Intermittent shedding dynamics of EHV-1 across biological matrices during a natural outbreak linked to international equestrian events.

Research Article Overview

• This study investigated how equine herpesvirus type 1 (EHV-1) is shed over time in different biological samples from naturally infected horses during an outbreak linked to an international equestrian event.
• The research highlights the intermittent nature of viral shedding across various sample types and the implications for controlling EHV-1 outbreaks.

Study Background

• EHV-1 is a virus causing outbreaks among horses, especially during large international equestrian events, which facilitates rapid spread across borders.
• Previous data on how the virus is shed over time within the same animals and across different biological materials were limited.
• This study aimed to fill that gap by monitoring multiple biological matrices to understand shedding dynamics during a natural outbreak.

Study Design and Methods

• Ten horses hospitalized during an outbreak linked to an international jumping competition were included.
• Duration of monitoring: 10-12 days per horse.
• Sample types collected: nasal, ocular, urine, and fecal samples.
• Total samples analyzed: 306, using quantitative real-time PCR to detect viral DNA and quantify viral load.
• Statistical analysis involved mixed-effects models to examine relationships over time and effects of vaccination status.

Key Findings on Viral Shedding

• Shedding was highly dependent on the type of biological sample:
• Nasal swabs: Highest positivity rate (76.6%), highest viral load, and longest persistence.
• Ocular samples: 49.3% positivity, lower viral load, more transient detection.
• Fecal samples: 34.6% positivity, transient detection.
• Urine samples: Lowest positivity (32.8%), transient detection.
• Within individual horses, viral shedding was frequently intermittent, with samples alternating between positive and negative results on consecutive days.
• Over time, both the probability of detecting virus and viral load decreased significantly, demonstrating a temporal decline in shedding intensity.

Impact of Vaccination

• Vaccination status did not significantly affect viral detection rates or viral load in nasal samples.
• However, vaccinated horses had a significantly lower chance of lymphopenia (a reduction in lymphocytes), suggesting vaccination modulated systemic immune responses.
• This indicates that while vaccination may not reduce viral shedding, it might improve clinical or immune outcomes.

Implications for Outbreak Management

• Intermittent and matrix-dependent shedding complicates relying on single negative PCR test results to rule out infection, risking false assumptions about a horse’s infectious status.
• Control measures should consider serial testing over time with multiple sample types to increase detection accuracy.
• Sustained isolation and monitoring are essential in high-density equestrian environments to prevent rapid international spread.
• Vaccination alone may not prevent viral shedding but is beneficial for reducing systemic effects of infection.

Conclusions

• EHV-1 shedding patterns during outbreaks are complex and vary among biological matrices and across time, often being intermittent rather than continuous.
• The study supports strategies involving repeated testing and prolonged isolation during outbreaks linked to events that gather international participants.
• Vaccination contributes to mitigating immune system impacts but does not significantly reduce viral shedding, suggesting that integrated management approaches are needed.