Mechanisms of equine recurrent airway obstruction: changes in understanding and management

Abstract

Recurrent airway obstruction (RAO) is an inflammatory and obstructive disease that is more prevalent in horses stabled for long periods. The most common clinical signs include cough, exercise intolerance, dyspnea, nasal secretion and absence of fever. The pathophysiological effects of RAO in the lungs include goblet cell metaplasia, alveolar fibrosis, neovascularization, airway wall thickening affecting all tissue layers, and bronchial smooth muscle hypertrophy. The alveolar macrophage is the main effector of particle elimination in the inflammatory process of RAO, with the ability to increase or suppress inflammatory responses. Activation of macrophages increases the release of cytokines that enhance the inflammatory reaction, such as interleukin-1, tumor necrosis factor alpha, and interleukin-8, resulting in the attraction of neutrophils to the alveolar environment, which becomes the predominant cell type during periods of crisis. Although the clinical signs of RAO are well-defined, the underlying immunologic mechanisms are still being investigated. This review provides information about this disease, the understanding of which has changedover time.