Equine Herpesvirus Myeloencephalopathy in Donkeys: EHV-1 Neurologic Disease Explained

Equine herpesvirus myeloencephalopathy, often shortened to EHM, is the neurologic form of infection with equine herpesvirus-1 (EHV-1). The virus is well known in horses, but donkeys are also equids and can become infected. In neurologic cases, the main problem is damage to blood vessels that supply the spinal cord and brain, which can lead to weakness, poor coordination, bladder problems, and sometimes sudden worsening.

EHV-1 is common in equine populations because infected animals can carry the virus in a latent form for long periods and then begin shedding again during stress, illness, transport, crowding, or other immune challenges. That means a donkey may be exposed by a horse, mule, or donkey that does not look obviously sick at the time.

For pet parents, the most important point is that neurologic signs are an emergency. Some donkeys stay standing and recover with supportive care, while others decline over hours to a few days. Early veterinary involvement helps with testing, isolation, nursing care, and realistic planning.

EHM is caused by infection with EHV-1, a contagious equine herpesvirus. The virus usually spreads through respiratory secretions, direct nose-to-nose contact, shared water sources, contaminated buckets, tack, twitches, thermometers, trailers, and the hands or clothing of people moving between animals. Outbreaks are more likely where equids mix closely, such as boarding facilities, shows, sales, rescues, breeding farms, and multi-equid properties.

Not every donkey exposed to EHV-1 develops neurologic disease. Many infected equids have mild respiratory signs, fever, or no obvious signs at all. In some animals, the virus enters the bloodstream and damages small blood vessels in the central nervous system. That vascular injury is what leads to spinal cord and brain dysfunction.

Stress appears to matter. Transport, weaning, crowding, recent illness, and other immune stressors may increase viral shedding or reactivation from latency. Because donkeys often show pain and illness less dramatically than horses, early changes can be easy to overlook until weakness becomes more obvious.

Your vet will start with a physical and neurologic exam and ask about fever, travel, new arrivals, recent events, and whether any horses, donkeys, or mules on the property are sick. Because several conditions can cause weakness or ataxia in donkeys, your vet may also consider differentials such as trauma, equine protozoal myeloencephalitis, West Nile virus, cervical spinal disease, toxicities, or severe metabolic illness.

Testing for suspected EHV-1 usually includes PCR on a nasal or nasopharyngeal swab and PCR on whole blood collected in EDTA. These tests help identify active infection or viremia. Bloodwork may be used to assess hydration, inflammation, and organ function. In selected cases, your vet may discuss cerebrospinal fluid collection, especially when the diagnosis is unclear or other neurologic diseases are high on the list.

A negative test does not always rule EHM out, especially if timing or sample quality is not ideal. That is one reason your vet may recommend repeat testing, isolation, and close monitoring of exposed equids even while results are pending. If there is concern for an outbreak, your vet may also involve the state animal health official and advise movement restrictions.

Prevention starts with biosecurity. Isolate new arrivals, avoid shared buckets and tack between groups, wash hands between animals, and clean thermometers, lead ropes, twitches, and trailers after use. If any equid develops fever, nasal discharge, weakness, or urinary changes, separate them immediately and call your vet before moving them around the property.

Routine temperature monitoring is one of the most practical tools during a suspected exposure. Your vet may recommend taking temperatures once or twice daily in exposed donkeys, horses, and mules for a defined period. Limiting traffic on and off the property, assigning separate equipment to isolated animals, and handling healthy animals before sick ones can reduce spread.

Vaccination is worth discussing with your vet, but it is important to set expectations. Current equine herpesvirus vaccines are used to reduce respiratory disease and abortion risk associated with EHV-1 and EHV-4, yet there is no licensed vaccine specifically labeled to prevent the neurologic form, EHM. Vaccination may still be part of a herd health plan, especially on properties with frequent movement or mixing, but it should be paired with strong biosecurity rather than relied on alone.