(NC) Potomac Horse Fever was presumptively diagnosed by a positive serum titer of 6400 by indirect fluorescent antibody (IFA). The sample was collected from a clinical animal on 4/30/2018 and reported by the laboratory on 5/4/2018. The horse presented with diarrhea, fever, and laminitis. Blood chemistry revealed hypoproteinemia, hyperbilirubinemia, increased creatinine, BUN, and electrolyte abnormalities.

EDTA whole blood for PHF PCR is the preferred sample of choice for acute infections, but both EDTA whole blood and serum may assist in the diagnosis if the animal is seen later in the course of the illness or animal recovers without an initial diagnosis. Ancillary testing for equine beta corona, fecal parasites, Salmonella, Clostridial toxins and enterotoxins were negative. There was no history of PHF vaccination.

Per the referring veterinarian, the weather had been unseasonably warm at the time of presentation. Unusually warm weather may cause aquatic insect hatches earlier than typically seen at that time of year; therefore, PHF should be on the differential diagnosis for horses with signs compatible with a diagnosis of PHF. Oxytetracycline was administered along with supportive care. At the time of contact with the referring veterinarian, the animal was alive.