Inflammatory Airway Disease in Horses

Inflammatory airway disease is a group of inflammatory conditions of the lower respiratory tract that do not appear to be caused by disease organisms. Inflammatory airway disease occurs in up to 50% of athletic horses, and it is a common cause of impaired performance and interruption of training.

Factors that may be involved in the development of inflammatory airway disease include allergic airway disease, recurrent lung stress, deep inhalation of dust, pollutants in the air, and persistent respiratory viral infections. Inflammatory airway disease often develops following a viral respiratory infection, and may result from an inability of the immune system to fully eliminate viruses or bacteria from small airways. The bacterium Streptococcus pneumoniae has been isolated from young horses (less than 2 years of age) with inflammatory airway disease. Its role in the disease is unclear because inflammatory airway disease does not respond to antibiotic therapy.

The most common signs are a chronic cough, nasal discharge, and poor tolerance for strenuous exercise. Affected horses appear normal at rest; fever and abnormal lung sounds are rare. Endoscopic examination reveals mucous and pus in the upper throat, windpipe, and lungs. A diagnosis of inflammatory airway disease is often based on poor race performance and signs. Microscopic examination of fluid from the lungs can help determine whether infection or inflammation are involved and can help determine appropriate therapy. Signs may be similar to those of recurrent airway obstruction, another inflammatory condition your veterinarian may need to rule out.

Horses with inflammatory airway disease (regardless of the specific type) typically are prescribed aerosolized bronchodilator medication for use prior to exercise in order to prevent exercise- or irritant-induced airway constriction. In addition, drugs such as antiviral medication or corticosteroids (for relief of inflammation) may be prescribed.