Pathogenesis of Sarcocystis falcatula in the budgerigar. I. Early pulmonary schizogony.

Sarcocystis falcatula is a protozoan parasite which obligatorily alternates its definitive host, the opossum (Didelphis virginiana), and a uniquely wide range of avian intermediate hosts. The disease produced by this coccidian parasite in intermediate hosts was studied in the budgerigar bird (Melopsittacus undulatus). The ultrastructure of pulmonary sporozoites, meronts and merozoites of this Sarcocystis species is described. Early schizogony occurs progressively in pulmonary capillary and in venular and venous endothelial cells.