Factors Associated with Surviving Potomac Horse Fever (AAEP 2012)

While PHF has a serious clinical impact on affected horses, some parameters are associated with survival.
Share
Favorite
Close

No account yet? Register

ADVERTISEMENT

Potomac horse fever (PHF), a somewhat regional rickettsial disease, causes acute diarrhea and leads to death in up to 30% of affected horses. In an effort to understand the disease better, Sandra Taylor, DVM, PhD, Dipl. ACVIM, of Purdue University’s school of veterinary medicine, performed a retrospective study in which she and colleagues looked for specific factors that were favorable for survival among PHF cases. She presented the results at the 2012 American Association of Equine Practitioners’ (AAEP) Convention, held Dec. 1-5 in Anaheim, Calif.

Potomac horse fever is caused by the intracellular bacterium Neorickettsia risticii, which impacts specific white blood cells and cells lining the colon. The disease was first identified in the early 1980s, and while its mode of infection was largely mysterious in the early years, researchers now understand that the reservoir for this bacterium is a fluke, which parasitizes water-borne snails, aquatic insects, birds, and bats. Larval stages of aquatic insects such as mayflies or caddis flies become infected. Birds and bats can eat the aquatic insects and pass the bacteria in their feces. A horse can be exposed by inadvertently ingesting aquatic insects infected with flukes carrying the bacteria (in contaminated forage or feed), or by drinking flukes directly from rivers or streams.

A horse doesn’t require access to rivers or streams to become infected since the flying insects can land anywhere nearby, including in hay or drinking water. Clinical signs begin to appear 12-15 days post-exposure. Vaccines for PHF are mostly ineffective, with an 89% failure rate in preventing disease.

Taylor and her colleagues examined the records of 50 horses diagnosed with PHF over 15 years (1996-2011) and noticed that most cases were seen in August, with some occurring June through December. Blood testing with PCR confirmed positive diagnosis in most horses, while veterinarians found high blood antibody levels against the bacterium in others

Create a free account with TheHorse.com to view this content.

TheHorse.com is home to thousands of free articles about horse health care. In order to access some of our exclusive free content, you must be signed into TheHorse.com.

Start your free account today!

Already have an account?
and continue reading.

Share

Written by:

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

Related Articles

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from TheHorse.com

Sponsored Content

Weekly Poll

sponsored by:

Where do you primarily feed your horse?
328 votes · 328 answers

Readers’ Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form

Create a free account with TheHorse.com!