Potomac Horse Fever in Horses: Causes, Symptoms, Treatment & Prevention
Late summer, freshwater edges, big fevers, bad diarrhea—and a laminitis risk you can’t ignore. Here’s the rider-first plan to spot PHF early, act fast with your vet, and prevent the next case.
What PHF Is & How It Spreads
Potomac Horse Fever (PHF) is an acute enterocolitis caused by Neorickettsia risticii. Horses are infected when they ingest aquatic insects (e.g., mayflies, caddisflies) or snails that carry the organism. Risk increases for barns near freshwater streams, ponds, canals, or irrigation ditches, especially in late summer and during hatch events that concentrate insects around lights and waterers.
Clinical Signs & Complications
- High fever and profuse watery diarrhea
- Mild colic, lethargy, inappetence, dehydration, electrolyte loss
- Laminitis (major complication—treat as an emergency)
- In pregnant mares: abortion
- Endotoxemia signs in severe cases
Immediate Action Call your veterinarian at the first combination of fever + diarrhea in late summer—fast therapy changes outcomes.
Diagnosis & Treatment
How Vets Confirm PHF
- PCR on whole blood and/or feces
- Serology: acute/convalescent titers to support diagnosis
- Season, location, and water/insect exposure history matter
Treatment Priorities
- Antibiotics promptly (commonly oxytetracycline under veterinary supervision)
- Aggressive fluids & electrolytes to correct dehydration and losses
- Anti-inflammatories/anti-endotoxin strategies as directed
- Laminitis prevention—ice feet, deep bedding, frequent checks
- Quiet housing; monitor temperature, manure, hydration, feet
Timeline Many horses improve within 24–48 hours of appropriate antibiotic therapy—don’t delay the call.
Prevention: Vaccines, Water & Insects
Vaccination
- Used in endemic regions; may reduce severity but isn’t fail-safe across strains
- Boost before peak insect season per your veterinarian
Water-Source Management
- Limit horse access to ditches, canals, and stream edges
- Reduce standing water; adjust lighting to avoid attracting mayflies near stalls/waterers
- Clean waterers frequently; shield or relocate lights
Insect Control & Hygiene
- Daily manure removal; tidy feed areas and bins
- Layered repellent plan: Citraquin® 32oz and the Citraquin® collection—see the How-To Guide
- Wash down walls, doors, and trailers with SuperClean™ Stall & Trailer Cleaner
Product Synergy (Real-World Use)
Hydration & Comfort
Hydro-Lyte® — sugar-free electrolytes to support rehydration plans without adding carbohydrates.
MasterMudd™ EquiBrace — massage-in support rub riders use for muscle comfort during recovery. (CryoSpray may be used similarly where applicable.)
Skin/Environment Support
- Rapid Relief Restorative Cream — thin, water-resistant barrier for intact, healed skin around rub-prone zones.
- For wound/skin questions your vet approves, consider RESTOREaHORSE® Liqui-Gel as part of a gentle cleansing routine (per veterinary direction).
- SuperClean™ — keep high-touch zones sanitary during episodes.
These products don’t treat PHF; they support hydration, comfort, skin, and hygiene alongside your veterinarian’s medical plan.
PHF — FAQ
How fast can PHF progress?
Fever and diarrhea can escalate within hours. Early antibiotics and fluids are critical; laminitis can develop quickly without proactive prevention.
Should I isolate a PHF horse?
PHF isn’t typically horse-to-horse contagious, but good biosecurity (separate tools, clean buckets, disinfect surfaces) is smart during any diarrheal disease episode.
When can I return to work?
Only after your veterinarian clears the horse. Rebuild gradually with attention to hydration, manure quality, and hoof comfort.
Educational note: This article provides general information and is not a substitute for veterinary diagnosis or treatment. Always follow your veterinarian’s guidance for testing, antibiotics, fluids/electrolytes, and laminitis prevention.
