Equine Herpes Virus
What it is
Equine herpes virus (EHV) is the cause of a contagious disease that circulates in most parts of the world and can be responsible for serious, widespread illness in horses
Of the four main types, EHV-1 and EHV-4 are the most common in the UK.
- EHV-1 which can cause signs of respiratory disease in young horses (runny nose, coughing, raised temperature), abortion in pregnant mares (usually later in pregnancy and sometimes in large outbreaks involving multiple mares) and sometimes paralysis in horses (of all ages). The virus affects young horses more than older ones. Older horses are less likely to show signs of infection but are just as likely to spread the virus
- EHV-4 which usually only has a minimal effect on breathing and can occasionally cause abortion
- EHV-3 which is a reproductive disease that causes pox-like lesions on the penis of stallions and the vulva of mares
- EHV-5 which is associated with an unusual type of lung condition in adult horses
Most horses will first encounter the virus as a foal and following recovery, the virus can remain in the body, in an inactive state, known as viral latency. In the future, the latent virus in a horse can ‘reactivate’ and spread to infect other horses. Reactivation is most commonly associated with times of stress, such as moving yards or going to competitions.
EHV outbreaks occur in the UK and are usually restricted to a single premises, however, multiple premises can be involved following mixing of horses from different yards, such as at equine competitions. Most horses may have mild respiratory signs or no signs of infection, but, unpredictably, some occurrences can result in widespread infection on a yard and very sick horses.
How it is spread
EHV can be transmitted through direct contact between horses, such as touching noses over a stable door, or by indirect contact, such as nasal discharge from a horse being on our hands and then we touch another horse without washing our hands first. EHV can also spread in the air, following a horse coughing or sneezing, but the virus is thought to only be able to spread up to a matter of metres.
This method of spread is most likely to occur when horses are in close contact or housed in enclosed airspaces, especially with poor ventilation. There is the possibility for infectious horses to spread EHV without having any obvious clinical signs of disease (i.e. they are subclinically infected), potentially leading to exposure of horses prior to awareness of an infection circulating.
Signs of EHV
EHV-1 and EHV-4 can both cause respiratory signs including a snotty nose, coughing and a temperature.
Signs of EHV can include
- Nasal discharge
- Coughing
- Fever (≥ 38.5°C)
- Lethargy / poor performance
- Loss of appetite
- Neurological signs - ranging from mild to severe, including recumbency often requiring euthanasia
- Abortion / neonatal foal death
Most commonly, EHV-1 is the strain that can cause neurological signs such as bladder incontinence, limb weakness, incoordination, recumbency and an inability to rise. EHV-1 can also cause pregnant mares to abort their foal or infected foals to be born weak and the disease is usually fatal in them. EHV-4 is also occasionally associated with abortion as well as respiratory disease.
Biosecurity
Implementing sensible everyday hygiene measures will help to reduce the spread of infection on your yard if disease strikes.
Examples include
- Keeping horse groups the same (ensure the same horses are stabled and turned out together, i.e. have defined yard groups and don’t mix them up)
- Wash hands between horses/horse groups
- Keep separate designated equipment for each horse and group
- Don’t share tack between horses
- Encourage visiting personnel to wash their hands as a minimum on arrival
Have a yard vaccination policy
An EHV vaccine is licensed to reduce clinical sign severity, duration and viral shedding of respiratory disease and abortion presentations. However, there is currently no licensed vaccine available to prevent neurologica disease. We do not advise vaccinating horses that have had recent potential contact with a case of EHV.
Plan how to manage sick horses
Plan where they can be isolated, how hygiene measures will be implemented (separate dedicated equipment, muck heap and carers) and have thermometers available to twice daily monitor temperatures of all in contact horses.
Plan how to manage new arrivals
Quarantine new arrivals for a minimum of 2 weeks - keep them physically separated and use separate equipment and carers/deal with them last.
Monitor them during quarantine; visually checking for nasal and ocular discharges, lymph node enlargement and leaving of food. Listen for coughing and record rectal temperature twice daily.
Contact your vet if any signs of infection are noted.
Use biosecurity measures when out competing
Avoid direct contact with other horses and indirect contact as much as possible. Take your own equipment, including water and buckets, and don’t graze horses in communal areas. If stabling overnight, monitor and record rectal temperature twice daily and have good separation from other horses. Ensure all old bedding was removed and the stable disinfected between horses. Ideally quarantine horses on returning home and monitor for up to two weeks (temperature and clinical signs).
