Tracheal wash culture is not associated with bronchial infection, remodelling or inflammation in horses with asthma.

Abstract

BACKGROUND: Antimicrobials are commonly prescribed for the treatment of equine asthma, despite limited evidence supporting their use. Tracheal wash (TW) bacterial culture results are known to influence antimicrobial prescription decisions. OBJECTIVES: To determine whether a positive TW bacterial culture in horses with asthma is associated with bronchial infection or colonisation, increased bronchial remodelling and airway inflammation by evaluating the presence of bacteria and airway remodelling in endobronchial biopsies, as well as bronchoalveolar lavage fluid (BALF) cytology and tracheal mucus scores. STUDY DESIGN: Retrospective blinded case-control study. METHODS: Tracheal wash aerobic bacterial culture, endobronchial biopsies, BALF cytology and tracheal mucus scores from horses with severe equine asthma (SEA) (n = 13), mild-to-moderate equine asthma (MEA) (n = 9) and control horses (n = 9) were evaluated. RESULTS: Tracheal wash cultures were positive in 8/13 horses with SEA, 6/9 horses with MEA and 8/9 control horses. No bacteria were identified on Gram stains in any endobronchial biopsy samples. Semiquantitative histologic scores from endobronchial biopsies did not differ significantly between asthmatic horses with positive versus negative TW cultures (p = 0.4). Neutrophil percentages in BALF were not significantly different between asthmatic horses with a positive and negative TW culture (p = 0.5). Tracheal mucus scores did not differ between asthmatic horses with positive versus negative TW cultures (p = 0.7). MAIN LIMITATIONS: Small sample size, absence of endobronchial biopsies with bacterial presence. CONCLUSIONS: A positive bacterial TW culture in horses with asthma is not associated with bronchial infection, bacterial colonisation, increased bronchial remodelling or increased airway inflammation. Therefore, a positive TW culture in these cases does not confirm the presence of a secondary bacterial infection. Tracheal wash culture results alone should not be considered a primary determinant when making treatment decisions for equine asthma.