Exogenous stages of Isospora serini (Aragão)and Isospora canaria sp. n. in the canary (Serinus canarius Linnaeus).

Exogenous stages of Isospora serini (Aragao) and Isospora canaria sp. n. from the canary (Serinus canarius Linnaeus) are described. Oocytes of I. serini are spheroid and average 19.2 times 20.1 mum, while those of I. canaria are larger, more ellipsoid, and average 21.8 times 24.6 mum. No oocyst residuum is present and the oocyst walls of both species are colorless, transparent, and single layered. Sporocysts average 9.4 times 15.2 mum for I. serini and 11.5 times 18.1 mum for I. canaria. The I. canaria sporocyst has a substiedal body, but none was found in I. serini sporocysts. Both species have a spherical sporocyst residuum; this was obscured in the I. serini sporocyst by scattered granules. Living sporozoites of I. canaria average 3.6 times 16.9 mum and have 1 to 3 refractile globules; those of I. serini have 2 globules and average 2.8 times 12.6 mum. A disseminated infection of the mononuclear phagocytes results from administration of I. serini while I. canaria oocysts give rise to a typical coccidian infection restricted to the intestinal epithelium. Asexual stages of I. serini in macrophages are indistinguishable from parasites previously called avian Toxoplasma, Atoxoplasma, and Lankesterella.