Equine Herpesvirus Respiratory Disease in Donkeys: EHV-1 and EHV-4

Equine herpesvirus respiratory disease is a contagious infection caused mainly by EHV-1 and EHV-4, two closely related herpesviruses that affect equids. Although much of the published research focuses on horses, donkeys are also equids and can be infected. EHV-1 has the broader disease range and can affect most equids, while EHV-4 is primarily associated with respiratory disease.

In the respiratory form, the virus infects the upper airway and nearby lymph nodes. Donkeys may develop fever, nasal discharge, cough, swollen lymph nodes, low energy, and reduced appetite. Some infected animals have mild signs, while others can spread virus before the illness is obvious.

One reason EHV is tricky is that herpesviruses can become latent, meaning the virus stays in the body after recovery and may reactivate later during stress, transport, crowding, illness, or other immune challenges. That is why outbreaks can appear even in groups with no recent obvious exposure.

For most donkeys with uncomplicated respiratory disease, the outlook is fair to good with supportive care and strong biosecurity. Still, EHV-1 deserves extra caution because it can also be linked to abortion and neurologic disease in equids. Your vet can help sort out the level of risk for your donkey and the rest of the herd.

This disease is caused by infection with equine herpesvirus-1 or equine herpesvirus-4. The viruses spread mainly through respiratory secretions. Direct nose-to-nose contact is a common route, but contaminated buckets, tack, trailers, stalls, clothing, and hands can also move virus between animals.

EHV-1 is especially important because it can infect most equids and is associated not only with respiratory disease, but also abortion and neurologic disease. EHV-4 is more closely tied to respiratory illness. The incubation period is usually about 2 to 10 days, so a recently exposed donkey may look normal for several days before signs appear.

Like other herpesviruses, EHV can go dormant after infection. A donkey or horse that recovered months or years ago may still carry latent virus. Stressors such as transport, weaning, crowding, poor ventilation, illness, or heavy training can contribute to reactivation and viral shedding.

That means outbreaks are not always caused by a newly introduced sick animal. Sometimes a clinically normal equid begins shedding virus after stress, and the infection then spreads through a susceptible group. Good biosecurity matters even when every animal appears healthy.

Your vet will start with the history and physical exam, including temperature, nasal discharge, breathing pattern, lymph node size, and any herd-level concerns. Because fever can come before obvious respiratory signs, recent travel, new arrivals, event attendance, or contact with sick equids are important clues.

The main test used today is PCR, usually performed on a nasal swab and sometimes whole blood. PCR is the preferred rapid test during suspected outbreaks because it can detect viral genetic material quickly. A nasal swab helps show whether the donkey is shedding virus, while blood testing may help identify EHV-1 viremia in some cases.

Your vet may also recommend a CBC, fibrinogen, or other supportive lab work to look for inflammation, dehydration, or secondary problems. If there is concern for other respiratory diseases, a broader equine respiratory PCR panel may be more useful than a single test.

A negative test does not always fully rule EHV out, especially if sampling happened early, late, or between shedding periods. In some situations, your vet may repeat testing in 24 to 72 hours, especially if fever persists or other equids on the property become ill.

Prevention depends on biosecurity, isolation, and vaccination planning with your vet. New arrivals and equids returning from shows, sales, rescues, breeding farms, or shared transport should be kept separate before joining the resident group. Current equine guidance commonly recommends about 21 days of isolation for new or returning animals, with twice-daily temperature checks because fever may be the earliest sign.

If a donkey develops fever, nasal discharge, cough, or lethargy, separate that animal right away and use dedicated buckets, feed tools, tack, and grooming items. Handle isolated animals last if possible, and wash hands or change gloves and outerwear between groups. Good ventilation, lower stocking density, and reduced stress also help lower transmission risk.

During a confirmed or strongly suspected outbreak, your vet may recommend a longer restriction period. Published equine guidance commonly uses 28 days after recovery of the last clinical case or a risk-based release plan that includes testing and state requirements where applicable. EHV-1 is reportable in many U.S. states, so your vet may need to coordinate with animal health officials.

Vaccines for EHV-1 and EHV-4 are available for equids, but they do not provide complete protection and no licensed vaccine has a label claim for preventing the neurologic form of EHV-1. Even so, vaccination can still be part of a herd-risk strategy to reduce respiratory disease and viral shedding. Your vet can help tailor a schedule for donkeys living with horses, breeding animals, or frequently traveling equids.