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Equine Influenza

​February 2020 

Equine Influenza, also referred to as equine flu, is a highly contagious viral respiratory disease. When an infected horse coughs or sneezes droplets are released into the air which can spread the virus via an airborne route. Equine flu can also spread via direct contact from horse to horse or indirectly for example, by handlers, equipment and feed buckets. The incubation period for the disease is between one to five days. Therefore, an influenza outbreak can quickly spread between horses.

Clinical Signs

  • An increased temperature for one to three days of up to 41°C (106°F). This can happen before any visible signs are shown by the horse. If you’re not sure how to take your horse’s temperature, please watch our video below.
  • The horse’s airway will become swollen and sore. This results in the onset of a dry, harsh cough, which can continue for two to three weeks and potentially continue for up to six weeks after all other clinical signs have subsided
  • A clear, watery nasal discharge that may become thick and yellow or green in colour, a few days later
  • Loss of appetite
  • The horse is lethargic
  • Swollen and painful glands under and around the jaw.

The disease can weaken a horse, leaving it vulnerable to secondary infections including bronchitis, pneumonia, swelling of the lower limbs and sore muscles. Such complications are particularly worrying in young foals, elderly animals and those with a pre-existing respiratory disorder and in serious cases this could cause death.

Treatment and Management

If flu is suspected, isolate your horse and contact your vet. It is likely that a swab will be taken and possibly a blood test.

  • There is no direct treatment for flu, much like people with flu, the best treatment we can provide is supportive care and plenty of rest
  • The horse’s environment should be isolated to prevent further spread of the virus and kept as dust free as possible, to ensure the respiratory system is not compromised further
  • It can take several weeks for the horse to recover and return to full health. In compromised horses the risk period of secondary complications such as pneumonia, can last between 50-100 days post-infection. It is important to seek your vet’s advice before returning your horse to work to ensure the horse isn’t over stressed or over worked.

Decreasing the Risk

Vaccination remains the most important practice in decreasing the risk of flu. The vaccination programme begins with a series of injections administered over the first year, which is then continued by boosters to maintain cover against the virus. It is important not to allow the booster to lapse because even being one day late will result in the initial vaccination programme having to be restarted, which will be costly for the owner.

Upon the vet’s arrival to vaccinate the horse ensure the horse’s passport is available so the injection can be correctly recorded. If you have any concerns that your horse might not be well for example, they are lethargic or not eating as usual, speak to your vet ahead of vaccination. It may be that your horse is incubating a disease and therefore vaccinating at this point could produce a negative reaction.

Vet Checking Passport

Photo credit: The Royal Veterinary College

Flu is an adaptive virus and can change over time; this is a process known as antigenic drift. As a result, although vaccines are available, it can be difficult to keep them fully up to date with the most current strain. This means the vaccines may fail to provide full immunity against the most recent strain. Therefore, there have been cases where vaccinated horses can suffer with flu. However, vaccinated horses will not be as severely affected and will suffer with the disease for less time compared to unvaccinated horses. Your vet will be best to advise on the most current vaccine available.

Horse Vaccination

Maintaining good health and hygiene management practices on your yard, with the correct disease prevention measures in place, can also help to prevent the spread of equine flu. Read our advice and the simple steps you can take to prevent the spread of disease.

Herd Immunity

Where a higher percentage of the equine population is vaccinated, the spread of the disease is ultimately reduced. However, for herd immunity to work a large proportion of the population must be vaccinated. Estimates suggest that only 50 percent of the equine population in the UK are vaccinated against influenza. Through following the advised vaccination procedure, you are not only protecting your own horse, but also increasing the UK’s herd immunity. All horses are at risk of flu as in certain weather conditions it can travel up to several kilometres.

Shows and Events

The horse’s passport should also be taken to all shows and events as vaccination checks may take place. It is essential to check with the show organisers or relevant governing body on their specific vaccination requirements. If your horse does not meet their requirements it is likely that you will not be allowed to compete. If you hire equestrian facilities it is important to check the vaccination rules of the venue.


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