The endogenous development of the rabbit coccidium Eimeria exigua Yakimoff, 1934

The coccidium Eimeria exigua from the tame rabbit (Oryctolagus cuniculus) has been neglected so far since it was considered to be an invalid species. Indeed, little is known about this coccidium. We have studied its endogenous development in domestic rabbits by means of light and electron microscopy. The first meronts appeared 72 h post-inoculation (h.p.i.), but a total of four asexual generations developed from 72 to 144 h.p.i. Meronts and gamonts were localized in the small intestine and the asexual stages successively moved from the duodenum to ileum. All parasite stages were found exclusively in the epithelium of the walls and tops of the villi. Two types of meronts developing in parallel during the asexual phase were observed from at least the 2nd generation. As in other rabbit coccidia, these forms corresponded to type A, which usually develops two polynucleate merozoites where endomerogony occurs, and type B, characterized by more numerous uninucleate merozoites arising by ectomerogony. This report is the first description of the endogenous stages of E. exigua.