Equine Influenza is a highly contagious respiratory disease, which spreads rapidly among susceptible horses. It is rarely fatal except in young horses. The incubation period of influenza is ~1-3 days. Clinical signs begin abruptly and include high fever (up to 106 degrees F [41.1 degrees C]), serous nasal discharge, and coughing that is dry, harsh, and nonproductive. Depression, anorexia, and weakness are frequently observed. Clinical signs usually last less than three days in uncomplicated cases. Cough develops early in the course of infection and may persist for several weeks. Nasal discharge, although scant and serous initially, may become mucopurulent due to secondary bacterial infection. Mildly affected horses recover uneventfully in two to three weeks; severely affected horses may convalesce for up to six months, which is very undesirable, especially in the case of performance horses. Recovery may be hastened by complete restriction of strenuous physical activity. Respiratory tract epithelium takes ~21 days to regenerate; during this time, horses are susceptible to development of secondary bacterial complications such as pneumonia and other illnesses. Complications are minimized by restricting exercise, controlling dust, providing superior ventilation, and practicing good stable hygiene.

Clinical Signs

High fever, cough, nasal discharge, and decreased performance. 


Rest and nursing care are required. Horses should be rested one week for every day of fever with a minimum of a three-week rest. The administration of antibiotics may be necessary, especially in the case of secondary bacterial infection.

Prevention Vaccination (every three to six months), isolation of newly introduced horses for two weeks, and isolation of infected horse to reduce contamination of the healthy herd.

See Influenza in Horses for more information.