PYTHIOSIS: DEADL Y BUT POTENTIALLY DEADLY
Horsekeepers in tropical and subtropical regions are wise to be on the lookout for pythiosis, which is caused by a funguslike organism (Pythium insidiosum) commonly found in swamps and stagnant water.
P. insidiosum usually enters open wounds or other breaks in the skin, but pythiosis can also occur in or near the mouth if the horse grazes infected grass. Characterized by hard, yellow or white coral-like chunks of dead tissue (“kunkers”) that appear in the affected wound, pythiosis also causes swelling around the infection site, as well as the growth of masses of granulomatous tissue, resembling proud0 flesh.
Early diagnosis and treatment are vital for recovery from pythiosis. Surgical removal of infected tissue is the first step, which may be followed by immunotherapy. Research shows that horses treated within 30 days of the occurrence of a pythiosis lesion have a 90 percent or better cure rate. But the recovery rate drops to 50 percent when treatment is initiated 90 days after a lesion develops or later.
Pythiosis is endemic to tropical and subtropical climates. In the United States, most cases occur in the Gulf states: Texas, Louisiana, Mississippi, Alabama and Florida. However, isolated cases have been diagnosed as far north as Wisconsin and New York. The disease can affect any mammal, including people. tools, hay carts, etc.,” says Grenager. “The other challenging factor is that horses can look healthy and still be shedding the pathogen in their manure, especially when they are stressed. This is probably also true of the other animals that periodically shed it---and then it gets into the water supply.”
• S. enterica is divided into six subspecies and more than 2,600 serovars, some of which are normally found in warm-blooded animals and some in cold-blooded animals. But all are zoonotic---meaning that they can cause disease in people as well as animals. In horses, the two most common forms that cause diseases are S. enterica serovar Typhimurium and S. enterica serovar Agona.
“There are thousands of kinds of salmonella and different kinds infect different species of animals,” Grenager says. “Almost any animal can get salmonella, and it can be a serious disease in horses---foals and adults.” Salmonella is common around large livestock operations, and the bacteria can survive in wet environments for months. Many forms of salmonella are becoming resistant to antibiotics.
• Once ingested, salmonella bacteria penetrate the cells in the wall of the intestine and multiply, causing damage that leads to diarrhea. In some cases, the bacteria may get into the bloodstream (septicemia), and infections may develop in other parts of the body. “Foals can become bacteremic or septicemic with infection throughout the body and then localizing in joints and other organs, which can be devastating,” Grenager says.
Salmonellosis generally takes three forms in adult horses:
• A subclinical carrier shows no signs of illness but may shed the bacteria in his manure, which can then