Four additional cases of Potomac horse fever (PHF) have been confirmed at two veterinary hospitals in Lexington, Ky. Three of the cases were treated at Hagyard-Davidson-McGee (HDM) Veterinary Hospital, where two of the horses are recovering, and one was euthanized. Tests are pending on four other horses at HDM, with their symptoms resembling those found in the clinic’s three confirmed cases. One additional case was seen at Rood and Riddle Equine Hospital.

The first recorded Kentucky fatality from PHF in 2002 was a Thoroughbred filly, which was euthanized June 18 at Rood and Riddle Equine Hospital in Lexington (see https://thehorse.com/ViewArticle.aspx?ID=3702). The cause of the filly’s symptoms was a mystery before the Kentucky Livestock Disease Diagnostic Lab (LDDC) concluded on June 27 that PHF caused the illness.

Bill Bernard, DVM, Dipl. ACVIM, of Rood and Riddle, reported the additional case of PHF diagnosed at that clinic, although the outcome of that case is unknown. Potomac horse fever is normally detected in only one or two horses per year in Kentucky