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Equine Influenza – ‘Flu’

Horses are susceptible to a number of serious infectious diseases, eg influenza (flu) and tetanus (lockjaw). Fortunately there are vaccines available for some of these common conditions.

Equine influenza is a highly contagious viral disease that affects the upper and lower respiratory tract of the horse caused by different strains of influenza virus. A horse contracts the virus either through contact with an infected horse or indirectly by contaminated environments/air. Infected horses incubate the disease for 1-3 days before displaying any symptoms, which is why outbreaks of equine influenza spread so rapidly.

The disease is endemic now, but it tends to mutate to new strains which, once developed abroad, if introduced to this country act as epidemic infections. Foreign strains of the disease can cause local to national outbreaks. There are, however, vaccines that are kept up-to-date for regular use to protect horses from the disease.

Symptoms include:

  • A rise in temperature up to 41°C (106°F) for 1-3 days (often undetected)
  • A harsh, dry cough of sudden onset that persists for 2-3 weeks or more
  • Clear nasal discharge progressing to thick, green-yellow discharge
  • Lethargy/depression
  • Loss of appetite

Approved vaccination schedules for the influenza vaccine are published by the Jockey Club, International Equestrian Federation (FEI) and various show societies and committees and these form part of the entry requirements for horses competing or racing in their events. Unfortunately, these schedules differ between organisations and it is confusing for the owner to determine which they should follow. To complicate matters further, the manufacturers’ of each vaccine recommend a different schedule again, based on the efficiency of their vaccines determined by clinical trials.

The manufacturers’ recommendations provide your horse with the most protection against influenza and will satisfy Jockey Club, FEI, most racecourse and show committee regulations.

Vaccination is essential and very effective. The most common manufacturer’s vaccination schedule for equine influenza is:

  • Primary course – 2 injections, 28-42 days apart
  • First booster – 182 days (6 months) after 2nd primary injection
  • Following boosters – annually, within 365 days of preceding booster. However, if in a high risk group, i.e. competing, showing, etc or during an outbreak, a booster should be given every 6 months

If you observe any signs of equine influenza then make sure you do the following:

  • Call the vet immediately
  • Stable your horse
  • Do not exercise

Equine influenza in most adult horses causes tracheobronchitis which is fairly easy to control and treat. Your horse is likely to recover in a relatively short period of time, usually within 1-3 weeks, if the problem is diagnosed early on. In young foals, animals that are stressed in other ways or where secondary bacterial infection of the lower respiratory tract occurs, then there may be additional complications of pneumonia or damage to the heart muscle (myocarditis).

  • Isolate any new arrival into a stable yard for 3 weeks
  • Maintain good ventilation and dust-free regimens in stables
  • Make sure all horses in a stable yard, including your own, are correctly vaccinated.