Exogenous and endogenous stages of Isospora brachyrhynchi sp.n. (Protozoa: Eimeriidae) from the American crow Corvus brachyrhynchos Brehm

Crows were intubated with varying doses of sporulated oocysts of I. brachyrhynchi n.sp. from a naturally infected crow, and killed for necropsy at various hours postinoculation. Tissues were fixed in Bouin's fluid and processed for light microscopy. Sporulation of I. brachyrhynchi to typical isosporoid oocysts required 48-72 h at 21 +or- 1 degrees C. Sporulated oocysts were 20.4 x 18.9 micro m, with sporocysts 16.2 x 10.6 micro m and sporozoites 12.9 x 2.6 micro m. There was a prominent polar granule within the oocyst and a Stieda body at the blunt end of the sporocyst. Each sporozoite had a central nucleus and 2 refractile granules. I. brachyrhynchi developed below the nuclei of epithelial cells in the small intestine. First-generation merogony occurred 24 h postinoculation in villar epithelium in the distal small intestine and occasionally in the lamina propria. Second-generation merogony occurred 72-96 h postinoculation in crypt epithelium of the distal small intestine. Gametogony occurred 96 h postinoculation, primarily in villar epithelium, throughout the length of the small intestine. The prepatent period was 5 days and the patent period was long (up to 3.5 months)..