Beware: That Summer Sore Could Be Pythium


I got a call from a friend of mine a while back. Pam LiVecchi owns Desert Rose Ranch in Jupiter, and she was concerned. A boarder’s horse had gotten what looked like a summer sore, but it had rapidly progressed to something much more insidious and horrible.

“I never heard of this disease before, but apparently it’s rampant in South Florida,” LiVecchi said. “It has killed a lot of horses around the state over the years. Most people see a summer sore and don’t worry, but they should get their horse tested immediately and be ready to act swiftly before it progresses.”

Pythium insidiosum is also called swamp cancer and Florida leeches, even though it’s a fungal disease. Sixty percent of the recorded cases are found in — you guessed it — South Florida. It thrives in wet, swampy areas.

I’d had a friend who battled it a couple of years ago. Happily, her horse survived. It had started in her horse’s hooves.

The coronet bands were mushy, and there was an awful discharge from the frogs, an amber, gel-like substance that oozed out near the heel and smelled awful. The heels turned yellow, then peeled off.

At the time, I visited Palm Beach Equine and spoke with veterinarians Scott Swerdlin and Bob Brusie, who’ve both seen more cases of pythium than they’d like.

“The name sounds horrible, and the disease is even worse,” Swerdlin said.

“This invasive fungus invades healthy tissue through a break in the skin anywhere, though the forelimbs are more susceptible,” Brusie added. “It can take over a summer sore. The smell of it drives you out of the room. The discharge is a mixture of pus, slime and mucous. Bandages get rapidly saturated.”

Pythium lesions expand exponentially. “It seems to be very itchy, as horses typically chew at the lesions, excoriating and savaging them with their teeth,” Brusie continued. “And yes, it can be fatal in spite of treatment. A horse can go down in 10 days.”

The only way to definitively diagnose it is through a blood test.”

“There is a vaccine which won’t prevent the disease, but is only given if the horse has pythium,” Swerdlin said. “That’s not enough, however. The affected tissue must be surgically removed, or the disease will keep on growing. You have to treat it like a cancer and cut it all out. If it reaches the bone or a joint, then it’s all over.”

The problem, of course, is that it almost always first presents as a common summer sore.

“People are used to seeing and treating summer sores, so they doctor them themselves,” Swerdlin said. “But if a week passes and nothing gets better or things get a lot worse, that’s valuable time lost.”

Oddly enough, pythium and summer sores were very rare down here from 1985 through 2008. “That was due to the efficacy of the main dewormer people used,” Brusie said. “Horse owners were very good at keeping their horses on a deworming schedule.”

“But it’s not as effective as it used to be,” Swerdlin added. “So now we need different methods. The main way to avoid trouble is through parasite control, including flies who breed in the water of manure bins. Ideally, manure should be removed weekly, breaking the 10-day fly reproduction cycle. Also, don’t turn horses out where there’s swampy, stagnant water. Standing in muck or boggy areas is just begging for trouble. Keep all wounds covered, and clean stalls and pastures on a regular basis.”

Brusie said that people should drain all the swampy areas on their property.

“Or at least make sure they’re off-limits to the horses,” he said. “This disease is not spread horse-to-horse, but in rare cases, people can contract it through close contact with an infected site, so they should use gloves when treating the lesions.”

After the vets, I called Bob Glass, owner of Pan American Veterinary Labs, in Hutto, Texas. He was friendly and extremely knowledgeable, having investigated pythium for years.

“I’ve probably seen and known about more cases than most people,” he said. “I developed the blood test and vaccine, along with Dr. [Leonel] Mendoza. There are some real hot spots for this disease, especially South Florida… It tends to crop up from April through December.”

When the asexual plant reproduces, it sends out zoospores in the water. “If they find an animal before they find another plant, they’ll stay there,” Glass said. “We’ve found pythium in horses, dogs, cats, people, llamas, camels, bears, dolphins and grasshoppers. In horses, 90 percent of the infections are on the skin, even healthy unblemished skin, though they can attack hooves and even the throat, if they’re ingested, either through drinking water or from infected grass. This will present as a dry cough or roaring.”

The only way to prevent pythium is through vigilance, he said.

“Check each horse every day, and don’t wait if you see a persistent sore or one that gets rapidly worse,” Glass said. “If treatment is given within the first 30 days, there’s a 95 percent success rate. That falls to 75 percent within the first 90 days, and beyond that, 50 percent or less.”

For more information, visit the Pan American Veterinary Labs web site at