Equine Asthma Diagnostics: Review of Influencing Factors and Difficulties in Diagnosing Subclinical Disease

This literature review focusses on diagnostics of Equine Asthma (EA), possible influencing factors on diagnostic techniques and latest developments in diagnosing horses during EA remission or in case of subclinical disease. Routine EA diagnostics include clinical examination of the respiratory system including percussion and auscultation, clinical pathology including white blood cells and arterial blood gas analysis, bronchoscopy to evaluate the amount and viscosity of respiratory secretion, bronchoalveolar lavage and cytology of tracheal aspirates (TA) and bronchoalveolar lavage fluid (BALF). Grading of EA severity and inflammatory subtype is based on BALF cy-tology, while TA cytology helps to rule out previous bacterial infections. Different factors have an impact on the airways regarding structure of the epithelium, cytology and inflammatory markers possibly influencing the diagnosis of EA. Short-term exercise increases the total cell count and inflammatory mediators in BALF of men, asymptomatic horses and other species. Further factors involve cold or chlorinated air, long-term training effects and the co-incidence of further respir-atory disease, in particular exercise-induced pulmonary hemorrhage. As BALF cytology may be unremarkable during EA remission and low-grade disease, exercise and other factors stressing the bronchial epithelium may help to diagnose these patients.