Resistance toEimeriainfections in the chicken: the effects of thymectomy, bursectomy, whole body irradiation and cortisone treatment

SUMMARY Surgical bursectomy or thymectomy at day old had little effect on primary or subsequent infections withE. brunetti or E. maxima. Whole body irradiation of day-old chickens with 700 or 750 R did not affect the development of immunity to theseEimeriaspp., but in some experiments it affected oocyst production during initial infections. In one of four trials, birds surgically bursectomized and irradiated produced twice as manyE. brunettioocysts during an initial infection as the irradiated only controls; in the remaining three trials, oocyst production in the operated birds was either similar to or slightly greater than that in the controls. Combined bursectomy and irradiation did not affect immunity to re-infection. Combined thymectomy and irradiation had little effect on primary infections (increased oocyst output was found in only one of six trials) and no effect on subsequent immunity; mean body weights and circulating lymphocyte numbers were decreased but tuberculin sensitivity was reduced in only a small proportion of the birds, indicating that the cell mediated immune responses of the majority were not affected. Small (0.75 mg) daily doses of cortisone acetate given to irradiated birds or irradiated thymectomized birds, did not affect resistance to reinfection withE. brunetti. We wish to thank Dr B. M. Freeman for surgical bursectomy; Mr E. A. King, Department of Radiotherapeutics, University of Cambridge, for irradiation and members of the technical staff of the Parasitology Department for their willing and skilled assistance.