Equine Herpesvirus (EHV, or rhinopneumonitis)

Disease Overview

Equine herpesvirus type 1 (EHV-1) and equine herpesvirus type 4 (EHV-4) infect the respiratory tract, causing disease that ranges from minor to severe. EHV-1 can also cause late-term abortions, early foal death and neurologic disease. EHV can affect horses of any age, with most horses exposed at a young age and becoming latent carriers for life. Stress (transportation, foaling, surgery, other diseases) can cause activation of latent EHV, causing clinical signs and shedding of virus via nasal secretions.

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Transmission

EHV spreads directly in aerosolized droplets dispersed by coughing or direct contact (nose-to-nose). It spreads indirectly through fomite transmission—hands, clothing, vehicles and trailers, stalls, and common-use articles such as brushes, buckets and bits can all spread EHV-1. It can also be transmitted through contact with placental and fetal fluids and tissues from fetuses aborted due to EHV-1.

Clinical Signs

  • Fever (>101.5°)
  • Coughing
  • Nasal discharge
  • Lethargy/depression
  • Neonatal death (most commonly associated with EHV-1)
  • Late-term abortion (7+ months) (most commonly associated with EHV-1)

Risk Factors

  • Travel
  • Frequent contact with large numbers of horses
  • Exposure to horses that have traveled
  • Compromised or immature immune system

References

“Equine Herpesvirus (Rhinopneumonitis),” American Association of Equine Practitioners, copyright 2021, aaep.org/risk-based-vaccination-guidelines/equine-herpesvirus-rhinopneumonitis.

“Equine Herpesvirus type 1 (EHV-1) Respiratory and Reproductive Disease Quick Facts,” Merck Animal Health, copyright 2021, www.merck-animal-health-equine.com/styles/images/programs/EHV_Infographics.pdf