Potomac Horse Fever in Donkeys: Fever, Diarrhea, and Seasonal Risk
- Potomac horse fever is an equine bacterial disease linked to *Neorickettsia risticii* and can affect donkeys as well as horses.
- Common signs include fever, depression, reduced appetite, diarrhea, and a risk of laminitis. Diarrhea may be mild, delayed, or sometimes absent early on.
- Risk is highest in warmer months, especially from late spring through fall, and in animals living near streams, ponds, irrigation ditches, or other freshwater habitats with aquatic insects.
- This is not considered a horse-to-horse or donkey-to-donkey contagious disease. Infection is associated with accidental ingestion of infected aquatic insects.
- See your vet promptly if your donkey has fever, diarrhea, dullness, or sore feet. Early treatment can improve the outlook.
What Is Potomac Horse Fever in Donkeys?
Potomac horse fever is an infectious disease of equids caused by Neorickettsia risticii. It is best described in horses, but donkeys are also equids and may be affected. The illness often causes fever, depression, reduced appetite, and diarrhea, and some animals develop laminitis, which can become the most serious complication.
Despite the name, this disease is not limited to the Potomac region. Cases have been reported across many parts of the United States, especially where freshwater insects are common. The disease is seasonal, with most cases occurring in warmer months when aquatic insects hatch and are more likely to be eaten accidentally.
For pet parents, the key point is that Potomac horse fever can start with vague signs before diarrhea becomes obvious. A donkey that seems quiet, warm, off feed, or uncomfortable may need prompt veterinary attention even before the manure changes. Early recognition matters because supportive care and timely antibiotics may reduce complications.
Symptoms of Potomac Horse Fever in Donkeys
- Fever, often one of the earliest signs
- Depression, dull attitude, or reduced interest in feed
- Diarrhea, ranging from soft manure to severe watery diarrhea
- Mild colic signs such as pawing, looking at the flank, or restlessness
- Dehydration or tacky gums from fluid loss
- Laminitis signs, including heat in the feet, reluctance to move, or shifting weight
- Increased heart rate or weakness in more serious cases
Potomac horse fever can look different from one donkey to another. Some develop a high fever first and diarrhea later, while others show only vague signs early on. Diarrhea can be absent at the beginning, so a quiet donkey with fever and poor appetite still deserves attention.
See your vet immediately if your donkey has fever plus diarrhea, seems dehydrated, will not eat, or shows any signs of sore feet or laminitis. Laminitis can develop quickly and may have long-term effects even if the intestinal signs improve.
What Causes Potomac Horse Fever in Donkeys?
Potomac horse fever is caused by Neorickettsia risticii, a bacterium with a complex life cycle linked to freshwater snails, flukes, and aquatic insects. Equids are thought to become infected when they accidentally eat infected insects such as mayflies, caddisflies, damselflies, or similar aquatic insects that land in feed, water, or pasture.
This helps explain the seasonal pattern. Risk tends to rise from late spring through fall, with many cases reported from May through October and peaks often occurring in summer or early fall. Donkeys living near creeks, ponds, rivers, irrigated pasture, or flood-prone areas may have greater exposure.
The disease is considered non-contagious between equids under normal conditions. In other words, your donkey is not thought to catch it directly from another donkey. Instead, the main concern is shared environmental exposure to infected aquatic insects.
How Is Potomac Horse Fever in Donkeys Diagnosed?
Your vet will usually start with the history, season, environment, and physical exam findings. Fever, diarrhea, depression, and laminitis risk during warm months near freshwater can raise suspicion, but these signs are not unique to Potomac horse fever. Other causes of colitis, fever, and foot pain may need to be considered.
Definitive diagnosis is typically based on identifying Neorickettsia risticii with PCR testing on blood or feces. In some cases, paired antibody testing may add context, but PCR is especially useful in active disease. Your vet may also recommend bloodwork to assess hydration, inflammation, protein loss, and organ function, along with hoof evaluation if laminitis is a concern.
Because donkeys can mask illness, diagnosis may depend on noticing subtle changes early. If your donkey seems quieter than normal during insect season, prompt testing and supportive care discussions with your vet are reasonable.
Treatment Options for Potomac Horse Fever in Donkeys
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm call or exam with basic assessment
- Targeted bloodwork as needed
- Empiric treatment plan guided by your vet when PHF is strongly suspected
- Oral or limited injectable medications when appropriate
- Basic fluid support if dehydration is mild
- Early laminitis monitoring, stall or dry-lot rest, and hoof support discussions
Recommended Standard Treatment
- Exam and fuller diagnostic workup, often including CBC, chemistry, and PCR testing on blood or feces
- Tetracycline-class antibiotic treatment selected by your vet, commonly oxytetracycline in equine cases
- IV or enteral fluids based on dehydration level
- Anti-inflammatory and pain-control plan tailored to GI and hoof risk
- Laminitis prevention and monitoring, including digital pulse checks and hoof support
- Short-term hospitalization or repeated on-farm reassessments when needed
Advanced / Critical Care
- Referral hospital care or intensive field management
- Continuous or repeated IV fluid therapy and electrolyte support
- Frequent bloodwork and advanced monitoring for protein loss, kidney values, and systemic inflammation
- Aggressive laminitis prevention or treatment with farrier and hoof-support involvement
- Nasogastric support, plasma or colloid support when indicated, and management of severe colitis complications
- 24-hour nursing care for weak, recumbent, or rapidly worsening patients
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Potomac Horse Fever in Donkeys
Bring these questions to your vet appointment to get the most out of your visit.
- You can ask your vet whether my donkey's signs fit Potomac horse fever or another cause of fever and diarrhea.
- You can ask your vet which tests are most useful right now, including whether PCR on blood or feces makes sense.
- You can ask your vet how worried we should be about laminitis and what early hoof-support steps may help.
- You can ask your vet which treatment tier fits my donkey's condition, goals, and budget.
- You can ask your vet whether hospital care is recommended or if safe treatment at home is realistic.
- You can ask your vet how quickly we should expect fever or manure changes to improve after treatment starts.
- You can ask your vet what dehydration signs, foot pain signs, or manure changes mean I should call again right away.
- You can ask your vet whether vaccination is appropriate for my donkey based on our region, water exposure, and seasonal risk.
How to Prevent Potomac Horse Fever in Donkeys
Prevention focuses on reducing exposure to infected aquatic insects and discussing vaccination with your vet when risk is meaningful. Donkeys kept near ponds, streams, rivers, irrigation canals, or wet pasture may have more exposure during insect season. Turning off barn lights at night, especially during heavy insect hatches, may help because aquatic insects are attracted to light and can end up in feed and water.
Good management can also help. Clean water sources regularly, avoid letting feed sit where insects collect, and pay extra attention after mayfly or caddisfly swarms. If possible, reduce grazing or feeding in areas where dead insects accumulate around lights, troughs, or water edges.
Vaccination is available for Potomac horse fever in horses and is often timed before peak summer risk in endemic areas. However, protection is not complete, and vaccinated equids may still become ill, though disease severity may be reduced. Because data specific to donkeys are limited, the best plan is an individualized conversation with your vet about local risk, timing, and whether vaccination fits your donkey's situation.
Even with prevention, early recognition remains important. During warm months, monitor your donkey closely for fever, dullness, appetite changes, loose manure, or sore feet so your vet can step in quickly if needed.