Inflammatory phenotype and response to intradermal skin testing are not predictive of equine asthma diagnosis

The role of inflammation, allergy, and air quality in the pathogenesis of equine asthma has not yet been fully elucidated.

To evaluate serum inflammatory cytokines, intradermal skin testing (IDT), and air quality in asthmatic horses. It was hypothesized that there would be an association between environmental allergies and poor air quality with asthma.

52 client-owned horses with clinical signs consistent with asthma were enrolled in this cross-sectional study. Horses were diagnosed with asthma based on the results of bronchoalveolar fluid (BALF) cytology. Blood samples were analyzed for 23 inflammatory cytokines. IDT was conducted on a subset of 31 horses. Aerosol mass fraction concentrations were measured and converted to air quality index (AQI).

Cytologic diagnoses of asthma were made in 34/52 horses. All non-asthmatic horses that underwent IDT testing showed a severe response to ≥1 allergen (100%), while 60% of asthmatic horses showed the same response. There was a statistically significant overrepresentation of mastocytic asthma at sites with unhealthy AQI (expected 10.3%, observed 24.1%; p = 0.0213). This study failed to find any differences between asthma phenotypes for IDT results or identify inflammatory cytokines in serum as biomarkers in for allergic airway disease.

Diagnostic testing for environmental allergies and serum biomarkers were not predictive of asthma phenotypes. The association between the occurrence of equine asthma and poor air quality is consistent with results found in humans.