Hosts: Domestic goose, blue goose (Anser caerulescens), Richardson's Canada goose (Branta canadensis hutchinsi).
Location: Small intestine, mainly posterior part.
Geographic Distribution: Europe, North America.
Prevalence: E. anseris has been reported from domestic geese only in Europe (Kotlan, 1933; Cerna, 1956) and is apparently not particularly common there. Hanson, Levine and Ivens (1957) found it in 4% of 73 blue geese from Ft. Severn and Weenusk, Ontario and in 33% of 6 Richardson's Canada geese from York Factory, Manitoba.
Morphology: This species was described in detail by Hanson, Levine and Ivens (1957). The oocysts have the form of a sphere surmounted by a truncate cone, with a micropyle at the truncate end, and measure 20 to 24 by 16 to 19 u with a mean of 22 by 17 u (16 to 23 by 13 to 18 u according to Kotlan, 1933). The oocyst wall is smooth, colorless, composed of a single layer about 1 u thick, and slightly thickened around the micropyle but incised sharply to form a plate or shelf across the micropyle itself. The oocyst residuum is a mass of amorphous material just beneath the micropyle and forming a seal beneath it. An oocyst polar granule is absent. The sporocysts are ovoid and almost completely fill the oocyst. The sporocyst wall is slightly thickened at the small end. The sporocysts are 10 to 12 by 7 to 9 u. A sporocyst residuum is present. The sporozoites often lie more or less transversely at the anterior and posterior ends of the sporocyst. The sporulation time is 1 to 2 days according to Kotlan (1933).
Life Cycle: The endogenous stages have been described by Kotlan (1933). They occur in compact clumps under the intestinal epithelium near the muscularis mucosae and also in the epithelial cells of the villi. The schizonts are spherical, 12 to 20 u in diameter, and contain 15 to 25 slightly curved, crescent-shaped merozoites. There is probably only a single asexual generation. The sexual stages are found mostly in the subepithelial tissues of the villi, but invade the epithelium in heavy infections. The macrogametes measure 12 to 16 by 10 to 15 u. The microgametocytes are spherical and about the same size. Oocysts first appear in the feces 7 days after infection, and the patent period is 2 to 8 days.
Pathogenesis: Kotlan (1933) reported that experimental infections in 2.5- to 3-month-old geese were harmless, but described two outbreaks of intestinal coccidiosis in goslings which he considered due to a combination of E. anseris and E. nocens.