Sarcocystis is a genus of parasites, the majority of species infecting mammals, and some infecting reptiles and birds.
The life-cycle of a typical member of this genus involves two host species, a definitive host and an intermediate host. Often the definitive host is a predator and the intermediate host is its prey. The parasite reproduces sexually in the gut of the definitive host, is passed with the feces and ingested by the intermediate host. There it eventually enters muscle tissue. When the intermediate host is eaten by the definitive host, the cycle is completed. The definitive host usually does not show any symptoms of infection, but the intermediate host does.
There are about 130 recognized species in this genus. Revision of the taxonomy of the genus is ongoing, and it is possible that all the currently recognised species may in fact be a much smaller number of species that can infect multiple hosts.
The name Sarcocystis is dervived from Greek: sarx = flesh and kystis = bladder.