Potomac Horse Fever (PHF) is a non-contagious, infectious equine disease caused by the rickettsial organism Neorickettsia risticii (previously known as Ehrlichia risticii). The disease can affect any age, breed or sex of horse. PHF cases usually occur in summer and fall, but may occur in any season depending on weather conditions.
Risk factors for PHF include housing near (within approximately 5 miles) a freshwater stream or river or on irrigated pasture in endemic areas; and nighttime use of barn lights which attract parasitized insects.
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