A few cases of Potomac horse fever (PHF) occur each fall in Kentucky. This year, a few cases have been seen, but they occurred a little earlier than normal. Nathan Slovis, DVM, MS, Dipl. ACVIM, of Hagyard Equine Medical Institute, said the early occurrence probably was due to the dry weather the past month.

“It’s nothing new or crazy,” said Slovis. “We usually see cases this time of year (mid-August). We did, however, see cases last month (July), which is earlier than usual.”

Neil M. Williams, DVM, PhD, of the University of Kentucky’s Lexington Disease Diagnostic Center, who did his doctoral studies on PHF, said that at the diagnostic laboratory in Central Kentucky, “We usually have a few cases of PHF each year. For the most part, the number of cases has really fallen off dramatically since the 1980s. This year there have been 13 positive PHF cases, none in May, one in June, 10 in July, and two so far in August. The fact that it is not very commonly seen, and that the signs can vary greatly from case to case, makes it a diagnostic challenge.”

Typically, the first signs of PHF are lethargy, fever, loss of appetite, and possibly diarrhea, said Williams. Any time those signs are encountered, he added, you should seek veterinary assistance. Often what debilitates the horse in a PHF case is laminitis