SARCOCYSTIS NEURONA (PROTOZOA: APICOMPLEXA): DESCRIPTION OF OOCYSTS, SPOROCYSTS, SPOROZOITES, EXCYSTATION, AND EARLY DEVELOPMENT

• Published in: The Journal of parasitology 2004-06, Vol.90 (3), p.461-465
• Main Authors: Lindsay, David S, Mitchell, Sheila M, Vianna, M. C, Dubey, J. P
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; biological development; Cell culture; Cell culture techniques; Cell Line; Cercopithecus aethiops; Development; DEVOLOPMENT; Electrons; excystation; Fundamental and applied biological sciences. Psychology; General aspects; General aspects and techniques. Study of several systematic groups. Models; Globules; Granular materials; Horse Diseases - parasitology; Horses; Intermediate hosts; Intestine; Invertebrates; Microscopy, Electron - veterinary; Microscopy, Electron, Scanning - veterinary; Muscles; Neurological diseases; Oocysts; Opossums - parasitology; Organelles; Parasite hosts; Parasitology; Plates; Protozoa; Raccoons; Residuums; Sarcocystis - growth & development; Sarcocystis - physiology; Sarcocystis - ultrastructure; Sarcocystis neurona; Sarcocystosis - parasitology; Sarcocystosis - veterinary; Scanning electron microscopy; Schizogony; Schizonts; Skeletal muscle; Sporocysts; sporocysts (Protozoa); Sporozoites; Thin films; Transmission electron microscopy; ultrastructure; Veterinary medicine
• ISSN: 0022-3395; 1937-2345
• DOI: 10.1645/GE-230R

Equine protozoal myeloencephalitis is a major cause of neurological disease in horses from the Americas. Horses are considered accidental intermediate hosts. The structure of sporocysts of the causative agent, Sarcocystis neurona, has never been described. Sporocysts of S. neurona were obtained from the intestines of a laboratory-raised opossum fed skeletal muscles from a raccoon that had been fed sporocysts. Sporocysts were 11.3 by 8.2 μm and contained 4 sporozoites. The appearance of the sporocyst residuum was variable. The residuum of some sporocysts was composed of many dispersed granules, whereas some had granules mixed with larger globules. Excystation was by collapse of the sporocyst along plates. The sporocysts wall was composed of 3 layers: a thin electron-dense outer layer, a thin electron-lucent middle layer, and a thick electron-dense inner layer. The sporocyst wall was thickened at the junctions of the plates. Sporozoites were weakly motile and contained a centrally or posteriorly located nucleus. No retractile or crystalloid body was present, but lipidlike globules about 1 μm in diameter were usually present in the conoidal end of sporozoites. Sporozoites contained 2–4 electron-dense rhoptries and other organelles typical of coccidian zoites. Sporozoites entered host cells in culture and underwent schizogony within 3 days.