Equine Herpes Virus (EHV) is a highly contagious airborne disease. There are nine strains of EHV, but EHV-1 and EHV-4 are the most common and occurs in horses worldwide.
EHV-1 causes respiratory disease (especially in young horses), pregnant mares to abort and neurological disease in horses of any age, sex and breed. Young foals are also at risk and can die from the infection.
EHV-4 causes respiratory disease and occasionally risks abortion.
Not all horses with EHV show the same signs, some may only show mild signs or if they are silently carrying the virus potentially no signs at all. A high temperature is often the first indicator that your horse is unwell. If you’re not sure how to take your horse’s temperature, please watch our video below.
If you notice your horse is showing signs of ill-health, isolate them and contact your vet immediately. In most cases, horses will make a good recovery from respiratory disease, but the prognosis for those with the neurological disease can be very variable. If EHV is suspected, your vet will take a nasopharyngeal swab and potentially a blood sample from your horse. All horses that have had direct, or indirect contact with the infected horse should be closely monitored and their temperatures taken twice a day and isolation procedures put in place.
Once infected, horse can show signs of disease within 24 hours, but is usually within 4-6 days. For some horses this may be longer.
Clinical signs of EHV-1 and EHV-4 respiratory disease are very similar to equine flu and can include:
- A high temperature
- Nasal discharge
- A dry cough
- Loss of appetite
- Reduced performance
EHV-1 can cause severe disease of the nervous system. Affected horses can appear weak, may not be able to pass urine or droppings, display signs of poor limb coordination (the hindlimbs are more usually affected) and in severe cases are unable to stand. These signs occur as the virus damages the spinal cord. Outbreaks of this strain are normally rare.
Pregnant mares can suddenly and unexpectedly miscarry their unborn foal.
Further information about abortion caused by EHV-1, the measures that can be taken to prevent the disease or steps to take in the event of an outbreak can be found here.
As long as there are no complications, horses with respiratory disease should usually make a good recovery within a few weeks.
Neurological disease can understandably cause significant concern and panic for horse owners. With any disease outbreak it is critical that there is clear communication with the vets (if multiple practices are involved), horse owners and neighbouring yards in the area. Horses with more severe neurological signs and those that are unable to stand, may need to be euthanised on welfare grounds. For less severe cases, recovery is likely to take several months.
How the disease is spread
EHV is a contagious viral disease which can be spread via direct horse to horse contact (for example horses touching noses) and aerosol droplets over short distances (up to 5 metres) by coughing and snorting which can result in rapid spread through a group of horses. It can also be spread indirectly by shared equipment such as tack, feed bowls and people via their hands and clothing.
When mares miscarry due to EHV, their foal, associated fluids and discharges expelled are all sources of infection to other horses.
EHV can lie dormant in the horse following first infection, meaning they will carry the virus as a ‘silent’ infection. The horse will often appear healthy and show no signs of disease, but occasionally the disease can reoccur at intervals throughout its life. The virus can be reactivated during stressful conditions, such as travelling, moving yards or attending a competition. The horse will shed the virus but may not show any signs that they are ill.
As the disease can spread easily and has the potential for serious consequences, the BHS strongly recommends that yards inform others if they have an outbreak so potential in-contact horses can be quickly isolated and monitored to help decrease the risk of spread. If you have any concerns for your horse contact your vet immediately.
Be vigilant if you have pregnant mares on your yard and speak to your vet for advice.
Good health and hygiene methods are essential, including an effective quarantine procedure for new arrivals. Read our advice and the simple steps you can take to prevent the spread of disease.
If you are travelling horses or receiving horses from Europe, specific biosecurity guidance has been issued by the British Equestrian Federation and British Showing.
Vaccinating your horse can help prevent both respiratory disease and abortion caused by EHV-1 and/or EHV-4. There is no vaccine registered to prevent EHV-1 neurological disease.
Vaccination is especially recommended for horses under the age of five as they may be particularly susceptible to respiratory disease caused by EHV-1. Vaccination can also help reduce the amount of virus shed by an infected horse. Speak to your vet for advice on the EHV vaccine.
Vaccinations are part of an important tool to help prevent disease, but it’s important to always maintain good health and hygiene practices.
More information on EHV is available from:
The Horserace Betting Levy Board (HBLB) EHV Code of Practice
In partnership with Professor Josh Slater, Horse Dialog have produced a series of videos to highlight the key facts of EHV that horse owners need to be aware of. The videos are available to watch from the following links:
What is EHV?
Types of EHV and signs to look out for
What to do if you suspect EHV
EHV Vaccination and how it works
In addition, these videos by Dr David Rendle on Horse Dialog Facebook Video Player are also helpful:
Neurological form of Equine Herpes Virus. What is it?
Reducing the risk of neurological EHV