Scanning electron microscopy of merogonous stages of Eimeria falciformis var. pragensis in Mus musculus.

Asexual stages of Eimeria falciformis var. pragensis in Swiss-Webster mice were studied by scanning electron microscopy. Sporozoites were present in the cecum and colon 2 h post-inoculation (PI) and measured 11.3 X 2.1 micrometer (9-13.9 X 2-2.2 micrometer). Sporozoites penetrated epithelial cells with an extended anterior end and were constricted at the site of entry. Asexual generations were found in the cecum and colon epithelial cells. In meronts found at days 3-9 PI, merozoites matured synchronously, were oriented in the same direction, and were arranged in a helical pattern. Such meronts measured 11.3 X 6.4 micrometer (8-13.7 X 5-7.4 micrometer) and contained 8-12 merozoites, which measured 11.9 X 1.5 micrometer (7.4-15.7 X 1.3-1.8 micrometer). Meronts which were present at day 7 PI measured 9.5 X 8.2 micrometer (9-10.5 X 7-9.5 micrometer) and contained 20-50 small merozoites which budded asynchronously from a central residuum. At days 3-7 PI, parasitized epithelial cells had shorter and fewer or no microvilli. The lumenal plasmalemma of the host cell was often disrupted or absent in cells containing mature meronts and escaping merozoites. At day 6 PI, phagocytic cells appeared on the epithelial surface, some of which were in contact with merozoites. Small foci of exposed basal lamina were present at day 7 PI in areas where cells had sloughed from the epithelium.