Immunity to coccidiosis: protective effect of transferred serum in Eimeria maxima infections

Serum taken between 2 and 3 weeks after infection of the donors with E. maxima conferred a considerable degree of protection against infection with the homologous organism when injected daily into young recipients. Different pools of such sera had differing activities, but the majority gave protection of 50% or more whereas a few were inactive. The degree of protection obtained was dose-dependent, varying directly with the volume of serum injected and inversely with the size of the challenge oocyst inoculum. A course of injections started early in the life-cycle had a greater effect than those started in mid- or late cycle even when comparatively large volumes of serum were given. Protection was species specific; serum obtained from birds infected with E. maxima did not protect against E. praecox or E. acervulina. The assistance of Mrs Patricia Hesketh is gratefully acknowledged, as is the help of other members of the staff of the Parasitology Department. Mr P. Townsend, Senior Poultry Attendant, supervised the cleaning and sterilization of cages and the collection of faecal samples.