Life Cycle of Eimeria krijgsmanni-Like Coccidium in the Mouse (Mus musculus)

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Life cycle of Eimeria krijgsmanni-like coccidium isolated from the feces of naturally infected mice purchased from commercial sources was examined. The parasite was purified by single oocyst isolation and maintained by passage in the mice before experiments. The sporulated oocysts were ovoid or ellipsoid, measuring 19.3 × 14.8 μm on average. One or two small polar granules were present. Micropyle and oocyst residuum were absent. Sporocysts were ellipsoid, measuring 11.6 × 7.2 μm on average with a small Stieda body and sporocyst residuum. Six groups of respective 5 mice (4-week-old) were inoculated with doses varying from 2.0 × 10¹ to 10⁶ oocysts. All the mice examined began to shed oocysts from 7 day postinoculation (PI) and their maximum number of oocysts per gram of feces were 10⁶ on day 8 PI. Patency was 6 or 7 days. This parasite had severe virulence to the mice that is, the mice given 10⁶ oocysts showed anorexia, diarrhoea and rough hair from 1 day and all of them died on day 3 PI. The mice given 10³ or more oocysts showed the clinical signs described above from day 5 and 4 of them received 10⁵ died on day 9 or 10 PI. The parasites occurred within the epithelial cells of cecum, colon and rectum of infected mice. Sporozoites, 13.9 × 3.0 μm, with two large refractil bodies on side of the nucleus located subcentrally were observed on day 1 and 2 PI. Merozoites were first observed at 24 hr PI, and sexual stages were found from 4 day PI. No parasites were detected in the small intestine and mecenteric lymph nodes.