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By: Dr. Lydia Gray, SmartPak Medical Director/Staff Veterinarian
Updated on: 7/31/2019
Equine Influenza (“horse flu”), is a highly contagious infection of the respiratory tract of horses. Caused by a virus, the signs and symptoms of this disease are not specific just to influenza. Therefore, it is important to have a veterinarian examine and diagnose any horse with a fever, nasal discharge, and coughing so that appropriate treatment can be given. As with other diseases in horses, “prevention is the best medicine,” with vaccination, quarantine, and isolation the best methods to keep equine influenza from spreading to other horses.
Once infected with the influenza virus, it does not take long for a horse to show signs of illness. The incubation period for “horse flu” can be as short as 24 hours, although it typically takes 3 to 5 days for clinical signs to appear. The signs of equine influenza resemble those of other respiratory diseases in horses such as “strangles” EHV or Equine Herpesvirus, and others, and include:
As with any disease or condition, a diagnosis is made by a veterinarian based on the horse’s history, clinical signs, and whether other causes can be ruled out by testing. In the case of equine influenza, recent technological advances in testing have made it possible to rule in this disease.Vets now have several reliable methods of determining with confidence if the underlying cause of a horse’s respiratory signs are caused by the equine influenza virus. From virus isolation and real-time PCR (polymerase chain reaction) of nasopharyngeal swabs to immunoassays that recognize antigens and antibodies, to traditional blood titers taken two weeks apart, some tests can even be performed “stall-side” or immediately at the farm.
There is no specific treatment for “flu” in horses as it is caused by a virus. After isolating sick horses, general supportive care (rest, NSAIDs, palatable food) of sick horses along with good stable hygiene (fresh, clean air and bedding) may be all that is needed unless fever persists, nasal discharge becomes thick and yellow, or the horse becomes more ill. In these cases, a secondary bacterial infection may have developed requiring the use of antibiotics. Equine influenza that is not complicated by pneumonia, bronchitis, or other issues typically runs its course in 2 to 3 weeks, although more serious cases can take as long as 6 months to fully recover. Because exercise while the respiratory lining is healing can delay recovery and even lead to long-term breathing and performance problems, the rule of thumb is one week of rest for every day of fever, and no exercise for any horse with a cough.
SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.
Article First Published July 31, 2019