis. In the first two experiments, cattle were immunized with a combination of three theilerial strains (‘cocktail’) and simultaneous treatment with an experimental formulation of oxytetracycline. When groups of these immunized cattle were challenged with stabilates of T. lawrencei isolated from African buffalo captured in Kenya and Tanzania, many of the immunized cattle had severe reactions and 3 out of 20 died, as did 18 of the 20 controls. A paddock containing carrier buffalo which maintained a population of Rhipicephalus appendiculatus continuously infected with T. lawrencei, was used in a second and third experiments. Cocktail immunized and control cattle were exposed to this tick challenge, and 55% of the immunized animals and 91% of the controls died. The protection provided by cocktail immunization was compared with immunization using different isolates of T. lawrencei from the buffalo paddock, but little difference in the degree of protection was detected. However, a high degree of immunity was observed when cocktail immunized cattle which had undergone a T. lawrencei stabilate challenge were exposed in the paddock. Only mild reactions were seen and no deaths occurred. Field immunization of cattle against T. lawrencei may be difficult due to immunovariants of this parasite emanating from the buffalo populations.