Equine Viral Arteritis (EVA)

EVA

In South Africa, the disease that we most fear is African Horse Sickness. This endemic disease has led to worldwide restrictions on South African horses and remains a concern for horse owners in South Africa. However, in light of the international issue, we decided to focus on equine viral arteritis (EVA), a disease that was first identified in 1953 and is rife worldwide.

What is equine viral arteritis?

EVA is a viral disease that was first discovered during the early 1950s. EVA is caused by the spread of an arterivirus (a genus of viruses in the arteriviridae family) called equine arteritis virus (EAV). The virus can be transmitted through the horse’s respiratory system, meaning that he inhales the virus and consequently becomes infected, but it can also be sexually transmitted either by live covering or artificial insemination (AI).

Although the disease was discovered in the early 1950s, it wasn’t until 1993 that the first case was confirmed in the United Kingdom, after a bunch of mares were bred to an infected stallion who had been brought into the UK from Poland. Although testing was conducted for the virus, the horse had tested negative for EVA before being imported.

Today, the infection affects horses worldwide, and some breeds are more susceptible to EVA than others, namely Thoroughbreds, Standardbreds and Warmbloods.

Symptoms and treatment of EVA

Signs that a horse has been infected with EVA include:

  • Fatigue
  • Fever
  • Nasal discharge
  • Skin rashes
  • Conjunctivitis (‘pink eye’ or swelling of the inner eyelid lining)
  • Oedema
  • Abortion in pregnant mares

Degrees of severity can differ hugely and some horses don’t show any signs of sickness. Fortunately, most horses’ bodies can fight the infection themselves and the majority of adult horses make a full recovery. In some cases, additional treatment such as antibiotics or anti-inflammatories may be necessary.

The problem with stallions

As mentioned, some horses don’t show any symptoms and therefore it becomes unlikely that anyone will detect that the horse has EVA. If a stallion does not become clear of EVA within a few weeks of infection, he can become a carrier. The stallion will then transmit the virus to broodmares, which is then passed on to the foal. The virus is dependent on testosterone, so immature colts won’t become carriers. Castration further prevents transmission of the virus.

Control measures

EVA is not listed as a reportable disease in the United States. There are no recommended ‘best practice’ approaches put in place to limit the spread of the disease, but there are issued guidelines that can be researched to prevent the spread of EVA. In the UK and select European countries, the matter is taken more seriously and more strict regulations are in place. In 1995, the UK government passed the law that EVA must be reported if a stallion is EVA positive, if a stallion is seropositive (meaning that he has antibodies against EVA), if EVA has been detected in a mare within 14 days of live cover or AI, or if the virus has been detected in a semen sample.

Since the virus affects Thoroughbreds, the respective racing associations and boards require that vets and owners conduct blood tests on mares and stallions after 1 January of each year, that stallions are vaccinated against EVA twice a year, that mares are tested within 28 days before breeding, and that imported horses are tested within 28 days of arrival. The British Equine Veterinary Association has also issued guidelines on preventing the spread of EVA during AI. These guidelines specify that blood tests be conducted before buying or importing a breeding horse and ensuring that the horse tests negative. Breeders should also test semen to ensure it is EVA-free.

The challenge among the European countries is that there are varying attitudes towards the severity of EVA. Some breeders are not concerned about the virus, whereas others are. It’s up to horse owners to employ best practice and protect their own horses against the virus.

Did you know?

New Zealand is EVA-free

The full article appears in the August INTERNATIONAL ISSUE of HQ  > Shop now