Life Cycles of Two Isospora Species in the Canary,Serinus canarius Linnaeus*

SYNOPSIS. The endogenous stages of Isospora serini Aragão and Isospora canaria Box are described from experimentally infected canaries, Serinus canarius Linnaeus. Unlike other Coccidia, the first part of the I. serini life cycle takes place in mono-nuclear phagocytes. Five asexual generations are described from this cell type; 2 additional asexual generations and the sexual stages take place in the intestinal epithelium. Isospora canaria, on the other hand, has a conventional coccidian life cycle in that all of the endogenous stages are in the epithelium of the small intestine, with 3 asexual generations and the sexual generation described in the duodenal epithelium. The 2 species differ in their position relative to the nucleus of the intestinal epithelial cell. Isospora serini is usually on the lumenal side of the nucleus while I. canaria is below the nucleus, toward the basement membrane. The prepatent period is 4–5 days for I. canaria and 9–10 days for I. serini. Patency lasts for 11–13 days in I. canaria infections, but duration of oocyst output is more chronic in I. serini infections, persisting for as long as 231 days. Both species have a diurnal periodicity of oocyst discharge which occurs in late afternoon and evening.