Clinical Signs

The signs of equine influenza usually start suddenly, with an affected horse abruptly developing a high fever. A dry, harsh cough begins early in the infection and may last for weeks. The nasal discharge initially is watery and scant, but usually becomes yellow and heavy, due to secondary bacterial infection. A sick horse may have watery eyes, enlarged lymph nodes between the mandibles, edema and stiffness in the legs, and breathing difficulty. Depression, weakness, and loss of appetite are common. Horses with relatively mild cases of equine influenza usually recover in a week or so, but severely ill horses may require weeks to months to recover fully, especially if they are not allowed to rest completely. Most uncomplicated cases recover fully, but affected animals under stress, or ones not allowed to rest, may develop secondary pneumonia, a chronic cough, or inflammation of the heart muscle, sometimes resulting in death.

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