A virus called equine influenza A2 virus (EIV) causes flu in horses. Horses contract EIV when they interact with other infected equids. The A2 EIV is also called subtype H3N8 (which, to scientists, relates it to the H3 flu viruses in other animals). The EIV A1 subtype is considered extinct.

Horses often become infected at shows or other events where groups horses commingle or when introduced to new horses to an established facility. Young horses (ages 1 to 5) with limited natural immunity, unvaccinated equids, and those that come into frequent contact with large numbers of horses have the highest infection risk.

Download this free fact sheet to learn how to protect your horse from influenza, a highly contagious respiratory disease.