Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 7, 1999
Publication Date: N/A
Interpretive Summary: Sarcocystis falcatula is a pathogenic protozoan parasite of birds transmitted via the feces of infected opossums. There are numerous reports of fatal sarocystosis in passerine birds, especially in zoos in the U.S. Recently, the parasite has been confused with a related species, Sarcocystis neurona also found in opossum feces. Scientists at the Beltsville Agricultural Research Center and Montana State University describe the ultrastructure of Sarcocystis falcatula in bird tissues and differentiate it from Sarcocystis neurona. These results will be of use to parasitologists and veterinary pathologists.
Transmission electron microscopy was used to study the ultrastructure of schizogony Sarcocystis falcatula in the lungs of budgerigars (Melopsittacus undulatus). Schizogony occurred exclusively by endopolygeny within endothelial cells of pulmonary capillaries, venules, and small veins. Early schizonts were elongate with a large nucleus and nucleolus, surrounded by a pellicle consisting of a plasmalemma and an inner single membrane, and contained most of the organelles and inclusion bodies found in merozoites of Sarcocystis species. As development proceeded, schizonts increased in size and conformed to the shapes of the pulmonary blood vessels. As micronemes, dense granules, the conoid, and subpellicular microtubules diappeared, there was an increase in the size and number of mitochondria, Golgi complexes, and Golgi adjuncts (apicoplasts). As the nucleus elongated, there was a progressive increase in the number of spindles located at various intervals along the nuclear envelope. Eventually, 2 merozoites formed internally immediately above each spindle. During endopolygeny, a portion of the nucleus was incorporated into each merozoite bud along with 1 or 2 Golgi adjuncts, a Golgi complex, mitochondria, endoplasmic reticulum, and ribosomes. During merozoite formation, micronemes appeared in close association with the Golgi complex and gradually increased in number. The pellicle invaginated around the merozoites so they budded at the schizont surface leaving behing a small, central residual body. Dense granules appeared after merozoites were completely formed. Schizonts were 24 x 6.8 æm and contained 24-96 merozoites. Merozoites were 5.1 x 1.8 æm and were found free in the pulmonary air passages and pulmonary capillaries, and within nearly all