Potomac Horse Fever Disease Guidelines

Potomac Horse Fever (PHF) is a non-contagious, infectious equine disease caused by the rickettsial organisms Neorickettsia risticii (previously known as Ehrlichia risticii) and Neorickettsia findlayensis. Horses of all ages and breeds residing in endemic areas are susceptible. PHF cases usually occur in summer and fall but may occur in any season depending on weather conditions.

Clinical signs are highly variable, including:

• High fever up to 107° F (41.6^o C) reported. Fevers may occur 7–14 days before signs of colitis develop
• Toxic mucous membranes
• Diarrhea: variable, ranging from absent to severe, which may occur prior to, concurrent with, or after fever
• Anorexia
• Lethargy
• Laminitis (with or without diarrhea)
• Mild to moderate colic
• Altered gastrointestinal motility
• Edema of limbs and ventrum, prepuce of males
• Abortion (by transplacental transmission) 65–111 days post-inoculation