Kentucky Potomac Horse Fever Update

E.S. Rusty Ford, Equine Operations Consultant for the Kentucky State Veterinarian’s office, provided the following information.

The first confirmed case of Potomac horse fever (PHF) diagnosed in Kentucky during calendar year 2018 was reported on June 1, 2018. Through the week ending August 25, a total of 26 PHF cases have been confirmed. Confirmation of each case was by PCR testing and compatible clinical signs observed. A summary of the cumulative cases is included in the table and graphics below.

Historical Perspective

Kentucky’s PHF cases are first detected later in the year (mid-July), and our thought is the early detection this year was most probably associated with abundant wet weather in April and record-breaking warm temperatures in May.

Horsemen are encouraged to review the environment in which their horses are housed and consult with their veterinarians on strategies they can use to mitigate disease risk. Minimizing opportunity for horses to ingest aquatic insects by turning off lights in and around barns and other areas at night has been suggested.

Potomac horse fever is described to be an acute enterocolitis syndrome that presents as mild colic, fever and diarrhea in horses of all ages. The resulting illness can also cause abortion in pregnant mares. The causative agent, Neorickettsia risticii, is a gram-negative bacterium. Infection of the large intestine results in an acute colitis, which is one of the principal clinical signs of PHF. 

While the disease is often associated with pastures bordering creeks or rivers, it is believed most horses contract PHF after inadvertent ingestion of aquatic insects that carry N risticii and not the water source.