Life cycle studies with Eimeria magna Pérard, 1925

Excystation of Eimeria magna required exposure to CO2 at body temperature followed by trypsin and bile. Incubation in the presence of CO2 produced marked effects on the inner layer of the oocyst wall. The evidence suggests that CO2 stimulates enzymic activity from within the oocyst rather than exerting a physico-chemical effect on the oocyst wall from the outside. Released sporozoites measured 19.65 X 3.33 mum. In the rabbit, E. magna undergoes at least 5 cycles of asexual schizogony before gametogony takes place. First-generation schizonts were observed at 30 hr, measured 15 X 11 mum and contained 4, 6, 8 or occasionally 12 merozoites; the merozoites were characterised by two very large and prominent refractile granules. As the infection progressed, schizont size and merozoite numbers became more variable; some schizonts contained 2-8 fat merozoites, many probably multinuclear, while other schizonts contained 12-100 thinner merozoites. First generation schizogony took place in the glands; all subsequent stages developed in the upper parts of the villi of the small intestine. Sexual forms have been seen as early as 96 hr, but maximum sexual activity was noted at 120-192 hr. Oocysts measured 35.87 X 24.05 mum. The first oocysts were passed 6-7 days after inoculation, with peak production at 8-9 days. Sporulation was optimal at 30 degrees C; higher temperatures inhibited sporulation, and were in time lethal, while sporulation would take place normally after suppression by cold for at least 11 months. Single oocyst inoculations indicated a maximum reproductive potential of 26.15 million. Pathogenic effects were mostly mild, amounting to growth depression over days 4-7 and softening of the faeces; occasionally diarrhoea and/or death occurred.