Potomac horse fever (PHF) is an acute enterocolitis of horses of all ages caused by Neorickettsia risticii. It causes fever, depression, diarrhea and laminitis, and in pregnant mares abortion. It occurs in spring, summer and early fall, mostly on pastures bordering creeks or rivers, and responds to oxytetracycline if treated early.
Key facts
Potomac horse fever (Neorickettsia risticii) at a glance- Species and system: horse; small and large intestine.
- Cause: Neorickettsia risticii, a gram-negative obligate intracellular bacterium with tropism for monocytes.
- Transmission: a trematode vector; likely ingestion of hatched aquatic insects carrying the agent. Sick horses are not contagious.
- Classic presentation: mild depression and anorexia, fever, then diarrhea in about 60% of cases, in a horse on pasture near water in warm months.
- Key complication: laminitis in 20 to 30% of cases.
- Zoonotic: no known zoonotic risk (MSD).
What's inside
13 sections in the full guide- Key facts
- How the NAVLE tests this
- Cause and pathophysiology
- Clinical signs
- Diagnosis
- Differential diagnoses
- Treatment and management
- Working through a case
- Prevention, control and public health
- Prognosis
- Quick review
- Test yourself
- References
The full guide also has 5 tables, 1 figure, 3 self-test questions and 3 references, available to NAVLE members.
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