Tracheal microbial populations in horses with moderate asthma.
Authors: Manguin Estelle, Pépin Elizabeth, Boivin Roxane, Leclere Mathilde
Journal: Journal of veterinary internal medicine
Summary
# Tracheal Microbial Populations in Equine Moderate Asthma Whilst bacterial dysbiosis has been implicated in human asthma pathogenesis, evidence in horses remains sparse; Manguin and colleagues investigated whether airway microbiota alterations characterise equine moderate asthma by comparing tracheal aspirates from 18 asthmatic and 10 control horses using both culture and quantitative PCR to enumerate bacterial populations and correlate findings with bronchoalveolar lavage fluid cytology. Potential respiratory pathogens including Streptococcus spp., Actinobacillus spp., and Pasteurellaceae were cultured more frequently from asthmatic horses (44–67% prevalence) than controls (0–30%), yet paradoxically, total bacterial load was significantly lower in asthmatic animals (1.5 versus 2.5 × 10⁴ copy/μL, P <0.05), with no meaningful associations between bacterial populations and clinical signs, tracheal mucus production, or airway inflammation markers. Rather than supporting bacterial overgrowth as a driver of moderate asthma, these findings suggest dysbiosis may instead reflect reduced overall microbial diversity—a pattern that could result from chronic inflammatory damage, previous antimicrobial therapy, or potentially perpetuate ongoing inflammation through altered immunoregulation. For practitioners, this implies that bacterial culture positivity in asthmatic horses warrants cautious interpretation; positive isolates may represent pathological dysbiosis rather than simple infection requiring antibiotics, suggesting investigation of environmental and inflammatory management strategies as primary therapeutic targets alongside targeted microbial assessment.
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Practical Takeaways
- •Bacterial overgrowth does not appear to be a primary driver of chronic moderate asthma in horses, suggesting that antibiotic therapy targeting airway bacteria may not be first-line treatment
- •Lower bacterial loads in asthmatic horses could indicate dysbiosis from chronic inflammation or previous treatments—focus management strategies on controlling airway inflammation rather than treating presumed bacterial infection
- •Culture and qPCR results correlate reasonably well for Streptococcus spp., but consider that microbial findings alone should not guide treatment decisions without clinical correlation
Key Findings
- •Potential pathogens (Streptococcus spp., Actinobacillus spp., Pasteurellaceae) were more frequently isolated from asthmatic horses (8, 5, and 6 cases respectively) compared to controls (3, 0, and 2 cases)
- •Overall bacterial load (16S rRNA) was significantly lower in asthmatic horses (1.5±1.3 × 10⁴ copy/μL) versus controls (2.5±0.8 × 10⁴ copy/μL, P<0.05)
- •Strong positive correlation between Streptococcus spp. DNA and 16S rRNA gene detected in both groups (r≥0.7, P≤0.02)
- •No association found between microbial populations and clinical signs, tracheal mucus production, or BALF cytology inflammation markers