| Popis: |
Although many workers have commented on the invasive powers of the sporozoites of coccidia, no formal studies have been made on this subject. Fantham (1910) discussed the penetration of the sporozoites of Eimeria avium in the young grouse, while Hadley (1911) commented upon the rapidity of the penetration of epithelial cells by the sporozoites of E. avium (= tenella). He noted that free sporozoites penetrated the epithelial cells at once. Tyzzer, Theiler and Jones (1932) indicated that the sporozoites of E. necatrix invaded the epithelium immediately after being freed from the oocyst, while the sporozoites of E. tenella probably took longer; for they found live sporozoites free in the cecal content 24 hours after the chicken was infected. Tyzzer et al, as well as Edgar (1949), reported that sporozoites of both species invaded the epithelium of the gland fundi. These workers, like Hadley (1917), stated that the sporozoites occasionally passed through the epithelium and parasitized the cells of the underlying tissue. The sporozoites of E. praecox were observed in the tunica propria by Tyzzer et al, but there was no evidence of further development. The recognition of the early schizonts of E. bovis in the endothelial cells lining the lacteals suggests that these sporozoites passed through the epithelium of the intestinal wall (Hammond et al, 1946). The sporozoites of E. brunetti were observed by Boles and Becker (1954) in the cores of the villi 3 hours after the chicken was infected. Further comments on the penetration of E. tenella sporozoites were made by Scholtyseck (1953), who observed that sporozoites were liberated from the oocysts between 12 and 24 hours after infection, but he did not arrive at a decision concerning the manner in which the sporozoites reached the submucosal cells of the ceca. He thought that they penetrated directly from the cecal lumen into the epithelial cells, then passed from the crypts of Lieberkiihn into the tunica propria, invaded the fibrocytes of the fibrous connective tissue, and developed into schizonts. Greven (1953) reported the presence of sporozoites of E. tenella in the epithelial cells of the crypts 32 hours after infection, but on the third day she observed them in fibrocytes. |
