Immunology of Giardia and Cryptosporidium infections.

Giardiasis and cryptosporidiosis occur in immunocompetent persons, and as opportunistic infections in immunocompromised individuals. The causative organisms of giardiasis (Giardia lamblia) and cryptosporidiosis (Cryptosporidium parvum) have markedly different life cycles, but currently available evidence suggests that intestinal antibody plays a major part in host protection against both parasites. In the case of G. lamblia, the evidence points to a role for intestinal antitrophozoite antibody in blocking adherence of trophozoites to intestinal epithelium, with consequent removal of trophozoites from the intestine by peristalsis. Similarly, recent work supports the view that C. parvum infection can be prevented or interrupted by antibody that binds to Cryptosporidium life cycle stages present in the intestinal lumen (sporozoites and merozoites). Molecular characterization of G. lamblia and C. parvum immunodominant antigens would facilitate future studies aimed at determining whether vaccination against giardiasis or cryptosporidiosis is feasible.