By Dr. Frank Hurtig DVM, MBA, director, Veterinary Services, Merial

To protect horses from potentially deadly diseases, owners regularly vaccinate for a variety of common diseases. However, there is a somewhat forgotten foe not always included in every horse’s vaccination regimen.

Traditionally connected to areas surrounding freshwater streams and other bodies of water, Potomac Horse Fever (PHF) has been found in nontraditional areas including northern Wyoming and Minnesota. In fact, PHF is known to occur in 43 states.

“Even though it is commonly tied to Eastern areas, this disease should be a concern for every horse owner — regardless of location,” says Frank Hurtig, DVM, MBA, director, Veterinary Services, Merial. “The most common test for PHF can be inaccurate. That’s why the true geographic range of the disease is not known.”

PHF is traditionally seen in the spring, summer and early fall and is thought to occur when horses ingest aquatic insects, such as caddisflies and mayflies, that carry the disease.

“We associate it as being near waterways, but your farm or ranch doesn’t have to be on a waterway to cause problems with your horse,” says Jonathan Palmer, associate professor of medicine, New Bolton Center, University of Pennsylvania. “It seems to stay in an area even if horses aren’t there or haven’t been there in a while.”

Because PHF boundaries are not certain, it is important to consider your proximity to bodies of water and geographical areas where your horses may travel for competition or other events.

“There are documented instances where horses have gathered at places such as racetracks, where many of the horses have gotten PHF,” says Dr. Palmer.

Horses can be exposed to disease in the stable or during the trip, according to Dr. Hurtig. In fact, any time a horse travels to a new area, there is a chance the horse could contract a disease endemic to that area.

Signs of PHF can include mild depression, anorexia, diarrhea and abortion in pregnant mares. Up to 40% of horses with PHF will develop laminitis.

No matter where you live or where you plan to travel, PHF may be prevented with vaccination. In one study, POTOMAVAC™ from Merial protected 86% of horses from clinical disease. POTOMAVAC is proven safe for horses as young as 3 months. Plus, it is available as a combination of Equine POTOMAVAC + IMRAB® to help protect against both PHF and rabies.