Hosts: Domestic and wild turkey.
Altho Steward (1947) and Gill (1954) claimed to have transmitted this species experimentally to the chicken, Tyzzer (1929) was unable to transmit it to the chicken, ring-necked pheasant or bobwhite quail, Hawkins (1952) was unable to transmit it to the bobwhite quail or Hungarian partridge, and Moore, Brown and Carter (cited by Moore, 1954) and Clarkson (1959a) were unable to transmit it to the chicken.
Location: The first generation schizonts, which are relatively few in number, are found only in the small intestine a short distance on either side of the yolk stalk. They lie below the host cell nuclei in the epithelial cells, mostly in those near the base of the villi but not in the deep glands.
The second generation schizonts occur in the cecum, where they lie above the host cell nuclei in the epithelial cells of the tips of the villi.
The sexual stages are found in the cecum, rectum and, to a slight extent, ileum. They lie above the host cell nuclei deep in the glands of the cecum as well as in the surface epithelium (Clarkson, 1959a).
Geographic Distribution: Worldwide.
Prevalence: Common. Kozicky (1948) found "E. meleagridis" in the droppings of 40% of 95 wild turkeys in Pennsylvania.
Morphology: This species was first described by Tyzzer (1927). The oocysts are ellipsoidal, smooth, 19 to 31 by 14 to 23 u with a mean of 24 by 17 u. The oocysts measured by Clarkson (1959a) were 22.5 ± 2. 3 by 16.25 ± 1.23 u. A micropyle is absent. One or 2 oocyst polar granules are present. An oocyst residuum is absent. The sporocysts are ovoid, with a Stieda body. A sporocyst residuum is present. The sporulation time is 1 day. Edgar (1955) found some sporulated oocysts as early as 15 hours at 28° C.
Life Cycle: Hawkins (1952) and Clarkson (1959a) described the life cycle, the latter using a strain which he had derived from a single oocyst. The first generation schizonts are present 2 to 5 days after infection, being found in greatest numbers at 60 hours. They measure 20 by 15 u and contain 50 to 100 merozoites measuring 7 by 1.5 u. The second generation schizonts first appear 60 hours after infection, and mature ones are present after 70 hours; they are seen in greatest numbers at 84 hours. They are about 9 u in diameter and contain 8 to 16 merozoites which measure 10 by 2 u. Hawkins stated that there may be a third asexual generation, but that most of the second generation merozoites develop into sexual stages; Clarkson did not describe third generation schizonts.
Macrogametes and microgametocytes appear at 91 hours and become mature 9 days after infection. They measure about 18 by 13 u. The microgametes are biflagellate.
According to Hawkins, oocysts appear in the feces 5 days after infection; Clarkson found that the prepatent period was 108 to 112 hours.
Pathogenesis: This species is practically non-pathogenic. Hawkins (1952) observed only a slight drop in weight in poults experimentally infected with 400,000 to 1 million sporulated oocysts. Moore and Brown (1951) infected poults with "enormous numbers" of fresh, sporulated oocysts without producing clinical evidence of coccidiosis. Clarkson (1959a) found that doses of up to 1 million oocysts produced no signs of disease in 2-week-old poults.
The serosal surface of the ceca of heavily infected birds is cream colored. The ceca contain a non-adherent, mucoid or caseous, yellow plug on the 5th and 6th days. Caseous material composed of oocysts and epithelial cells is sometimes found in the feces on the 6th day, but the ceca appear quite normal in another day or two. Hawkins noted petechial hemorrhages in the cecal mucosa.
Immunity: Turkeys which have recovered from an infection with E. meleagridis have a high degree of immunity according to Hawkins (1952). Clarkson (1959a) found no cross immunity between this species and E. adenoeides.