Location: Anterior small intestine, occasionally middle and lower small intestine or even tubular part of ceca.
Geographic Distribution: Worldwide.
Morphology: The oocysts are subspherical, smooth, colorless, 10 to 21 by 9 to 18 u with a mean of 16 by 13 u. A micropyle is absent. An oocyst polar granule is present. An oocyst residuum is absent. The sporocysts are ovoid, 10 by 6 u, with a Stieda body, but without a sporocyst residuum. The sporulation time is 2 days. Edgar (1955) found some infective oocysts as early as 18 hours at 29° C.
Life Cycle: The life cycle of this species has been studied by Tyzzer (1929) and Joyner (1958), the latter using a strain derived from a single oocyst. The endogenous stages occur in the epithelial cells of the villi and occasionally in the glands. They lie against the host cell nuclei, and below them more often than above according to Tyzzer. However, Joyner stated that the schizonts are nearly always superficial; he illustrated the sexual stages as below the host cell nuclei. The schizonts produce 6 to 24 or rarely 30 merozoites, but the number of schizont generations is not known. The merozoites are crescentshaped, with blunt ends, and measure about 5 by 1.5 u.
The microgametocytes are about 9 to 14 u, long and the macrogametes are somewhat larger. In contrast to most other coccidian species, in which development following a single inoculum is quite synchronous, both asexual and sexual stages occur together. The prepatent period is 4 to 5 days, and the patent period 10 days (Joyner, 1958).
Joyner (1958) found that chicks infected with 1000 oocysts produced 61,709 oocysts per oocyst fed, while chicks fed 100,000 oocysts produced 2253 oocysts per oocyst fed.
Pathogenesis: This species is slightly pathogenic, but is unlikely to be of pathological significance under normal field conditions. Tyzzer (1929) observed neither signs nor gross lesions in young chickens given tremendous and repeated doses of sporulated oocysts. Becker (1959) found neither lesions nor diarrhea in infected chickens. Joyner (1958) found that weight gains of 6- to 26-day-old birds fed 500,000 oocysts were reduced, while 38% of 29 6-day-old chicks died after being fed 2.5 million oocysts.