Equine influenza, often simply referred to as “horse flu,” is a highly contagious respiratory disease caused by the equine influenza virus (EIV). It affects horses, ponies, and other equids worldwide, leading to significant economic losses and impacting equine health and welfare. Equine influenza is characterized by fever, coughing, nasal discharge, and respiratory distress, and it can spread rapidly through populations of susceptible horses, particularly in environments where horses are in close proximity, such as stables, training facilities, and equestrian events.

Equine influenza spreads primarily through the inhalation of respiratory secretions from infected horses. It can also be transmitted indirectly through contact with contaminated equipment, clothing, or surfaces. Horses shed the virus for several days after infection, even before showing clinical signs, facilitating the rapid spread of the disease within a population.

The clinical signs of equine influenza typically appear suddenly and include fever (often 102°F), nasal discharge (usually clear and watery initially, becoming thicker and mucopurulent as the disease progresses), dry and hacking cough, lethargy, anorexia, and respiratory distress, especially during exercise. Affected horses may exhibit varying degrees of illness, from mild respiratory symptoms to more severe pneumonia.

While most cases of equine influenza resolve within 2-3 weeks with supportive care, complications such as secondary bacterial infections (pneumonia) or exacerbation of underlying respiratory conditions can occur, particularly in young, old, or immunocompromised horses. These complications can prolong recovery time and increase the risk of long-term respiratory issues.

Diagnosis of equine influenza is based on clinical signs, history of exposure to infected horses, and laboratory testing, such as polymerase chain reaction (PCR) or virus isolation from nasal swabs or respiratory secretions. Serological testing to detect antibodies to the influenza virus may also be performed to confirm exposure or immunity.

Treatment of equine influenza is primarily supportive and aimed at managing clinical signs and preventing secondary complications. This may include rest, isolation to prevent the spread of infection, anti-inflammatory medications to reduce fever and inflammation, bronchodilators to alleviate respiratory distress, and antibiotics if secondary bacterial infections are suspected.

Prevention of equine influenza relies on vaccination and strict biosecurity measures. Vaccination against equine influenza is available and recommended for all horses, particularly those at high risk of exposure, such as horses traveling to shows, competitions, or racing events. However, vaccination does not provide complete immunity and may require regular boosters to maintain protection. Biosecurity measures, such as quarantine of new arrivals, isolation of sick horses, and disinfection of equipment and facilities, are essential for preventing the introduction and spread of equine influenza within equine populations.

Equine influenza outbreaks can have significant consequences for the equine industry, including disruptions to competitions, racing events, and horse trading. Timely recognition, prompt implementation of control measures, and adherence to vaccination and biosecurity protocols are crucial for mitigating the impact of equine influenza and maintaining the health and welfare of horses.