Investigation of the Use of Environmental Samples for the Detection of EHV-1 in the Stalls of Subclinical Shedders.

Overview

• This study evaluated how well environmental samples from horse stalls can detect equine herpesvirus-1 (EHV-1) shed by horses that show no clinical symptoms.
• Researchers compared different sampling methods—nasal swabs, environmental sponges, strips above waterers, and air samples—to find which was most effective in detecting EHV-1 presence in subclinical shedders.

Background

• Equine herpesvirus-1 (EHV-1) is a respiratory pathogen affecting horses and can cause outbreaks in healthy show horse populations through subclinical transmission.
• Recent serious outbreaks of EHV-1 myeloencephalopathy (EHM), a neurological disease caused by EHV-1, have prompted stricter biosecurity protocols at horse shows, including monitoring individual horses and enhancing hygiene.
• Identifying subclinical shedders—horses shedding the virus without showing symptoms—is crucial to prevent spread, but detection can be challenging.

Study Objective

• To compare the accuracy and effectiveness of various environmental sampling techniques to detect EHV-1 in the stalls of subclinical shedders.
• To investigate if environmental sampling can serve as a non-invasive alternative or complement to direct nasal swab testing of horses.

Methodology

• Subjects: Seven healthy adult horses were used—four were vaccinated intranasally with a modified-live EHV-1 vaccine to simulate subclinical viral shedding, and three served as unvaccinated controls.
• Housing and Contact: All horses were stabled individually in the same barn; vaccinated horses had nose-to-nose contact with at least one other horse to simulate natural conditions for viral transmission.
• Sampling: Samples were collected before vaccination and daily for ten days thereafter, including:
  • 6-inch rayon-tipped nasal swabs from each horse
  • Environmental sponges swabbed inside the stall
  • Cloth strips placed above automatic waterers to collect settled virus particles
  • Air samples collected from the stalls
• Testing: All samples were processed for nucleic acid purification and tested using quantitative PCR (qPCR) to detect EHV-1 DNA.

Key Findings

• Nasal Swabs: EHV-1 was detected only briefly for 1-2 days in vaccinated horses’ nasal secretions post-vaccine, indicating short duration of detectable shedding in swabs.
• Environmental Sponges: These tested positive for EHV-1 more frequently and for a longer period (2–5 days, median 3.5 days) in vaccinated horses, with one control horse also positive for 1 day, showing environmental surfaces can retain viral material longer.
• Cloth Strips: EHV-1 was detected on strips from three of four vaccinated horses and two of three controls, but only for a single day, suggesting limited viral deposition on waterer areas.
• Air Samples: Viral DNA was detected in the air of three vaccinated horses’ stalls, but only for one day, indicating air detection may be sporadic or less sensitive.
• Overall Detection Rates in Vaccinated Horses:
  • 25% of nasal swabs were qPCR positive
  • 35% of environmental sponges were qPCR positive
  • 7.5% of cloth strips were qPCR positive
  • 7.5% of air samples were qPCR positive

Conclusions and Implications

• Environmental sponges provided the most reliable detection of EHV-1 in stalls of subclinical shedders compared to other sampling methods including direct nasal swabs.
• Environmental sampling offers a non-invasive, practical approach to monitor for subclinical virus shedding among horses without stressing the animals through repeated nasal swabbing.
• Infection control and biosecurity protocols at horse shows could incorporate environmental sampling to detect viral presence early and prevent outbreaks caused by asymptomatic carriers.
• Further studies could refine techniques and explore integration of environmental monitoring with clinical surveillance strategies to improve outbreak management.