Pythiosis: A danger in the water

I lost my beloved mare to pythiosis and hope to increase awareness of this devastating disease so fewer horses will share her fate.
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Belle was my dream horse. I’d raised her from birth, and she was one of the prettiest Appaloosas I ever saw. She was intelligent. Sometimes I think she read my mind, and she could give me a look that was almost human.

Sadly, I lost Belle in May 2015 after a 10-month battle with a horrible infection I’d never heard of---pythiosis.

In spring of 2014 we had abundant rain here in Georgia. Part of our property flooded, and a few weeks later the pond was full of grasses and lily pads. My horses had access to this pond for 25 years. They would stand in the water to escape flies and occasionally roll in it. In July 2014, I found two tiny cuts on Belle’s forearm and belly. Within days, they had grown, and they looked like summer sores---infections that occur when flies deposit stomach worm larvae in open wounds.

My veterinarian dewormed Belle and treated the lesions with an antibiotic ointment. But two weeks later, the sores were six inches in diameter. A biopsy confirmed pythiosis. Immediately I searched online for information. My heart sank when I saw case photos. This was going to be a long fight.

Pythiosis occurs when a fungus-like organism (Pythium insidiosum) enters a wound. The organism is found in still or stagnant water, and most animals pick it up while wading, but it can also enter wounds near the mouth as a horse grazes wet grass. One hallmark of pythiosis is the appearance of coral-like chunks of hard material, called “kunkers,” within the wound. Because P. insidiosum isn’t a true fungus, it does not respond to antifungal or other antimicrobial medications. The primary treatment is surgical removal the infected tissue, followed by immunotherapy shots.

Throughout the fall and winter, Belle battled this nasty disease. She seemed to respond to first round of immunotherapy shots, but after the second round the lesions grew larger and bloodier. Belle’s itching was relentless. Finally, I had no choice but to end my beautiful mare’s suffering.

Pythiosis is not a reportable disease, so there’s no way to know how many cases occur each year. However, through social media I found 15 equine cases diagnosed in Georgia in 2014 and 2015. And I’ve learned that in 2015, more than 1,000 serum shots were shipped to Georgia for horses and dogs.

The disease is typically found in tropical and subtropical climates, and in the United States it has been seen primarily in the states bordering the Gulf of Mexico. However, isolated cases have occurred farther north. With warming climates, I wouldn’t be surprised if the normal range of this disease begins to spread northward.

And that could mean serious trouble for horses, dogs and other mammals, including people. Starting treatment early is critical: Research has shown the survival rate may be 90 percent or higher among horses treated for pythiosis within the first 30 days of infection, but the rate drops to less than 50 percent when treatment isn’t started for 90 days after infection. The challenge with pythiosis is that it can look like other common problems at first. Many veterinarians do not consider it as a possibility right away.

If your horse develops a bloody sore that continues to grow despite treatment, ask your veterinarian to test for pythiosis. I’d also suggest that you reconsider whether to allow you horse access to ponds and other wet areas.

If I can take any solace from losing Belle, I hope it will be from helping save other horses from this dreadful disease.

This article first appeared in the July 2017 issue of EQUUS (Volume #378)