Experimental tracheal and conjunctival infections with Cryptosporidium sp. in pigs.

Tracheal and conjunctival infections with Cryptosporidium were established in pigs by inoculation of oocysts into the trachea and onto the conjunctival sacs. The protozoa were found attached to epithelial cells by an electron-dense band and a folded, vacuolated feeder organelle. They were situated in a parasitophorous vacuole surrounded by a double-layered membrane covered by glycocalyx. Trophozoites, schizonts, merozoites, macrogametes and oocysts could be demonstrated. In addition to normal stages of the life-cycle, degenerate stages were found. The infections with Cryptosporidium were characterized by focal destruction and loss of epithelial cells. Numerous intraepithelial lymphocytes were associated with affected foci, as were infiltrations with lymphocytes, monocytes, and macrophages.