Equine Influenza, About
Drs. Foster & Smith Educational Staff


Equine influenza is a highly contagious viral respiratory disease. Equine influenza is caused by a virus similar to although not the same as, the type of virus that causes human flu. There are two subtypes of the influenza A virus that affects horses, H7N7 (also known as A1), and H3N8 (also known as A2).
This viral disease is spread by inhalation of drops of infective material. When an infected horse coughs or has nasal discharge, and another horse comes in contact with the infective material, that horse is exposed. The virus may also be transmitted on infected grooming tools or blankets and rugs. Most exposed horses will show signs within a period of one to five days.

Horses generally recover from an equine influenza infection within two to three weeks. Equine influenza is rarely fatal but can cause problems such as emphysema, pneumonia, or bronchitis.

Signs of equine influenza are similar to signs of other equine viral respiratory diseases, such as rhinopneumonitis. These include:

  • Dry, hacking cough,
  • Sudden onset of fever (generally over 102°F- normal temperature for a horse is 99°-101°F)
  • Watery nasal discharge
  • Coughing
  • Weakness
  • Stiffness
  • Loss of appetite
  • Depression

Equine influenza may produce more severe symptoms in horses that are sick, immune compromised, malnourished, or severely stressed.

Control of equine influenza requires sound management and proper immunization. Management includes isolating horses when they are first being introduced into a stable. Horses may be required to be vaccinated against this and other core infectious diseases prior to any showing event.