The name is deceiving, but Potomac horse fever (PHF) is not just a concern for horses near the Potomac River. Cases have been found across most of the United States. Knowing the key signs of PHF and watching carefully for them can help alert owners to protect other horses at risk for infection.

“Every veterinarian and horse owner worries about laminitis and colic. These could be classic signs of PHF in the right context,” says Frank Hurtig, DVM, MBA, Director, Veterinary Services. “Recognizing the signs of disease offers a cue for quick PHF testing, and examination for other disease concerns. Timely vaccination of horses in the area can help prevent against additional cases of PHF.”

Some of the most commonly occurring signs of PHF are:

1. Fever
2. Colic
3. Diarrhea
4. Above signs, followed by laminitis
5. Abortion in pregnant mares

Up to 30% of PHF-infected horses die, and laminitis may continue even after other signs have stopped. If a PHF case is located, all the horses in the area may be at risk for infection, Dr. Hurtig warns.

PHF commonly occurs near bodies of water during mid- to late-summer. However, it has been found in nontraditional areas as remote as northern Wyoming. PHF has a complex life cycle in which Neorickettsia risticii infect freshwater snails containing flukes. Then, N. risticiiis transferred to aquatic insects such as caddisflies and mayflies. Horses become infected after eating grass, feed or water containing these insects.

Draining water and other management practices can help reduce the risk of PHF transmission. To help prevent against the most severe complications of the disease, Dr. Hurtig recommends vaccination.

“Vaccination seems like a simple investment when there is a possibility of colic, laminitis or even death,” Dr. Hurtig says. “In recent years, PHF cases appeared in several nontraditional states. That makes it a real concern for horses in all areas of the country.”

In an efficacy trial, POTOMAVAC™ from Merial protected 86% of horses from clinical disease. POTOMAVAC is proven safe for horses as young as 3 months and is demonstrated safe for pregnant mares. Plus, it is available as Equine POTOMAVAC + IMRAB® to help protect against both PHF and rabies.

Merial is a world-leading, innovation-driven animal health company, providing a comprehensive range of products to enhance the health, well-being and performance of a wide range of animals. Merial employs approximately 5,000 people and operates in more than 150 countries worldwide. Its 2007 sales were nearly $2.5 billion.