Immunity to coccidiosis: effect of betamethasone treatment of fowls on Eimeria mivati infection

Daily 1 mg doses of a cortisone derivative, betamethasone, caused an increase in oocyst production and extended the patent period of E. mivati infections in partially immunized chickens. The more prolonged the course of cortisone injections, the greater the effect, although this was substantial when only a single dose was given, especially if this was at or near to the time of oocyst inoculation. E. mivati infections in susceptible chickens were similarly affected but not to such a great extent. The possible means whereby cortisone treatment reduces acquired immunity to E. mivati infection are discussed. Thanks are due to Mrs P. Hesketh and to other members of the parasitology department for technical assistance, also to the senior poultry attendant for care of the animals. Mr C. C. Wannop examined several of the birds post mortem.