Potomac horse fever has been confirmed in two Maryland horses, one of which has died from the disease.

The Maryland Department of Agriculture is urging horse owners—especially those with horses that graze near rivers, streams and creeks—to watch their horses closely for signs of the disease. Clinical signs include mild to severe fever, diarrhea, loss of appetite, laminitis, and mild colic. Potomac horse fever is most commonly contracted by horses that ingest infected aquatic insects such as caddisflies and mayflies.

“Potomac horse fever surfaces here every few years,” said State Veterinarian Michael Radebaugh, VMD. “Because it can be fatal, we urge horse owners to pay special attention to how their horses feel. The vaccine for Potomac horse fever is not always effective, so we encourage owners to contact their veterinarian sooner rather than later if they suspect anything, even if the horse has been vaccinated.”

The two horses confirmed were in Frederick County, and both horses had been vaccinated. The second horse is being treated by a private veterinarian and is expected to recover