Equine viral arteritis (EVA) is known to be highly contagious disease and generally results in respiratory problems in horses. The infection is caused by the equine arteritis virus (EVA) and animals, other than those from the equine family, are not affected by the disease since this particular virus is species specific. Although a rare occurrence, death for newborn foals can sometimes result from an infection when it is the mother that becomes infected a few days before the foal’s birth. The virus replicates itself in respiratory system and then travels to the lymph nodes and other tissues. The main carriers of the disease are said to be stallions. The equine arteritis virus is transmitted through aerosol droplets or mating and symptoms include fevers and even abortions in pregnant mares. It is not known for humans to be affected by equine viral arteritis and so is not zoonotic. Unfortunately, there is no cure for this fairly detrimental disease although vaccinations are currently available.
Direct contact is usually required for the transmission of the equine arteritis virus as it enters the respiratory tract of the animal via infected aerosol droplets through coughing. Mating can be another source of transmission as well as contact with an infected dead foetus following abortion. Additionally, contaminated surfaces including clothing, footwear and tack can also transmit the disease.
Breeding stallions, and also teasers, are able to act as carriers and so often studs are advertised as “EVA vaccinated and tested negative”. The disease is transmitted, here, via sexual intercourse and ejaculation. Even cooled and frozen semen used for artificial insemination (AI) can spread the disease. Stallions are able to shed the equine arteritis virus for many years, after recovery, and not show any symptoms. Since a certain level testosterone is necessary for the shedding of equine viral arteritis, geldings are not thought to be a source of infection as carriers or shedders unless the disease has progressed to an acute infection.
The same is also true for mares since, despite the fact that they may have been infected, a lack of testosterone means they are not known to be carriers and so it could be argued that they transfer the virus to a lesser extent than stallions.
The milder symptoms present themselves as a high temperature, nasal discharge, conjunctivitis, lethargy, depression and occasionally swelling of some areas. The swelling occurs in regions around the lower limbs, the reproductive organs and the eyes and is called an oedema. Some horses do not show any symptoms, these are known as asymptomatic, whilst still spreading the virus. While some mares may contract the disease, there may be no knowledge of infection, despite a possible abortion, from the owner but the mare may even gain immunity from it for a short period of time following recovery. Equine viral arteritis can even cause abortion in pregnant mares.
Treatment and Prevention
There is no cure for equine viral arteritis and only supportive treatment can be given. Vaccines are available although some countries have banned its use. Horses aged as young as nine months old can initially be given the vaccine. Boosters are then able to be administered twice yearly. Before vaccination the horse must provide a negative result to the presence of equine arteritis virus following certain blood tests.
Diagnosis and Prognosis
Equine viral arteritis can be diagnosed via the taking of blood samples although vaccinated horses may show a positive result despite not being infected. Other samples which can be taken are semen and sometimes urine. The difference in methods is what is looked for in each of the samples. To confirm infection, for example, the blood can be searched for both the equine arteritis virus and the antibodies whereas the semen can only present the virus rather than the antibodies. The polymerase chain reaction (PCR) test may be used to identify the virus. Aborted foetuses are also used for testing. The disease is rarely fatal with the exception of very young foals.