Etiology and Transmission
Sarcocystosis, also known by the obsolete term sarcosporidiosis, is caused by intracellular parasites of the genus Sarcocystis. The species of greatest medical importance are S. bovihominis and S. suihominis.
The definitive host in the life cycle of these protozoa is the human. Intermediate hosts are agricultural animals, namely cattle and pigs. The mechanism of human infection is exclusively alimentary. Infection occurs through the consumption of beef or pork that has not undergone adequate thermal processing and contains specific tissue forms of the parasite. The name of the pathogen derives from the Greek root sarc-, meaning "meat," reflecting the primary transmission route of the infection.
Intestinal Phase of Development
Upon entering the human gastrointestinal tract with infected meat, sarcocysts rupture, releasing numerous merozoites. These cells feature a pointed anterior end, which facilitates their invasion of host epithelial cells. Merozoites localize within the villi of the small intestine mucosa, where sexual reproduction, termed gametogeny, is initiated.
During this process, gamete fusion (copulation) occurs, resulting in the formation of oocysts. Sporocysts gradually develop inside the oocysts. A characteristic feature of sarcocystosis is that fully mature sporocysts (or oocysts containing them) are excreted into the external environment with human feces. The diagnostic stage is an oval sporocyst, measuring 10 to 16 µm, containing exactly four mature sporozoites.
Tissue Phase of Development
In addition to the intestinal cycle, the parasite can undergo a tissue phase of development. Sporozoites can enter the bloodstream and migrate hematogenously from the intestine to muscle tissue. Once in the muscles, the protozoa initiate asexual reproduction, known as merogony (or schizogony).
The result of this reproduction is the formation of sarcocysts within muscle fibers. These are elongated structures that can reach up to 5 centimeters in length. Externally, they are covered by a thin membrane, and their internal content consists of a vast number of merozoites. In this form, the parasite persists in the tissues of the intermediate host.
Clinical Manifestations, Diagnosis, and Treatment
The course of sarcocystosis is frequently asymptomatic or presents with non-specific signs. Two main forms of the pathology are distinguished:
- Intestinal form: accompanied by dyspeptic disorders (digestive disturbances).
- Muscular form: may be occult, though in some cases it provokes muscle inflammation (myositis) and skin rashes.
Microbiological diagnosis relies on microscopic examination of smears from freshly passed feces. Preparations are stained with Lugol's iodine solution. It is important to note that sporocysts are detected in the stool only 9 days post-infection. In the muscular form, a histological method is used—microscopic examination of biopsy samples taken directly from the lesion sites.
Treatment strategy for sarcocystosis is predominantly supportive (symptomatic therapy). In cases of acute infection, the antibacterial drug furazolidone is prescribed. Prevention measures are entirely analogous to those used for toxoplasmosis prevention: strict hygiene and thorough thermal processing of meat products before consumption.