| Abstract: | SYNOPSIS. Cell lines of embryonic lamb trachea (LETr), lamb thyroid (LETh), and bovine liver (BEL) as well as an established cell line of Madin-Darby bovine kidney (MDBK) were used in a study of the in vitro development of Eimeria crandallis from sheep. Excysted sporozoites were inoculated into Leighton tubes containing coverslips with monolayers of the different cell types. Coverslips were examined with phase-contrast and interference-contrast at various intervals up to 20 days after inoculation; thereafter the monolayers were fixed and stained in various ways. Freshly excysted sporozoites, with 2–10 spheroidal refractile bodies, entered all of the cell types in relatively small numbers; intracellular sporozoites were first seen 2 min after inoculation. After 24 hr, most intracellular sporozoites had only 1 or 2 refractile bodies. Before and during transformation of sporozoites, the nucleus and peripheral nucleolus increased markedly in size. Transformation resulted in usually spheroid but sometimes ellipsoid trophozoites. Trophozoites were seen first 3–4 days, and binucleate schizonts at 4–5 days after inoculation. Immature schizonts increased considerably in size and eventually had large numbers of nuclei. Some of the parasites became lobulated and the lobules often separated to form individual schizonts. In BEL, LETr and LETh cells, mature schizonts, up to 150 μm in diameter, were seen first 11–14 days after inoculation. The BEL cells were the most favorable for development. Merozoites were formed by a budding process from the surface of the schizonts as well as from blastophores. Some merozoites were seen leaving mature schizonts, but no further development was observed. Merozoites frequently were motile and had a sharply bent posterior end. Marked nuclear and cytoplasmic changes were observed in parasitized cells. |
