Control of coccidiosis: lessons from other sporozoa.

Coccidiosis is the most important parasitic infection in poultry worldwide and also causes problems in cattle, sheep and goats. Control is largely limited to good husbandry and prophylactic chemotherapy using a range of drugs against which resistance is rapidly acquired. Attempts at vaccination using conventional vaccines have been disappointing and there is now a need for a new approach. Research into the immunology of coccidiosis has lagged behind that of other sporozoans and there are useful lessons that might be learned from studies on toxoplasmosis, cryptosporidiosis, theileriosis and malaria. In these infections the emphasis has turned to the cytokine network that drives the response towards protection. Central to these studies are the roles of interferon-gamma, interleukin-12 and activated macrophages with the involvement of nitric oxide in parasite killing. Cytotoxic T cells have also increasingly been implicated. Research has shown that different immune responses can be elicited by manipulating the cytokine system and these new concepts can be applied to the design of peptide or recombinant vaccines, and the possibilities of developing such vaccines against coccidiosis will be discussed.