Equine Influenza: Signs, Transmission and Treatment

What is Equine Influenza?

Equine influenza (EI) is a highly contagious viral disease which can cause rapidly spreading outbreaks of respiratory disease in horses and other equine species. Very young and very old animals are the most susceptible to infection, clinical signs and complicating secondary bacterial infections.

Equine Influenza in Australia

Equine Influenza is exotic to Australia, however an outbreak in New South Wales in 2007 (from an imported horse) affected thousands of horses. This outbreak was eradicated within six months and Equine influenza has not been detected in Australia since.

If it were to become established, it would have a major impact on the horse industry.

Transmission of Equine Influenza


EI is rapidly spread between close contact in horses via inhalation of respiratory droplets. Infected horses excrete the virus in their nose and mouth for up to 14 days after initial infection. Coughing increases the rate of spread.

People, clothing and equipment

Infection can also be spread via clothing, horse equipment, people, buildings that have recently housed sick horses, vehicles, floats, grooming and veterinary instruments.

Can humans get Equine Influenza?

Humans do not get infected with EI, however, can physically carry the virus on their skin, hair, clothing and shoes, and can therefore transfer the virus to other horses. It is vital that you shower and wash thoroughly and put on a completely fresh set of clothes (including shoes) after contact with any horses that might be infected with EI.

Clinical signs of Equine Influenza

The main clinical signs are:

  • sudden increase in temperature (to between 39 and 41°C)
  • deep, dry, hacking cough
  • watery nasal discharge which may later become thick and smelly.

Other signs can include depression, loss of appetite, laboured breathing, muscle pain and stiffness.

The clinical outcome after viral exposure largely depends on the animals’ immune status. An immunocompromised animal will be more effected

Severity and duration of symptoms

Clinical disease varies from a mild, inapparent infection to severe disease in susceptible animals. Influenza is rarely fatal except in donkeys, zebras, and debilitated (immune compromised) horses.

Clinical signs usually last between 3 days to 3 weeks however severely affected horses may take as long as 6 months to recover.


Affected horses are susceptible to the development of secondary bacterial infection such as pneumonia, pleuropneumonia, and chronic bronchitis. While EI is rarely fatal, these complications can cause long-term debility and sometimes death, especially in foals.

Treatment of Equine Influenza


Horses that do not develop secondary bacterial infections simply require rest and supportive care.

Animals should be rested 1 week for every day of fever, with a minimum of 3 weeks rest. This will reduce the likelihood of complicating secondary infection.


Anti-inflammatories are recommended for horses with a fever greater than 40°C. Antibiotics are indicated when fever persists beyond 3–4 days or when purulent nasal discharge or pneumonia is present.


Anything that comes into contact with an infected horse should be carefully and thoroughly cleaned and disinfected including handlers and their clothes and shoes.

Prevention of Equine Influenza

Prevention of EI is largely based on hygienic management practices. The virus survives in the environment for up to 36 hours, but is easily killed by thorough cleaning and disinfection. Clean all surfaces with a powerful alkaline detergent to remove organic matter then disinfect with a high quality disinfectant that is efficacious against the Equine influenza virus.

Equine Influenza vaccine

Vaccines are available to help prevent equine influenza, but they are considered aids and not preventative in their own right. The key to prevention is a strict stable and farm hygiene program.

Zamira is an Australian animal health company with a mission to improve the health, wellbeing and productivity of animals across the world. Read more about us here.

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