Equine influenza

Equine influenza (Horse flu) refers to varieties of Influenzavirus A that are endemic in horses. Horse flu viruses were only isolated in 1956. There are two main types of virus called equine-1 (H7N7) which commonly affects horse heart muscle and equine-2 (H3N8) which is usually more severe. Horse flu is endemic throughout the world.

The disease has a nearly 100% infection rate in an unvaccinated horse population that has not been previously exposed to the virus. The incubation time is one to five days.

Horses with horse flu can run a fever, have a dry hacking cough, have a runny nose, and become depressed and reluctant to eat or drink for several days but usually recover in 2 to 3 weeks.

"Vaccination schedules generally require a primary course of 2 doses, 3-6 weeks apart, followed by boosters at 6-12 month intervals. It is generally recognised that in many cases such schedules may not maintain protective levels of antibody and more frequent administration is advised in high-risk situations."

It is a common requirement at shows in Britain that horses are vaccinated against Equine flu and a vaccination card must be produced; the FEI requires vaccination every 6 months.

In August 2007, a notable outbreak occurred in Australia which had previously been free of the virus.