Sarcocystis

Abstract

Sarcocystis (derived from the Greek words sarx, which means flesh, and kystis, which means bladder) are apicomplexan protozoans that cause sarcocystosis or sarcocystiosis. Infections are characterized by the formation of numerous sarcocysts, which are essentially parasite-full sacs ranging in size from micrometers to several centimeters, in the muscles or nervous tissue of a great variety of animals. The genus is composed of more than 100 species that differ in pathogenicity, host specificity, and sarcocyst structure and location. Sarcocystis are obligatory intracellular, with a typical coccidian life cycle, consisting of merogony, gametogony, and sporogony. The life cycle involves an intermediate and a definitive host, usually an herbivore and a carnivore, respectively. At first, a series of asexual reproduction steps culminate with sarcocyst formation. Ingestion of cyst-infected tissues by the definitive host leads to sexual reproduction of the parasite in the digestive tract, followed by excretion of infective forms in the feces. The cycle is closed when an intermediate host becomes infected by the fecal-oral route. Most Sarcocystis are species-specific for intermediate and family-specific for definitive hosts. Infection of farm animals is sometimes associated with the reduction in quality and quantity of meat, wool, and fiber, resulting in important economic losses. Additionally, some Sarcocystis species are zoonotic. Thus, the study of sarcocystosis constitutes an active field of research.