An article in the Journal of Comparative Pathology described an outbreak involving a particularly severe influenza strain in England. Two infected horses developed neurological signs, one of which was euthanized. Postmortem studies showed influenza virus present in the nasal mucosa, and the brain showed changes typical of a viral encephalitis. Although these findings didn’t prove the brain was also infected by influenza virus, the authors pointed out this can happen in other species.
While not every horse needs influenza vaccine, horses at high risk should be vaccinated to help decrease the severity of the disease. The virus causes high fevers, extreme weakness and leaves the horse susceptible to secondary lung infections. Skeletal muscle pain and even involvement of the heart muscle may occur.
Horses with flu should have protection from chills and stress, and be fed high-quality feeds, including moist meals, to encourage them to eat. They shouldn’t be worked until completely recovered and hard work avoided for an additional 10 to 14 days.