Sarcocystosis (Rice Breast Disease) Cook Thoroughly Do Not Feed To Pets
Causative Agent
  • Sarcocystosis is a nonfatal infection, primarily of birds, caused by a protozoan parasite, Sarcocystis rileyi.
  • This parasite is most commonly reported in waterfowl, where it is also known as “rice breast disease”.
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Cysts of Sarcocystis resemble rice grains running parallel to muscle fibres, as demonstrated in the breast muscle of a mallard duck.
  • The geographic range of this disease mirrors the range of the species of waterfowl in which it has been reported.
  • Infected birds can be found year-round, but the disease is most commonly reported during the waterfowl hunting season.
Hosts, Transmission and Life Cycle
  • Most commonly observed in dabbling ducks: mallard (Anas platyrhynchos), northern pintail (A. acuta), northern shoveler (A. clypeata), teal (A. crecca, A. discors), gadwall (A. strepera), and American black duck (A. rubripes).
  • Most often observed in adult birds.
  • A large number of species of Sarcocystis also occur in domestic and wild mammals. In most mammals the disease is only found microscopically; however, livestock and even humans have been affected with severe infections.
Transmission and Life Cycle:
  • The life cycle of Sarcocystis requires two hosts: an intermediate host (waterfowl) for the asexual component and a definitive host (mammalian carnivore) for the sexual stage.
  • Birds ingest water contaminated with the feces of carnivores that contain the eggs of Sarcocystis. Eggs may persist in the environment for extended periods of time.
  • The parasite develops in the intestines of the bird, and then enters the bloodstream, where it further infects cells of the blood vessels.
  • The parasite is then carried by the blood to voluntary muscles where the characteristic, elongated cysts are produced. The time it takes from ingestion of eggs to the formation of cysts is several months.
  • When a carnivore ingests infected muscle tissue from a bird, the life-cycle is completed. The parasite reaches maturity in the intestines of the carnivore and repeats the cycle by producing eggs.
Signs and Symptoms
  • Cream-colored cylindrical cysts (several mm long), resembling rice grains, that run in parallel streaks within muscles characterize this disease when the infection is visible to the naked eye.
  • Cysts are mostly commonly found within breast muscle of birds, but can also be seen in heart muscle and muscles of the limbs.
  • Calcium may be deposited around cysts which, when cut with a knife, may feel gritty.
  • Severe infections can result in loss of muscle tissue and result in lameness, weakness and even paralysis; debilitation could increase susceptibility to predation and other causes of mortality.
Meat Edible?
  • Sarcocystosis presents little health hazard to humans as the parasite is destroyed by cooking.
Human Health Concerns and Risk Reduction
  • The primary importance to humans of Sarcocystis in waterfowl is the loss of infected birds for food as the unaesthetic appearance of parasitized muscle may prompt hunters to discard the carcass.
  • However, at this time, some scientists feel that so much is unknown about infections of Sarcocystis that it is recommended that infected meat from ducks and rabbits not be used for human consumption or fed to cats and dogs.
Samples for Diagnosis
  • The visible presence of cysts within muscle tissue is often sufficient to diagnose this disease.
  • Whole birds should be submitted; however, frozen samples of muscle tissue or muscle tissue preserved in a 10% formalin solution may be submitted for diagnosis.
Further Reading
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