Viral diseases

Equine Viral Arteritis - Causes, Symptoms and Treatment

Laura García Ortiz
By Laura García Ortiz, Veterinarian specialized in feline medicine. Updated: February 28, 2024
Equine Viral Arteritis - Causes, Symptoms and Treatment

See files for Horses

Equine viral arteritis, also known as EVA, is a disease of horses caused by a virus of the species alphaarterivirus equid, an RNA virus. The virus that causes EVA was first isolated in 1953, but the disease has affected horses worldwide for centuries. In the United States, it has been more common in some breeds of horses, but there is no breed "immunity." It is usually associated with racetracks and breeding or rearing facilities for this species. In general, the virus rarely causes severe forms, let alone high mortality rates, but certain age and risk groups tend to be more at risk.

In this AnimalWised article, we address equine viral arteritis, its symptoms, diagnosis, and treatment.

You may also be interested in: Most Common Viral Diseases in Cats
  1. What is equine viral arteritis?
  2. Causes of equine viral arteritis
  3. Symptoms of equine viral arteritis
  4. Diagnosis of equine viral arteritis
  5. Treatment and prevention of equine viral arteritis

What is equine viral arteritis?

Equine viral arteritis (EVA) is a contagious viral disease in horses caused by equine arteritis virus (EAV). EVA Is caused by an arterivirus called equine arteritis virus (EAV). Arteriviruses are small, enveloped animal viruses with an icosahedral core containing a positive-sense RNA genome. It primarily affects the placenta or respiratory system and causes abortions or inflammatory lesions in the arterioles of animals with acute infection.

The disease primarily affects horses, but alpacas and llamas may also be affected. The disease is not transmitted to humans and is therefore not considered a zoonosis.

The symptoms that occur depend on the age of the horse, the strain of the infectious virus, the condition of the horse, and the route of infection. Most horses with EVA infection show no signs; when a horse does show signs, they can vary greatly in severity. The most severe forms of the disease, which can end the horse's life, usually occur in very young foals or foals with congenital disease, but also in immunocompromised horses or horses with other pathology.

Causes of equine viral arteritis

There are a number of routes of transmission for the virus, but the most common is the respiratory route. Routes for transmission are as follows:

  • EVA is spread from acutely infected horses through respiratory secretions in close contact environments (racetracks, shows, sales, etc.).

  • The virus is also transmitted through breeding (natural or artificial insemination). Infected stallions excrete the virus through semen and can serve as long-term carriers.

  • Fomites (equipment such as buckets, brushes, shoes, and people) are another source for spreading the virus.

  • The disease can also be transmitted congenitally from mother to offspring.

Read this other article about how horses mate to learn more about horse reproduction.

Equine Viral Arteritis - Causes, Symptoms and Treatment - Causes of equine viral arteritis

Symptoms of equine viral arteritis

In the pathogenesis of equine viral arteritis, the virus multiplies in the arterioles and causes edema and cell death (necrosis). Clinical signs occur after an incubation period of 3-14 days, earlier if infection is respiratory, and later if transmission has occurred through sexual intercourse.

Once the disease breaks out, the following clinical signs may be observed:

  • Fever
  • Depression
  • Anorexia
  • Constipation of the mucous membranes
  • Petechiae
  • Conjunctivitis (inflammation of the conjunctiva)
  • Epiphora (lacrimation)
  • Runny nose
  • Moderate cough
  • Dyspnea (shortness of breath)
  • Stomatitis
  • Diarrhea (diarrhea)
  • Colic
  • Urticaria
  • Edema of the prepuce, scrotum, or mammary gland
  • Periorbital or supraorbital edema
  • Edema in distal areas, especially the hind limbs
  • Abortions when there is massive fetal infection and necrosis of the placenta

Horses usually excrete the virus 28 days after disease, but in adult males it is very persistent in the prostate and seminal vesicles, making them infectious even for life.

What injuries does it cause in the organs of a sick horse?

Injuries that occur in the organs of horses show a clear injury to the blood vessels. Specifically, disseminated vasculitis causes hemorrhage, congestion, and edema, especially in the subcutaneous tissues of the abdomen and extremities as well as in the peritoneal, pleural, and pericardial fluids.

Pulmonary edema, emphysema, interstitial pneumonia, intestinal inflammation, and infarcts in the spleen have been observed in foals that die from this virus.

Diagnosis of equine viral arteritis

Because of the variability of symptoms, the only sure means of diagnosing EVA is a laboratory test. The virus can be detected in various tissues and fluids, such as:

  • Nasal or conjunctival secretions
  • Semen
  • Blood
  • Placenta
  • Fetal fluids
  • Tissues

However, blood is usually tested for the presence of antibodies to the virus.

Samples for testing should be collected as soon as possible after the horse becomes ill to increase the likelihood of confirming the diagnosis. Screening for carrier status in the stallion includes initial serologic testing to determine whether or not the stallion has antibodies to EAV. If the horse is seropositive, a semen sample containing the sperm-rich fraction of the ejaculate should be tested for evidence of the virus. Your veterinarian will tell you which laboratories can detect EAV infection.

Equine Viral Arteritis - Causes, Symptoms and Treatment - Diagnosis of equine viral arteritis

Treatment and prevention of equine viral arteritis

Treatment is symptomatic and focuses on reducing swelling and inflammation and eliminating edema in patients with severe clinical symptoms. Rest and proper care contribute to healing in most cases.

Proper control and prevention of the disease must always be done with a series of preventive measures. This is to reduce the spread of the virus in breeding horse populations, to minimize the risk of abortions and deaths in young foals, and to determine carrier status in stallions and foals. The control measures are:

  • Semen analysis prior to stabling new stallions.

  • Quarantine of new stallions.

  • Good management in horse breeding farms.

  • Identification of carrier horses.

  • Isolation of horses with clinical signs.

  • Vaccination depending on the country.

  • Good hygiene and biosecurity during the breeding season.

Vaccine for equine viral arteritis

There are mainly two types of vaccines to combat this disease, namely:

  • Modified live vaccine: consists of attenuated microorganisms that multiply in vivo to produce an immune response similar to that of natural infection, but without the associated clinical symptoms typically seen with natural exposure to the specific pathogen. It is considered safe and effective for males, empty mares and foals. However, it should not be given to pregnant mares in the last two months of gestation or foals less than 6 weeks of age unless there is a high risk of infection. It protects against EVA for 1 to 3 years, but does not prevent reinfection or virus replication.

  • Inactivated vaccine: consists of virus particles, bacteria, or other pathogens that have been grown in culture and then killed to destroy the disease-producing capacity. Use of this vaccine is safe in pregnant mares, but does not produce as strong immunity as the previous vaccine. Two or more doses are required to achieve a good response with neutralizing antibodies.

It is advisable to vaccinate foals at 6 to 12 months of age before there is a risk of contracting the virus.

Mares mated to known infected or carrier stallions or to semen containing EVA should be vaccinated. Prior to breeding season, stallions that are not virus carriers should be vaccinated, and vaccination records should be maintained.

After vaccination, it is possible for virus to be excreted, so vaccinated horses should be isolated for a period of time.

If you want to improve your relationship with your horse and understand them better, read this other article about communication with horses. Although horses use these techniques to communicate with other horses, they also communicate with other animals and humans.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Equine Viral Arteritis - Causes, Symptoms and Treatment, we recommend you visit our Viral diseases category.

  • E. Perozo. (2006). Equine Viral Arteritis: A Review. Available at:
  • OIE. Equine Viral Arteritis (Equine Arteritis Virus Infection). Available at:
  • PJ Timoney. IVIS (2003). Equine Viral Arteritis . Available at:
  • Ministry of Agriculture, Government of Chile. (2020). Technical sheet Equine Viral Arteritis (AVE). Available at:
Write a comment
Add an image
Click to attach a photo related to your comment
What did you think of this article?
1 of 3
Equine Viral Arteritis - Causes, Symptoms and Treatment