Eimeria coecicola Cheissin 1947: endogenous development in gut-associated lymphoid tissue.

Coccidia-free rabbits were inoculated with different doses of a pure strain of Eimeria coecicola and samples of gut were taken at 80, 96, 112, 128, 144, and 160 h postinoculation. The use of a very low infective dose (2-20 oocysts) was sufficient to study the last merogony. The number of merozoites in meronts increased when the infective dose decreased. Only the first merogony of this coccidium in lymphocytes or M-cells of gut-associated lymphoid tissue (GALT) has previously been described. Three other generations of meronts are described herein. All these endogenous stages were observed in the epithelium of the vermiform appendix, sacculus rotundus, and Peyer's patches, especially at the bases of the domes. However, in heavily infected tissues the gamonts were seen throughout the epithelium of the GALT. The third- and fourth-generation meronts were of two types. As in other eimerian species of the rabbit, type A meronts produced thick polynucleated merozoites, whereas type B meronts gave rise to large numbers of thin merozoites with one nucleus. Microgamonts were polynucleated and less numerous than macrogamonts. Type A meronts were also polynucleated and less numerous at the end of the merogony. Therefore, types A and B could correspond to a sexual phenotype differentiation occuring during the two asexual phases of multiplication.