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Sarcocystosis (Rice Breast Disease) |
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| Causative Agent |
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Sarcocystosis is a nonfatal infection, primarily of birds, caused by a
protozoan parasite, Sarcocystis
rileyi.
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This parasite is most
commonly reported in waterfowl, where it is also known as “rice
breast disease”.
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| Images |
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Click on
image to enlarge. |
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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. |
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| Distribution |
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Geographic: |
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The geographic range of this disease mirrors the range of the species of
waterfowl in which it has been reported.
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Seasonality: |
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Infected birds can be found year-round, but the disease is most commonly
reported during the waterfowl hunting season.
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| Hosts, Transmission and Life
Cycle |
| Hosts: |
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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).
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Most
often observed in adult birds.
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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.
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Transmission and Life Cycle: |
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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.
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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.
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The parasite develops in the intestines of the bird,
and then enters the bloodstream, where it further infects
cells of the blood vessels.
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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.
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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.
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| Signs and Symptoms |
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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.
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Cysts
are mostly commonly found within breast muscle of
birds, but can also be seen in heart muscle and muscles of the
limbs.
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Calcium may be deposited around
cysts
which, when cut with a knife, may feel gritty.
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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.
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| Meat Edible? |
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Sarcocystosis
presents little health hazard to humans as the parasite is destroyed
by cooking.
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| Human Health Concerns and
Risk Reduction |
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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.
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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.
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| Samples for Diagnosis |
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The visible presence
of
cysts
within muscle tissue is often sufficient to diagnose this disease.
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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.
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| Further Reading |
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