Causative agent: Sarcocystis spp
The life cycle of sarcocystis begins with a carnivore, such as a dog or coyote, consuming muscle from infected intermediate hosts such as bison, moose, elk, sheep, goats, cattle, mule deer, white tailed deer, bighorn sheep, mountain goats, and pronghorn antelope. The parasite develops in the stomach and intestinal tract of the carnivore and produces sporocysts that are passed out in the feces. The sporocysts are resistant to most environmental conditions. The intermediate hosts (bison) become infected when they consume contaminated food or water that contains the sporocysts. In the intermediate host (bison), the sporocysts develop into sarcocysts, which localize in the muscles.
Sarcocystis sporocytes have been found in the muscle of bison in Alberta and Montana (58,59,60,61,62). Bison have been experimentally infected with sarcocystis, by oral inoculation of sporocytes that originated from infected cattle (63). In most cases, intermediate hosts that are infected with sarcocystis do not develop clinical disease.
Clinical signs:
There have been no clinical signs associated with natural sarcocystis infections of bison. Bison calves experimentally infected with large doses of sarcocystis sporocytes became anemic, anorexic, lethargic and had elevated body temperatures (63). It is highly unlikely that bison would be exposed to natural infections as high as those used in this experiment. In Alberta, sarcocystis was found in the muscle of 94% of bison of healthy bison (58). In Montana, sarcocystis was found in the muscle of 13% of healthy bison (61).
Diagnosis:
Diagnosis in the live animal is very difficult. Muscle biopsies can detect the presence of sarcocystis sporocytes in infected bison, but since sarcocystis sporocytes can be found in the muscle of normal bison, their presence does not mean they are the cause of disease.
Treatment:
In cattle, amprolium or salinomycin may reduce clinical signs. There have been no treatment protocols reported for bison. Presently, the risk of bison developing clinical signs associated with sarcocystis is minimal.
Control:
There have been no reasons to develop programs to control sarcocystis in bison.