Equine flu & what to look out for

Equine influenza, or horse flu, is an infectious disease that affects a horse’s respiratory system with symptoms usually appearing within 1 to 3 days of infection. It’s a viral disease that will spread quickly through a group of horses.

It’s not believed to be a seasonal illness but the mixing of horses at events can contribute to outbreaks at certain times of the year.

What causes equine influenza?

It is caused by a virus and horses are routinely vaccinated against it.

As it’s an airborne virus it will spread quite quickly among a herd of unvaccinated horses, with some horses being a carrier of the illness while appearing healthy and not showing any symptoms.

An indirect spread is also possible, especially when sharing feed buckets or through handlers and vets that have previously been around an infected horse.


Vaccinating a horse against equine influenza can prevent the horse from falling ill and these should be repeated annually. Sometimes, though, as appears to have happened here the current vaccines haven’t completely immunised against this strain.

Despite this, keeping up to date with annual boosters can provide a level of protection against the worst symptoms.

Vaccination is compulsory when competing under British Horseracing Authority, FEI and affiliated governing bodies, like the British Equestrian Federation.

Equine influenza symptoms

  • A very high temperature of 39-41C (103-106F) which lasts for one to three days.
  • Rapid breathing as well as a frequent dry deep cough that can last for several weeks.
  • Clear, watery discharge from the eyes and nasal discharge that may become thick and yellow or green.
  • Enlarged lymph nodes that would result in a sore throat.
  • Clear discharge from the eyes and redness around eyes.
  • Lethargic, loss of appetite and possible anorexia.
  • Swelling of the lower limbs as well as possible muscle pain.

If your horse is showing any of these signs, please contact your vet immediately.

Horses should be vaccinated against equine influeza

Equine influenza diagnosis methods

A diagnosis can usually be made on the symptoms alone, but they do share some symptoms with other respiratory viral infections which won’t make a difference to the treatment.

Otherwise, an accurate diagnosis of the virus can be made by:

  • Nasal or nasopharyngeal swabs.
  • Taking blood samples and looking at the antibody levels.
  • Looking at the history of recent contact with a confirmed case of the disease.

Equine influenza treatment

There is no treatment to kill the virus, but the management of the virus is key to a horse’s quick recovery.


A horse infected by influenza should be rested for at least six weeks. This recommended time will allow any damaged tissues from the illness to fully heal.

Bedding and cleanliness

It’s important that an infected horse can be stabled in clean and well-ventilated areas so you might want to consider switching to dust-free bedding for the time being. This will avoid any further irritation to the horse’s respiratory system.


Feeding the affected horse soft feed, wet hay, or haylage is recommended while they recover, and these should be served from the floor.


Antibiotics have no effect against the virus but will be used if the horse has contracted a secondary infection due to the flu. For example, if the horse suddenly contracts pneumonia the veterinarian will then prescribe some antibiotics.

Recovery of influenza in horses

Horses should make a full recovery from equine influenza, but occasionally complications can occur, especially if a secondary infection was found.

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