Equine herpesvirus (EHV)

Horses can suffer from a number of viral diseases, EHV is just one of many. If you are considering breeding your horse you should be aware of this disease and how it can affect breeding status as well and your horse’s general health and well-being. EHV is the most commonly diagnosed cause of infectious abortion in pregnant mares.

Equine Herpesvirus (EHV) is a highly infectious viral disease that can affect any horse at any time and may recur after just a few months.
EHV is widely acknowledged as a major cause of respiratory disease, and is the most commonly diagnosed cause of infectious abortion in pregnant mares, it can also cause paralysis.

EHV is spread from horse to horse, mainly through the infective virus being coughed into the air and inhaled by other horses close by. Once infected with EHV, horses become carriers of the disease. Although they may show no symptoms themselves, they can intermittently shed the virus and infect other horses in the area. Excitement or stress can often cause shedding – horses travelling to events/competitions are particularly at risk.
EHV occurs throughout the UK.

As with many other viral conditions, the first sign is usually a fever, where the temperature can rise as high as 41°C (106°F). Other signs include:

  • A dry cough – often less harsh than that seen with ‘flu’
  • Depression/lethargy
  • Nasal discharge – watery to thick
  • Ocular discharge
  • Swelling and hardening of the sub-mandibular lymph nodes (under the jaw)

If you notice any of these signs and think your horse may be infected with EHV call your vet immediately. Not all of these signs are caused by EHV, therefore your vet may need to take blood samples and swabs to establish the exact cause of illness.
Your horse may develop viral pneumonia, which can be fatal for foals. Secondary infections with bacteria may occur leading to bronchopneumonia.
EHV can also causes abortion of unborn foals, this usually occurs in the last half of pregnancy and the foal is usually born dead. Foals infected in the womb, and born alive, usually die shortly after birth.

Your horse will be ill for some weeks before it is fit enough to resume a normal exercise regime.
Unfortunately, natural infection does not stimulate much immunity against re-infection, therefore your horse may become infected again after just a few months. Once infected, many horses become carriers which means they will shed the virus, infecting other in-contact horses.
EHV also causes immunosuppression, which means your horse’s ability to fight off infection will be reduced, which may lead to infections with other viruses and bacteria causing further suffering and loss of use.

Your horse can be vaccinated against EHV, which will help prevent disease and reduce the amount of virus shed to in-contact horses. Vaccination against EHV usually starts from 5 months of age, with two vaccinations given 4-6 weeks apart, and then regular boosters every 6 months.
Your vet will be able to explain further the vaccination programmes available to help in the prevention of the respiratory forms of the disease and to aid in reducing the risk of abortion cause by EHV infection.
Vaccination alone is not enough to prevent infection, management also pays a major role in preventing and controlling the disease, ie good stable management (hygiene), prevention of over-crowding, avoiding stress and isolation.
Contact your vet for further advice.