Sarcocystis

Sarcocystosis

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.
In birds, it is also called "rice breast disease".

Click on the photo to enlarge.

Cysts of Sarcocystis resemble rice grains running parallel to muscle fibres as demonstrated in the breast muscle of a mallard duck.

Distribution

Geographic:

The geographic range of this disease mirrors the range of the species of waterfowl in which it has been reported.

Seasonality:

Infected birds can be found year-round, but is most commonly reported during the waterfowl hunting season.

Hosts, Transmission and Life Cycle

Hosts:

Most commonly observed in dabbling ducks: mallard, northern pintail, northern shoveler, teal, gadwall, American black duck.
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 enter the bloodstream and further infect cells of blood vessels.
The parasite is then carried by the blood to voluntary muscles where the characteristic, elongated cysts are produced. From ingestion of eggs to the formation of cysts takes 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-coloured 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.

Human Health Concerns, Risk Reduction and Edibility of Meat

Sarcocystis presents little health hazard to humans as the parasite is destroyed by cooking. The primary importance to humans of Sarcocystosis in waterfowl is the loss of infected birds for food; 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 Sarcocystosis 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.