Epidemiology of Pythium insidiosum
In areas where the disease is commonly observed, pythiosis occurs during the summer months especially after periods of high pluvial precipitation. It was noted that horses that had grazed for a period of time in stagnant water frequently developed pythiosis. However, cases of pythiosis in equines, dogs, and humans never exposed to stagnant water, indicated that the infection can also be acquired after contact with soil and grass containing resting structures of P. insidiosum (perhaps oogonia).
Due to its occurrence in wet environments and summer months the disease has been termed: swamp cancer, Florida horse leeches, summer sores, burusattee (means rain in India), espundia, granular dermatitis and others.
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. But so far only one case of dog pythiosis in Bamako, Mali has been recorded (Emerg. Infect. Dis. 11:479;2005).
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 as far north as Wisconsin.
Cases in Central America have also been reported in Guatemala, Nicaragua, Costa Rica, and Panama. In South America, Argentina, Colombia, Venezuela, and Brazil had also reported the disease.