The Role of Viral Pathogens in Horse Respiratory Diseases: A Cytological and Molecular Approach Using Next-Generation Sequencing.
Authors: Mazzei Maurizio, Sorvillo Benedetta, Sgorbini Micaela, Bindi Francesca, Perelli Alice, Laus Fulvio
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Respiratory disease in horses frequently prompts investigation for infectious agents, yet conventional PCR-based diagnostics only identify known pathogens and may overlook novel or rare viruses entirely. Mazzei and colleagues employed metagenomic next-generation sequencing (NGS) on bronchoalveolar lavage fluid from 14 horses presenting with respiratory clinical signs, combining this molecular approach with conventional clinical assessment, ultrasonography, endoscopy, and cytological analysis to establish any pathogenic associations. A single positive result emerged: a 753 bp sequence with complete homology to Equid gammaherpesvirus 2 detected in a 2-year-old Thoroughbred presented for poor performance and sporadic cough during early training; notably, all other molecular analyses returned negative. The findings suggest viral involvement may be less prevalent in equine respiratory disease than suspected, though the authors appropriately acknowledge that the modest sample size limits definitive conclusions about virus prevalence in this population. For practitioners, this work serves as a reminder that whilst NGS represents a valuable tool for identifying unexpected pathogens in challenging cases, the absence of viral detection in most samples warrants continued investigation of non-infectious causes—including training intensity, environmental factors, and primary airway inflammation—when conventional diagnostics prove unrevealing.
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Practical Takeaways
- •Viral pathogens may be uncommon causes of respiratory disease in horses; consider other differential diagnoses (bacterial, fungal, inflammatory, environmental) before extensive viral screening
- •Next-generation sequencing is a useful diagnostic tool for investigating unexplained respiratory cases, but negative results do not exclude viral involvement in small populations
- •Gammaherpesvirus 2 should be considered in young horses presenting with poor performance and cough during early training phases
Key Findings
- •Only 1 of 14 horses (7%) tested positive for viral pathogens, specifically a 753 bp sequence matching Equid gammaherpesvirus 2
- •The positive case was a 2-year-old thoroughbred female presenting with poor performance and sporadic cough at training onset
- •Traditional molecular methods and next-generation sequencing revealed minimal viral involvement in this cohort of horses with respiratory disease
- •Small sample size (n=14) limits conclusions about the true prevalence of viral pathogens in equine respiratory disease