Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2000
Publication Date: N/A
Interpretive Summary: Coccidiosis is an intestinal infection caused by intracellular protozoan parasites which belong to several different species of Eimeria. Coccidiosis seriously impairs the growth and feed utilization of livestock and poultry. Drugs are currently used to control coccidiosis. However, due to the increasing incidence of drug-resistant strains of field coccidia, a novel control strategy is needed. Since the life cycle of the organism and the host immune responses to the coccidia parasites are complex, the coccidia vaccine development has been difficult. Thus, a better understanding of how the host immune system interacts with the parasites will enhance our chances for the development of a new control strategy. In this presentation, an ARS scientist summarizes a new development in chicken immunology which is pertinent to the intestinal response to coccidia. This information will help the industry and the poultry scientists to develop a new control strategy against coccidiosis. 1
Kinetic differences between systemic vs. intestinal and humoral vs. cellular immune responses were elucidated in chickens experimentally infected with Eimeria maxima by comparing IFN-gamma and parasite-specific antibody levels in the intestine and serum during the course of infection. The level of serum IFN-gamma correlated significantly with fecal oocyst shedding (r2 = 0.97) thereby establishing the importance of cell-mediated immunity in coccidia infection. Moreover, intestinal IFN-gamma levels increased sooner than those in sera (4 vs. 6 days post-infection) and both were observed prior to the appearance of parasite-specific antibodies (8 - 10 days post-infection), again indicating the importance of intestinal cellular immunity in coccidiosis. The relevance of this observation in the context of primary Eimeria infection is unclear since the coccidia parasites have reached the final stages of their life cycle by this time. These results thus demonstrate the importance of T cell immune responses against coccidia, characterized by local IFN-gamma secretion in the intestine in mediating host protective immune response to coccidia.