Equine Influenza: Symptoms, Treatment, and Prevention

Equine influenza virus (EIV) is a highly contagious respiratory disease in horses. It’s important for all horse owners to understand the symptoms of the illness and how to help prevent its spread.

What Is Equine Influenza?

Equine influenza is a respiratory virus that spreads easily through direct and indirect contact with infected horses, which may include:

• Horse-to-horse contact

• Contact through clothing, equipment, or brushes

Equine influenza circulates in the United States at low levels, especially from November through March, much like influenza viruses in humans.

Outbreaks are more likely to occur in large groups of horses, such as at horse shows, events, and races. Generally, the younger population (1–5 years old) is more susceptible to the virus, but horses of any age can be infected.

While equine influenza is not considered a medical emergency, it does often require working with your veterinarian, and quick biosecurity measures like quarantining sick horses can help prevent the disease from spreading.

Equine Influenza Symptoms

With a short incubation time of one to three days on average, equine influenza can spread quickly at an event or barn.

Common symptoms of equine influenza include:

• Coughing

• Fever

• Nasal discharge

• Lethargy

• Loss of appetite

• Weakness

A horse may also be asymptomatic, with no signs of disease, but they can still spread the virus.

Causes of Equine Influenza

Infection via direct contact between horses occurs most commonly when infected horses release viral particles into the air by coughing or snorting. These particles can travel up to 150 feet and come in contact with other horses.

Infection by indirect contact between horses can occur when brushes, buckets, and other equipment are shared among horses or when people transmit viral particles from their own clothing or shoes to other horses.

How Veterinarians Diagnose Equine Influenza

Several respiratory diseases in horses can look similar, so it’s hard to diagnose equine influenza based solely on symptoms. Your veterinarian may do testing to diagnose the infection.

There are two types of tests they may recommend:

1. PCR testing via a nasal swab can identify equine influenza antigen

2. ELISA testing via a blood sample to look for antibodies or proteins that the horse makes in response to the virus

Testing must be done at the onset of disease and again two weeks later (for blood testing). If testing is delayed for either test, false negative results can be seen.

Equine Influenza Treatment

For most horses, equine influenza is a mild respiratory illness. Treatment will include rest and supportive care, such as fluids for dehydration and NSAIDs (Banamine, phenylbutazone) to lower fever if present.

In some cases, a horse may have a persistent fever, nasal discharge, or develop pneumonia, and will need prescription medications such as antibiotics.

Horses can gradually return to their normal activities once all symptoms have resolved.  

Recovery and Management of Equine Influenza

If one horse in a barn is suspected of any respiratory illness, they should be quarantined away from other horses. It’s recommended to start checking the temperatures of other horses in the barn daily so you can catch it early if anyone else develops symptoms.

Any quarantined horses should be handled last, with their own equipment that is not shared among other horses.

Horses with mild infections typically recover in two to three weeks. In severely affected horses, it may take up to six months to fully recover.

Prevention of Equine Influenza

The best preventative for equine influenza in horses is vaccination. If a vaccinated horse gets the disease, they generally are less severely affected and shed the virus for fewer days.

With proper vaccination and biosecurity, horse owners can minimize the risk of infection.

In the presence of an infection, you can reduce the spread of the virus by taking temperatures of all horses in a barn twice daily and isolating horses quickly.

Thoroughly cleaning all equipment and washing all common areas can also help to reduce the spread of disease.  

By using your own equipment when away from home, you can also help reduce the risk of infection.