Host-parasite interactions of apicomplexan parasites with their vertebrate hosts

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Many of apicomplexan parasites (such as malaria, Toxoplasma and coccidia) are of serious veterinary, agricultural and medical importance. Eimeria are continuing and serious challenges to profitable rearing of commercial poultry (especially chickens). Medication costs and production losses from coccidiosis cost the poultry industry several $100 million each year in Canada. Live vaccines against coccidia are possible but are complicated by immunologically distinct strains of many Eimeria species and alteration to the intestinal tract that can predispose chickens to bacterial disease (esp. necrotic enteritis). We have distinct lines of E. maxima that are similar to one another but do not cross-immunize birds (they do not protect against challenge with the second strain despite their similarity). The few differences that exist between these E. maxima strains must be important targets of a protective immune response. The strains will continue to be dissected at the molecular level to identify unique molecules in each strain that may represent immunologically important antigens that the chickens use to protect themselves against challenge; this hypothesis will be tested once the unique molecules have been isolated. This is critical for the generation of non-viable vaccines against coccidia. Second, the immune responses of birds will be examined when infected with one strain of the parasite and then challenged with the second strain. To address the limitations of live vaccines in broiler chickens (because of an altered gut environment that promotes serious bacterial enteritis), probiotic bacteria (harmless, beneficial commensal bacteria isolated from chickens) will be tested for their ability to protect the intestinal tract of birds during live coccidial vaccination. If proven, this method could radically reduce our reliance on in-feed drugs currently employed to control these parasites in meat birds. Finally, in other work, we hope to better understand the evolutionary relationships that exist among all parasites of the phylum Apicomplexa. In addition to better understanding our biological world, characterizing poorly known parasites will give us a way to predict likely life cycles, potential hosts and possible drug sensitivities for agents of emerging parasitic disease.