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Equine influenza is a contagious viral respiratory disease that can affect all equines including horses, donkeys, mules, and zebras. Signs of infection may include high fever, a dry cough, discharge from the eyes and nose, loss of appetite, and depression. Some horses develop swollen lymph nodes under the jaw; other horses may show swelling and stiffness in their legs. The disease is spread between horses by contact with nasal discharge, and infected horses can spread the disease to other equines for seven to fourteen days.

Any horse can develop equine influenza, though very young foals and senior horses are somewhat more susceptible. While it is rarely fatal, influenza can cause significant illness and usually requires the horse to be out of training or work for several months. Diagnosis is often made from exposure history and clinical signs, and blood tests and nasal swabs can confirm the diagnosis.

Treatment steps include rest and supportive measures. Infected horses should be taken out of work to avoid damage to a compromised respiratory tract. If they are stalled, managers should be careful to provide fresh air and a dust-free environment. Total stall rest is not necessary, and horses can be kept outside in good weather if shelter is available. Stalled horses should be walked in-hand for brief periods to avoid boredom and stocking up.

To avoid spreading the disease, infected horses should be cared for after healthy horses are handled. Sick animals should be isolated, and handlers should disinfect their clothing, boots, hands, and equipment after caring for sick horses. The equine influenza virus can live up to two days on hard surfaces such as buckets or stall surfaces, but it is easily killed with soap and water or disinfectant solutions. It is also killed by exposure to sunlight, so outdoor surfaces are self-cleaning to some extent.

After the horse’s temperature returns to normal and the cough abates, the horse may still need up to a month of rest. This break in work allows the tissues of the respiratory system to heal. Resuming training too quickly can increase the risk of a serious secondary bacterial infection such as pneumonia. When the horse is put back into training, the rider should allow another month of gradually increasing exercise before asking for strenuous performance.

Equines can be vaccinated against equine influenza, but full protection may last for only a few months. Horses that never leave the farm are usually vaccinated once a year. Those that are at increased risk for influenza exposure, such as horses that travel or show frequently and are in contact with other horses, should be vaccinated more often for complete protection. Even with frequent vaccination, it is possible for horses to become ill with influenza, but they will rarely develop a severe infection.

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