MIGRATION OF SPOROZOITES AND MEROGONY OF EIMERIA-COECICOLA IN GUT-ASSOCIATED LYMPHOID-TISSUE

The invasive phase of Eimeria coecicola was studied during the first 8 0 h postinoculation (p.i.). Using a method that synchronized the life cycle, sporozoites were observed in the duodenum and the jejunum until 32 h p.i. They were seen first in the villous epithelial cells or in host cells resembling intraepithelial lymphocytes (IEL). Later they we re observed in IEL in the lamina propria. After 48 h p.i., no coccidia n stage was identifiable in the mucosa of the small intestine but spor ozoites appeared in the lymphoid cells of lymphatic follicles of the g ut-associated lymphoid tissue (vermiform appendix, sacculus rotundus, and Peyer's patches). The first merogony was observed 64 h p.i. in the se lymphoid cells and in membranous epithelial cells (M-cells) but was never seen in the epithelium itself. Morphologically there were two t ypes of meronts, depending on the host cell type, but in both cases th e merozoites contained a refractile body and resembled sporozoites. Th e first meronts of the second generation were observed 80 h p.i. in th e villous epithelial cells of the domes of the follicles of the gut-as sociated lymphoid tissue, where the further development of this Eimeri a takes place. This pattern of invasion strongly suggests that sporozo ites take an exclusively extraintestinal route to reach the target cel ls. Moreover, to our knowledge this is the first description of an eim erian merogony that does not take place in epithelial cells.