Sarcosporidiosis
Sarcocystis or rice breast disease is a
nonfatal, usually asymptomatic infection that is caused by a
parasitic protozoan. Various species of this parasite affect
mammals, reptiles and birds. The most commonly reported species
of the parasite in North America is Sarcocystis rileyi, the
species most commonly found in waterfowl.
Birds ingest the eggs or oocyst of the mature parasite in food
or water that
is contaminated by carnivore feces, which contain the oocysts.
The oocysts
develop in the intestine of the bird into an intermediate form,
the sporozoites, that enter the bird's bloodstream and infect
specific cells of the blood vessels. Multiplication of these
cells gives rise to a second intermediate form, merozoites, that
are carried by the blood to the voluntary muscles, where
elongated cysts or macrocysts are eventually
produced. The life cycle is completed when a carnivore ingests
the infected
muscle tissue of a bird and the parasite reaches maturity and
releases
oocysts in the intestines of the carnivore.
Sarcoystis is a common parasitic infection of some waterfowl
species, and it is found throughout the geographic range of
those species in North America. Usually, there is no externally
visible sign of this disease nor is it recognized as a direct
cause of migratory bird mortality. Severe infections can cause
loss of muscle tissue and result in lameness, weakness, and even
paralysis in rare cases. The debilitating effects of severe
infections
could increase bird susceptibility to predation and to other
causes of
mortality.
Visible forms of infection are readily apparent when the skin is
removed from the bird. In waterfowl and in many other species,
infection appears as cream‑colored, cylindrical cysts (the
macrocysts) that resemble grains of rice running in parallel
streaks through the muscle tissue. The cysts are commonly found
in the breast muscle, but they are also found in other skeletal
and cardiac muscle.
There are no known control methods for this disease, nor do any
seem to be needed or are any being developed as current
knowledge of the disease does not indicate any evidence that
bird health is often compromised by infection. Nevertheless, the
role of carnivores in the life cycle of Sarcocystis sp.
infections should be considered when feeding uncooked, infected
waterfowl to house pets and to farm animals such as hogs.
Sarcocystis sp. presents no known health hazard to humans. The
primary importance to humans of sarcocystis in waterfowl is the
loss of infected birds for food; the unaesthetic appearance of
parasitized muscle may prompt hunters to discard the carcass.