Threats thewater in POTOMAC HORSE FEVER

Summer is the peak season for a number of diseases caused by organisms that thrive in ponds, streams and marshes. Here’s how you can protect your horse.

Horses contract Potomac horse fever (PHF) by ingesting the bacterium Neorickettsia risticii, which may be present in a number of species that inhabit ponds, rivers and other natural waterways. “We know that a big risk factor is proximity to a water source or river---usually within five miles, but that isn’t always the case,” says Michelle Abraham Linton, BSc, BVMS, DACVIM (LAIM), of the University of Pennsylvania at New Bolton Center. PHF tends to be seasonal, occurring mainly in the hot summer months when aquatic species are most active.

The disease was named after the Potomac River Valley, where it was first recognized in 1979, but it can occur practically anywhere under the right conditions. “If we look at blood tests on horses all across the United States, many of them show evidence that they’ve been exposed,” Linton says. “Incidence and severity varies, possibly because some horses are more susceptible, and it may also depend on how much they ingest.”