Location: Upper third of small intestine.
Geographic Distribution: Probably worldwide.
Morphology: The oocysts are ovoid, smooth, colorless, 20 to 25 by 16 to 20 u with a mean of 21 by 17 u. A micropyle is absent. An oocyst polar granule is present. Oocyst and sporocyst residua are absent. The sporulation time is 2 days.
Life Cycle: Tyzzer, Theiler and Jones (1932) studied the life cycle of this species. The endogenous stages occur in the epithelial cells of the villi, usually along the sides of the villi and below the host cell nuclei. There are 2 generations of schizonts, the second of which appears as early as 32 hours after infection. Later development is irregular, both sexual and asexual stages being seen together. The prepatent period is 4 days, and the patent period is short, 4 days or a little more in the absence of reinfection.
Pathogenesis: This species is essentially non-pathogenic. Tyzzer, Theiler and Jones (1932) were unable to cause death with heavy doses of oocysts, altho they did observe a mucous cast containing large numbers of oocysts at the end of the infection. Becker (1959) found that E. praecox is probably no more pathogenic than E. mitis.