Immunological aspects of infections with Eimeria maxima: A short review

Eimeria maxima is one of the seven species of protozoan parasites that cause intestinal coccidiosis in chickens. Discovered and first described exactly 70 years ago, the parasite has some unique features that both distinguish it from the other members of the genus and make it of relevance to the world's poultry industry. Of special interest is the balanced immunological relationship that E. maxima achieves with its host. The marked immunogenicity of the parasite results in swift and complete protection to homologous challenge, but is counterbalanced by the ubiquity of antigenically different strains that provide a significantly heterologous challenge and are only poorly controlled-essentially two sides of the same coin. In this paper, we will describe some of the features of the biology of E. maxima, with an emphasis on the immunogenicity and antigenic diversity of the parasite, and discuss some of the ways in which these features impinge on attempts to control infection. The review is, of necessity, brief and selective by choice; for more information, the reader is referred to the definitive paper on E. maxima by Tyzzer (1929) and to reviews on other aspects of Eimeria spp., including E. maxima, by Rose (1997) and Chapman (1997).