Eimeria Parva

Synonyms: Eimeria galouzoi (pro parte).

Hosts: Sheep, goat, Rocky Mountain bighorn sheep, Barbary sheep (Ammotragus lervia), Siberian ibex (Capra ibex sibirica), roe deer.

Location: Schizonts are found thruout the small intestine, and gametes and gametocytes in the cecum, colon and small intestine.

Geographic Distribution: Worldwide.

Prevalence: This species is common in sheep, less common in goats. Christensen (1938a) found it in 50% of 100 sheep from Idaho, Maryland and Wyoming. Jacob (1943) found it in 52% of 100 sheep and 9% of 11 goats in Germany; he also found it in a roe deer. Balozet (1932) found it in 21% of 63 sheep and 22% of 41 goats in Tunisia. Svanbaev (1957) found it in 9% of 302 sheep in Kazakhstan.

Morphology: This species has been described by Kotlan, Mocsy and Vajda (1929), Balozet (1932) and Christensen (1938a). The oocysts are subspherical, ellipsoidal or spherical, 12 to 22 by 10 to 18 u with a mean of 16.5 by 14.1 u (Christensen) or 17.2 by 13.5 u (Balozet). Their length width ratio is 1.0 to 1.5 with a mean of 1.18 (Christensen). The oocyst wall is smooth, homogeneous, pale yellow to yellowish green, and composed of 2 layers of which the outer is half as thick as the inner; there is a heavy, black refraction line on each side of the inner layer, according to Christensen. According to Balozet, the wall appears to be lined by a membrane. The sporont is clear. A micropyle is absent; according to Christensen, the oocyst wall occasionally appears slightly paler at one end than the other. An oocyst polar granule and oocyst residuum are absent. The sporocysts are oval. The sporocyst residuum is indistinct if present at all. The sporulation time is 1 to 2 days (Christensen) or 7 to 8 days (Balozet).

Life Cycle: The life cycle of E. parva in sheep has been described by Kotlan, Pellerdy and Versenyi (1951). The schizonts are found thruout the small intestine. They measure up to 185 to 256 by 128 to 179 u and are easily visible to the naked eye as whitish bodies. They lie in the mucosa, usually near the surface but sometimes as far down as the muscularis mucosae. They invade endothelial cells and enlarge both the host cell and its nucleus enormously. They are surrounded by a rather thick layer of connective tissue which becomes thinner as they increase in size. Each schizont produced thousands of straight merozoites 10 to 12 u long.

Kotlan, Pellerdy and Versenyi (1951) also found a second, much smaller type of schizont in the small intestine. It occurred in the superficial epithelial cells, was 10 to 12 u in diameter and contained about 10 to 20 merozoites 2.5 to 3 u long. They were not sure, however, whether it was part of the life cycle of E. parva.

The sexual stages occur mostly in the cecum and colon and to a lesser extent in the small intestine. They are found in the epithelial cells and measure 15 to 19 by 10 to 16 u.

Pathogenesis: This species is apparently not very pathogenic. Most of the damage is caused by the sexual stages in the large and small intestines. In a lamb killed by Kotlan, Pellerdy and Versenyi (1951) 16 days after experimental infection, the contents of the cecum and colon were semifluid, dark and mixed with blood in places. The wall was thickened and its surface uneven and denuded of epithelium in places. By histologic examination of the cecum, it was found that the mucosa had been stripped from the glandular layer in places and the tissue had become necrotic and infiltrated with lymphocytes and neutrophiles but no eosinophiles. Sharply separated from these necrotic areas were other areas in which most of the epithelial cells contained microgametocytes, macrogametes or young oocysts.