What is Equine Herpesvirus?

Generic virus illustration

Generic virus illustration

By XL Equine

Equine herpesvirus (EHV) is a contagious viral infection which can cause respiratory disease, abortions and neurological disease in horses. There are two main types of EHV which cause disease:
• EHV-4 is very common and causes respiratory disease;
• EHV-1 is less common, but can have severe effects, causing abortion and neurological disease.
Most horses are first exposed to the disease as youngsters, with the vast majority of our horses exposed to EHV throughout their lives. The effects of disease on a breeding establishment can be devastating, but even on livery or competition yards, entire seasons can be compromised due to EHV infection affecting performance and well-being.

What are the symptoms?
In respiratory disease the clinical symptoms may include a rise in body temperature, nasal discharge and a dry cough in younger horses. The horse may also show signs of depression and lethargy. However you can commonly have a disease scenario with no obvious symptoms, just depressed performance or recurrent airway infections in the horses. In breeding mares, EHV-1 is the most commonly diagnosed cause of infectious abortion. Abortion usually occurs in the last third of pregnancy, but as a previous infection can leave a horse as a carrier, there may be no clinical signs prior to abortion. Very rarely EHV-1 infection can cause a neurological disease – horses may become paralysed and are given a very poor prognosis.

How is EHV transmitted?
EHV is a highly contagious viral disease. It passes from horse to horse through the respiratory tract as viral particles are breathed in from infected horses. Once a horse is infected with EHV, it can harbour the virus throughout its life and potentially ‘shed’ the disease to other animals. Horses shed EHV at times of stress, for example moving yards or when under other disease challenge. The main concern for the equine population is the way the disease persists in our horses and, since natural immunity is short-lived, horses can remain at risk from EHV despite previous exposure. This is why ongoing control and vaccination are so important.

What can I do to prevent my horse getting EHV?
Control of EHV-1 and EHV-4 is based on prevention and limiting the spread of disease if it occurs.
• Stable management, in particular when dealing with potentially infected horses, is key to the control of the disease. Try to minimise stressful situations for your horses as much as possible and isolate sick or new horses.
• Vaccination can play a big role; vaccinating your horse will help reduce the severity of clinical signs. But perhaps more importantly vaccination can reduce the spread of the EHV by reducing the amount of infective virus that is shed onto other in-contact horses.

Vaccination is more effective when enough horses are covered for a ‘herd immunity’ strategy to work. The same collective principle is true of management strategies. A yard approach is the best way to manage the threat of this common disease – discuss it with your vet for help and information on the best approach for your horses.

Author: The Editor

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