Pythiosis in Horses

September 28, 2009 (published)

Today on the program I am going to talk about an uncommon skin infection in horses called pythiosis, or phycomycosis, that does occur in Texas.  Dr. Susan White from the University of Georgia indicates these are not true fungi but are actually plant pathogens that cause disease in horses.  Most of the time, this occurs when horses have small cuts or scrapes on the skin and they become infected standing in stagnant water or wet grass.  The disease is most commonly found in the Gulf Coast states and most lesions are on the horse’s legs or under the belly. 

After infection, the lesions quickly enlarge and drain pus and bloody fluid. They are nasty lesions.  Because they can look like other infections, it is important for your vet to take a piece of the tissue to get an accurate diagnosis.  One unusual characteristic is these lesions contain little hard calcified masses called kunkers.  Unfortunately, these cases are difficult and some horses have to be euthanized if the lesions are too advanced to treat.  If the lesions are found early, they can be removed surgically but many times the lesion will recur.  Antifungal medications are not effective since these organisms are not true fungi.  There is a vaccine produced by Pan American Veterinary Labs in Hutto, Texas, that has shown good success in early cases of pythiosis and even some response in chronic cases. If your horse has a rapidly growing skin lesion that is not responding to normal wound treatment, contact your vet as soon as possible because early cases of pythiosis have a much better prognosis than ongoing cases.

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