In areas where the disease
is commonly observed, pythiosis occurs primarily during the summer months,
especially after periods of high precipitation. It has been noted that
horses allowed to graze for a period of time in stagnant water frequently
develop pythiosis. However, cases of pythiosis in equines, dogs, and
humans never exposed to stagnant water, indicate that the infection
can also be acquired after contact with soil and grass containing P.
insidiosum.
Due to its occurrence in wet environments and summer months the disease
has been termed: swamp cancer, Florida horse leeches, summer sores,
burusattee (“rain” in India).
Pythium insidiosum has been reported more frequently in tropical and
subtropical regions of the world. However, cases in temperate areas
of Japan and USA indicate that this organism can be found in cooler
environments as well. Well documented cases of the disease have been
reported in Australia, the Pacific islands, Asia, and the Americas.
It would seem that the tropical climate of much of Africa would make
it suitable for P. insidiosum. However, so far, no cases of pythiosis
from that continent have been reported.
In the Americas, the disease is known to occur in North, Central and
South America as well as the Caribbean islands. In the United States,
the disease is more commonly reported in the states along the Gulf of
Mexico: Alabama, Florida, Louisiana, Mississippi, and Texas. However,
several cases in dogs, equines and humans have occurred in states such
as Georgia, Illinois, Missouri, North, Oklahoma, and South Carolina,
Tennessee (human), New Jersey, New York, and Wisconsin.
Cases in Central America have also been reported in Guatemala, Nicaragua,
Costa Rica, and Panama. In South America, Argentina, Colombia, Venezuela,
and Brazil have reported the disease.
LIFE CYCLE: Pythium insidiosum, like other Pythium
spp, need wet environments to carry out their life cycle in nature although
it can survive in wet soil with grass because of its ability to produce
resistant spores. Several investigators have shown that this pathogen
requires some plants to complete its life cycle in nature (lily and
gramineae (grass). It is believed that the zoospores are the infecting
units. Zoospores in water will become attached to the tissue in breaks
in the host's skin, intestinal tract and other sites. The zoospores
will encyst and then produced hyphae that will, mechanically penetrate
the tissue and cause the disease. The majority of cases in equines occur
through open wounds on the skin of the extremities and areas in contact
with water or grass. In Dogs, the disease is observed in the skin and
the intestinal tract. This is due to the fact that dogs may drink water
and/or eat grass contaminated with P. insidiosum.
6/16/04
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