Airborne detection of Equid alphaherpesvirus 1 at international equestrian events.

Overview

• This study investigates the presence of Equid alphaherpesvirus 1 (EHV-1) and Equid alphaherpesvirus 4 (EHV-4) in air and on surfaces at international horse events to assess if air sampling could be a useful, non-invasive surveillance method for viral detection.

Background

• EHV-1 is a significant pathogen affecting horses worldwide, causing respiratory illness, neurological disease, and abortions.
• Recent outbreaks at international equestrian events have highlighted the need for better detection and monitoring methods to prevent virus spread.
• Traditional surveillance often relies on individual horse testing, which can be resource-intensive and invasive.

Objectives

• Determine if EHV-1 and EHV-4 viral DNA can be detected in the shared airspace and on surfaces in contact with horses during international equestrian events.
• Evaluate whether air sampling is a feasible alternative surveillance technique compared to testing individual horses.

Methods

• A cross-sectional field study was conducted over 10 months during 8 international equestrian events (6 in Spain, 2 in the USA).
• Samples were collected from temporary stabling facilities: 37 air samples and 205 surface swabs.
• Sampling took place at different seasons and included two time points during Spanish events—early evening and night—to compare viral loads during high and low horse activity periods.
• Viral DNA was quantified using quantitative PCR and digital PCR techniques.

Key Findings

• EHV-1 Detection:
  • Airborne EHV-1 was frequently detected: 20 out of 28 samples in Spain, all 3 in Florida, and 3 out of 6 in Kentucky.
  • Surface samples positive for EHV-1 were 15.6% in Spain, 26.3% in Florida, and none in Kentucky.
• EHV-4 Detection:
  • Airborne EHV-4 was found in 12/28 Spanish samples, 5/6 Kentucky samples, but none in Florida.
  • Surface detection rates for EHV-4 were lower: 1.6% in Spain and 7% in Kentucky.
• Daytime versus Nighttime Viral Loads:
  • No significant difference was found between air viral loads during high activity (daytime) and low activity (nighttime) periods.
  • This suggests horse movement and management practices during the day did not notably influence airborne viral presence in this study.
• Correlation of Air and Surface Samples:
  • There was a positive correlation (Cohen’s K = 0.401) between surface and air sample positivity for EHV-1.
  • This moderate agreement points to air sampling as a practical, non-invasive method for cohort-based surveillance of EHV-1.

Limitations

• The study used only molecular detection methods (PCR), which identify viral genetic material but do not confirm the presence of infectious virus particles.
• Without virus isolation or culture, it is unclear whether detected viral DNA corresponds to active infection or transmission risk.
• Sampling was limited to specific events and times, possibly affecting generalizability.

Conclusions and Implications

• Air sampling effectively detected EHV-1 presence in mass gatherings of horses, suggesting it could be an early warning surveillance tool.
• The non-invasive nature of air sampling makes it attractive for screening large groups without stressing individual animals.
• Further research is needed to:
  • Validate the relationship between detected viral DNA and actual infectious virus shedding.
  • Establish direct links between air sampling results and transmission events.