Potomac Horse Fever

As horse owners and lovers, we all know that there are some scary things out there that can make our horses sick. The best way to deal with that is to be as informed and prepared as possible. One of the things that horses in certain areas may deal with is Potomac Horse Fever (PHF), named after the Potomac River where there was a cluster of cases.

In the United States, cases of PHF have been reported mostly in California, Illinois, Indiana, Kentucky, Maryland, Michigan, New York, New Jersey, Ohio, Oregon, Pennsylvania, Texas, and Virginia. It is bacterial, contracted when a horse eats infected snails or insects, as well as drinking water with infected organisms. Horses that become infected are usually grazing near water like creeks or rivers. PHF is seasonal, with most cases occurring in July, August, and September, and it has an incubation period of about 1-3 weeks. Symptoms include:


-Loss of appetite


-Acute laminitis

-Mild colic


-Possible abortion in pregnant mares

There is a vaccine for PHF, but it is not always proven to be effective because there are 14 different strains. Adult horses that have previously been vaccinated for PHF should be re-vaccinated at 6-12 month intervals, sometimes 3 months if you keep your horse in an area where PHF is common. Adult horses that have not been previously vaccinated for PHF should get a booster done 3-4 weeks after the initial vaccination. Foals have a low likelihood of contracting PHF but can still be vaccinated at a certain age.

Although treatable, the mortality rate of PHF is about 5-30% of horses that contract it. Treatments can include IV fluids, laminitis treatment and pain management, and oxytetracycline. Horses will usually respond to treatment within 12-24 hours. Fortunately for us, it’s not transmittable to humans, and infected horses can be housed with susceptible horses because of the way that it is contracted.

There was an outbreak of PHF in Michigan last year very close to where I used to keep my horse. A lot of horses along one stretch of road contracted it, although I’m not sure whether some of those horses were vaccinated or not. None of the horses where I was boarding Moose ended up with it even though there was a small pond in their field. Moose has been vaccinated for PHF ever since I first got him seven years ago and it hasn’t been an issue for us thus far. I try to make a conscious effort not to let him drink out of creeks and rivers to avoid the problem altogether, but on a long trail ride sometimes you just have to let them drink.

This is just a little bit of basic information about PHF so you can stay informed. Always consult your veterinarian about treatment and prevention options!







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