Chicken coccidiosis: correlation between resistance and delayed hypersensitivity.

Broiler chickens were immunized with viable oocysts of Eimeria necatrix, E. tenella, or with a commercially prepared vaccine (CocciVac D) containing oocysts from eight chicken Eimeria species. Before challenge with oocysts of E. necatrix or E. tenella, delayed hypersensitivity (DH) reactions to particulate-oocyst antigen extracts of E. nectrix, E. maxima, and E. tenella were demonstrated in the previously immunized broilers. Broilers immunized, tested for DH, and challenged showed good corrrelation between DH reactions and resistance in each homologous trial. Birds immunized with CocciVac D also gave good correlation between DH reactions to E. maxima, E. necatrix, or E. tenella antigens and resistance when challenged with E. necatrix or E. tenella oocysts. Oocyst antigens from E. maxima, E. necatrix, or E. tenella were cross reactive for DH, indicating some antigen sharing among species of chicken coccidia. A few broilers immunized with chicken coccidia showed DH to an oocyst antigen from E. bovis, a cattle pathogen. Results show that DH to oocyst antigens can predict resistance to coccidiosis.