Alarmed about reported cases of Potomac Fever you’ve read about in horses in the St. Louis area?
Three Ozarks vets say not to worry—yet. None have seen recent cases in the Missouri and Arkansas Ozarks. Dr. Michael Spragg, DVM, Spragg Veterinary Clinic near Rogersville, Mo., said his practice saw a case about 10 years ago in the Finley River watershed but none since then, adding that the University of Missouri also diagnosed a case near Republic. While Dr. Pat Badley, DVM, Arkansas state veterinarian with the Arkansas Livestock and Poultry Commission in Little Rock, said he’d seen no cases in Arkansas, “It’s a disease on the way.”
Potomac Fever can be devastating to horses, no doubt about it. It can be fatal if not treated but if diagnosed early is fairly treatable, the vets said.  Symptoms include high fevers in the 105 to 106 degree range, severe diarrhea, depression, lack of appetite, inactivity and weakness, heavy breathing, flared nostrils, even abortion in pregnant mares. Dr. Jeremy Powell, DVM, University of Arkansas Department of Animal Science, said the symptoms resemble those of colic and can lead to laminitis as well.
The disease can be accurately diagnosed through a blood test. Infected horses respond well to doses of oxytetracycline, an antibiotic that can actually activate diarrhea. For that reason, Dr. Spragg tries to let the horse’s immune system do its job and supplement that with tetracycline.
“We want to nudge the body into healing rather than force it into healing,” he said.
The disease takes its name from the Potomac River watershed on the East Coast where it was first detected and recurs frequently. The disease is carried by a microorganism that appears to first infect freshwater snails, aquatic insects and birds found near large bodies of fresh water. Because it is carried by an organism and is not a virus, vaccination against Potomac Fever has not proven to be particularly effective, even in areas where the disease is endemic.
Dr. Powell said the most likely way horses pick up the infection is by eating dead, infected insects in pastures, feedlots or around water tanks.
The vets say there are many far more common diseases and ailments for horse owners to watch for than Potomac Fever. Nevertheless, if your horse has diarrhea, a fever and is off its feed, call your vet immediately. The earlier the diagnosis, the better the prognosis.


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