Potomac Horse Fever, or PHP, primarily affects horses living near a river such as the Potomac, which runs through parts of Virginia and Maryland. This disease is caused by a rickettsial parasite called Ehrlichia risticii, which is transmitted by an unknown arthropod vector in areas along rivers throughout North America. Clinical signs of infection are most commonly seen during the summer months.
Gastrointestinal problems such as diarrhea will accompany a PHF infection. Frequently, horses will develop laminitis several days after the diarrhea starts. Treatment is essential for correcting and preventing severe dehydration, which can cause death. Severely affected animals often are euthanized due to the poor quality of their lives.
Vaccinations can help reduce the severity of the clinical signs, but usually will not prevent the disease in an outbreak. With appropriate veterinary care, however, most horses can be treated successfully.
