Equine Influenza

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Equine influenza is a major disease caused by a virus. Present in North America, Europe, Australia, and parts of Asia, equine influenza produces severe symptoms, including fever, a dry hacking cough, nasal and eye discharge, swollen lymph nodes under the jaw, depression, lethargy, and loss of appetite.

Blood tests and nasal swabs are necessary for a definite diagnosis. Most horses recover within one to two weeks, but the dry cough may last much longer.

Vaccines are available, and if an effective schedule of vaccinations and booster shots is followed, a horse's immune status may be ensured. In some cases, horses that have been vaccinated may become infected, but usually their symptoms and the duration of the disease will be much less severe.


  • High temperature lasting for one to five days
  • Dry, harsh sounding cough
  • Nasal discharge that may turn green or yellow as secondary infections develop
  • Depression
  • Lethargy
  • Loss of appetite
  • Muscle soreness
  • Enlarged lymph nodes
  • Colic
  • Swellings in legs and scrotum


Equine influenza is caused by a type-A Orthomyxovirus. Two major strains are known to cause the disease. These viruses are from the same group of viruses that causes flu in humans. The disease has a nearly 100% infection rate in unvaccinated horses and has a relatively short incubation period of one to three days.


A regular vaccination schedule with a primary course of two doses, 3-6 weeks apart, followed by boosters at 6-12 month intervals, is generally suggested. In many cases, such schedules may not maintain protective levels of the antibodies, and more frequent administration is advised in high risk situations where horses might be in contact with horses that have not been immunized.


Because equine influenza is caused by a virus, no drugs have been developed to successfully treat the disease. In addition, many horses develop secondary infections from bacteria that can lead to pneumonia and other problems.

A horse with influenza should be isolated from other horses. Treatment is largely supportive, with good nutrition and proper care helping to create an effective immune response. Rest and Butazolidin, to control fever and muscle stiffness, will help keep the horse more comfortable.

The stall should be dry and well-ventilated. If the stable is cold, provide a warm horse blanket, along with clean water and a palatable diet. Exercise should be curtailed and the horse rested for at least three weeks to prevent relapse and development of chronic bronchitis.

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.