Airborne detection of Equid alphaherpesvirus 1 at international equestrian events.

Background: Equid alphaherpesvirus 1 (EHV-1) remains a major concern for the equine industry, with recent outbreaks at international equestrian events highlighting the need for improved surveillance during competitions.

Objectives: To investigate EHV-1 and -4 presence in shared airspaces and environmental surfaces in direct contact with horses at international equestrian events; and to evaluate air sampling as a surveillance alternative to individual horse testing.

Study design: Cross-sectional field study.

Methods: Air (37) and surface samples (205) were collected from temporary stabling facilities across six events in Spain and 2 in the United States at different seasons over 10 months. Viral DNA (genomic copies) was measured and quantified by quantitative and digital PCR. During all the Spanish events, we sampled the air twice, early evening and night.

Results: EHV-1 was frequently detected in the air in 20/28 samples in Spain, in all 3 samples from Florida and in 3/6 samples from Kentucky. Surface samples were positive 15.6% in Spain, 26.3% in Florida and 0.0% in Kentucky. EHV-4 was found in air samples at rates of 12/28 in Spain, 5/6 in Kentucky and 0/3 in Florida, with surface detection of 1.6% in Spain and 7% in Kentucky. No significant differences were observed between daytime (high activity) and nighttime (low activity) airborne viral loads, suggesting that daytime horse movement and management practices had minimal impact on detection levels in our study. A positive correlation (Cohen's K = 0.401) and moderate agreement between surface and air positivity for EHV-1 emphasised the potential of air sampling as a non-invasive, cohort-based surveillance tool.

Main limitations: Virus isolation was not used; only molecular detection was employed, which limits conclusions about transmission risk.

Conclusions: These findings underscore the utility of air sampling for early EHV-1 detection at mass gatherings; although further validation is needed to connect genomic detection to active shedding and viral infectivity.