It's that time of the year - Potomac Horse Fever

It’s that time of year again in central Ohio – the prospect of fall is on the horizon, bringing with it crisp, cool weather, a new academic semester, and BuckeyePotomac Horse Fever football, among other things. However, this season also brings with it an increased risk of illness for the horses of Ohio and surrounding states - several diseases have their peak incidence in horse populations during this time of year, particularly those carried by insects. Many are familiar with some important diseases carried by mosquitoes and ticks (think West Nile virus, eastern equine encephalitis, and Lyme disease); however, Potomac Horse Fever, a disease also transmitted by insects, is another serious threat to the health of Ohio’s horses and is often overlooked until it is too late.

Potomac Horse Fever (PHF), caused by infection with a bacterium called Neorickettsia risticii, is transmitted to horses through aquatic insects (such as caddis flies and mayflies) and has its peak incidence in the months of July, August, and September. These insects, which reproduce in creeks and streams, are thought to be consumed by horses when they die on pasture or other feed sources, thereby transmitting the infection. Even though the disease is infectious, it is not considered directly contagious from one horse to another; horses living on the same property do share the same risk of exposure to infected insects, and the disease can be a farm problem year after year. PHF most commonly causes diarrhea in adult horses, but infected horses can display any combination of fever, inappetance, colic, diarrhea, and laminitis. Therefore, it is important to be vigilant for any of these signs in horses in endemic areas during the disease season and to initiate treatment as soon as possible.

If a horse is showing signs consistent with PHF during the peak season, a veterinarian can run tests to definitively diagnose the condition. Even though treatment is often started before the results of these tests are complete, running them is still worth the extra effort and expense - having a confirmed diagnosis of PHF on a farm should encourage monitoring of other horses on the property for any evidence of infection, as early detection may save horses’ lives. Taking body temperatures at least once (preferably twice) daily may be the best way to detect early PHF; any horses with fevers (> 102 degrees F) should receive veterinary evaluation as soon as possible.