Effects of nebulized dexamethasone on the respiratory microbiota and mycobiota and relative equine herpesvirus-1, 2, 4, 5 in an equine model of asthma.
Authors: Bond Stephanie L, Workentine Matthew, Hundt Jana, Gilkerson James R, Léguillette Renaud
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Corticosteroids remain a cornerstone of asthma management in horses, yet their effects on the respiratory microecosystem—particularly viral latency and microbial communities—are poorly understood. Researchers compared 16 horses with naturally occurring mild asthma and 4 healthy controls using molecular sequencing of 16S and ITS2 genes from nasal swabs and tracheal aspirates, quantifying equine herpesvirus expression before and after 13 days of nebulized dexamethasone (15 mg daily) or saline control. Dexamethasone treatment reduced overall microbial diversity and altered the relative abundance of eight bacterial genera in the upper airway, whilst paradoxically increasing Alternaria—an opportunistic fungal pathogen associated with asthma severity and exacerbations in humans—and shifting the balance of gamma herpesviruses by elevating EHV-2 DNA whilst suppressing EHV-5. Environmental factors (dusty stable conditions) proved far more influential on fungal communities than steroid treatment itself, leaving mycobiota composition largely unchanged. These findings suggest that whilst nebulized corticosteroids effectively reduce airway inflammation, they may inadvertently favour colonisation by problematic opportunistic organisms; this warrants consideration when designing long-term asthma protocols, particularly in poorly ventilated environments where environmental control measures deserve equal emphasis to pharmacological intervention.
Read the full abstract on PubMed
Practical Takeaways
- •Nebulized dexamethasone reduces microbial diversity in asthmatic horses but may increase opportunistic fungal pathogens like Alternaria; monitor respiratory health after treatment
- •Dexamethasone treatment alters herpesvirus gene expression (increased EHV-2, decreased EHV-5); consider implications for latent viral reactivation in treated horses
- •Environmental management (reducing dust exposure) may be as important as or more important than corticosteroid treatment in controlling respiratory microbiota changes in asthmatic horses
Key Findings
- •Nebulized dexamethasone (15 mg q24h for 13 days) decreased respiratory microbial diversity and altered relative abundance of 8 genera in the upper respiratory tract
- •EHV-2 DNA levels increased while EHV-5 DNA levels decreased following dexamethasone treatment
- •Alternaria, an opportunistic pathogen and asthma risk factor, increased with dexamethasone treatment
- •Environmental factors (dusty conditions) had a dominant effect over treatment on mycobiota composition