Potomac Horse Fever Cases Reported in New York; Vets Encourage Vaccination

Officials have confirmed the number of Potomac Horse fever (PHF) cases in northern New York has been higher than usual in recent weeks, encouraging owners to vaccinate but noting that a rise in cases is relatively common this time of year.

An article printed in the Aug. 14 edition of the Watertown Daily Times reported there is an "outbreak" of the "life-threatening gastrointestinal disease" Potomac horse fever.

Potomac horse fever (PHF), or equine monocytic ehrlichiosis, is caused by the bacterium Neorickettsia risticii. Clinical signs include fever, mild to severe diarrhea (although some cases have no evidence of diarrhea), laminitis, mild colic, and decreased abdominal sounds. In rare instances affected pregnant mares abort. The disease is treatable if caught in the early stages, but it can be fatal. N. risticii has been has been linked to parasites of freshwater snails that also infect the larvae of mayflies and caddis flies in fresh water. When the infected fly larvae mature into infected adult flies, they can be ingested by horses inadvertently.
According to Jessica Chittenden Ziehm, director of Communications at New York State's Department of Agriculture & Markets, "Potomac horse fever is not uncommon at this time of year, especially in northern New York State, so it would be difficult to classify this as an outbreak at this time."

Cornell University veterinarians concur with Ziehm.

"We are dealing with an increased number of cases at present," said Linda Mittel, MSPH, DVM, senior extension associate at Cornell University's Animal Health Diagnostic Center. "We usually do see an increase in PHF in late August and early September and it appears that due to the increased heat and insect activity we are seeing the annual surge in cases a little earlier this year."

Still, Mittel and colleagues are not convinced at this time that they are dealing with an outbreak, as the number of horses diagnosed with PHF is not yet high enough.

Both Mittel and Ziehm are encouraging owners to consider the PHF vaccine.

"There is some data suggesting the vaccine has questionable efficacy, but it is the best option for protecting horses in New York state (and other at-risk horses) against PHF at this time," Mittel noted.

More information on PHF:

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.