Correlation between immune responses and oocyst production in chickens monospecifically infected with Eimeria maxima

One-day-old chicks (Cobb 500) were purchased from a commercial hatchery and raised on non-medicated diet in wire cages in coccidia-free conditions. The chickens were infected with a single dose (1 x 10(4)) of sporulated oocysts of E. maxima by direct injection into the crop at 5 weeks of age. Antibody capture immunoassay (ELISA) and lymphocyte proliferation assay were used for assessment of antibody and cellular responses, respectively. The results showed that both antibody and lymphocyte responses increased during the experiment and reached their highest level at 2 weeks post-inoculation, when they began to decline. A significant negative correlation between lymphocyte proliferation and oocyst output was observed. This study demonstrates that the whole-blood lymphocyte assay is a useful, relatively simple, sensitive and reliable technique for quantitative assessment of circulating T-cell responses. Assessment of lymphocyte proliferation and antibody responses may have applications in monitoring flock status in outbreaks of avian coccidiosis and evaluation of the efficacy of vaccination programmes in poultry.