Equine Influenza, more commonly known as the flu, is one of the most common respiratory infectious diseases. It is caused by an RNA virus and is highly contagious but rarely fatal.

Incubation: The incubation period is the time from exposure to the virus to when a horse shows clinical signs of infection. The incubation period for equine influenza ranges from 24 hours to three days.

Transmission: The most common method of transmission is airborne droplets released by coughing and/or nasal discharge. The virus can spread a significant distance (up to 150 feet or 50 yards). The virus can also be spread through contaminated surfaces such as clothing, vehicles, grooming supplies, and stalls.

Shedding period: Respiratory shedding typically lasts for seven to ten days post-infection in horses who were infected for the first time or were unvaccinated. Shedding period is much shorter (about three to five days) in partially immune horses (previously infected or vaccinated).

Clinical Signs: Clinical signs include a fever up to 106 ºF, lethargy, dry harsh to hacking cough (which can last up to six weeks), and nasal discharge (initially clear and watery and becomes yellow or white with secondary bacterial infection)

Diagnostic Testing: Equine influenza is diagnosed via nasal swabs or serum sampling and testing to detect the virus.

Treatment: Rest is the primary treatment route, however NSAIDs and antibiotics can be used if necessary to control fever, pain and inflammation.

Prognosis: Good. Recovery time for mildly affected horses is usually two to three weeks. Recovery for severely affected horses can take up to six months. Horses affected with influenza should be restricted from all strenuous activity for at least three weeks in order to allow healing of the respiratory epithelium (tissue that protects the respiratory tract). During that time, horses are extremely susceptible to development of secondary bacterial complications such as pneumonia. If horses are not given adequate rest and appropriate management, they can develop chronic reactive airway disease which can compromise their future performance.

Prevention: The primary mode of prevention is vaccination. Recommendations for initial and booster vaccinations vary depending on vaccine type; consult your veterinarian to determine what’s best for your location and situation. Horses with ongoing risk of exposure (horses that travel often or reside in high-traffic barns) should be vaccinated semi-annually. Equine influenza is highly contagious and spreads rapidly. Any horse showing signs of respiratory disease (cough, nasal discharge, persistent fever) should be isolated immediately until the cause can be determined by your veterinarian.