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United Kingdom

Equine Influenza

Horse with runny nose


Equine influenza (EI) virus or ‘Equine Flu’ is a highly contagious viral pathogen causing respiratory disease and is considered endemic in Europe and North America. Outbreaks of disease occur most often when susceptible horses are congregated and housed in close contact with each other eg: horse show, sales and racetracks therefore equine influenza is major source of disruption of equestrian activities.

Like human ‘flu’, the virus is constantly evolving resulting in various different ‘strains’ causing disease outbreaks. Strains are named after the location and the year in which they were first discovered, e.g. South Africa 03, and they are monitored closely to help us in prevention and control.

The disease is spread directly from horse to horse as airborne virus particles in the environment, or via contamination of clothing or equipment. It is so contagious that in a susceptible group of horses up to 100% may become infected. As the virus is airborne, infected horses shed the virus into the air, eg, when they cough. Other horses in the vicinity then inhale the virus and then become infected.

The incubation period for equine ‘flu’ is typically only 48 hours and horses can remain infectious for approximately a week after the onset of clinical signs. The symptoms of equine ‘flu’ include increase in temperature, loss of appetite, lethargy, snotty or runny nose, swollen neck glands and cough. In general, uncomplicated cases of influenza resolve within 1 – 2 weeks, although the cough may persist for several weeks after infection. Complications of equine influenza can be severe and include secondary bacterial pneumonia, muscle soreness, inflammation of the heart muscle and limb swelling.



1. Landolt G.A (2014) Equine influenza. Vet Clin Equine 30, 507-502
2. Paillot R (2014) A systematic review of recent advances in Equine Influenza vaccination. Vaccines , 797-831;