Outbreak of neurologic disease caused by equine herpesvirus-1 at a university equestrian center.
Authors: Henninger Rick W, Reed Stephen M, Saville William J, Allen George P, Hass Gregory F, Kohn Catherine W, Sofaly Cheryl
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: EHV-1 Myeloencephalopathy Outbreak During a substantial outbreak affecting 135 horses at a university equestrian facility, researchers documented clinical, serologic, virologic and management factors associated with equine herpesvirus-1 (EHV-1) myeloencephalopathy to identify risk factors for this serious neurologic manifestation of EHV-1 infection. Of the 117 horses showing signs of EHV-1 infection across the facility, 46 developed neurologic deficits characterised by symmetrical hind limb ataxia and weakness, with 12 becoming recumbent and fatal; critically, age over 5 years, location in south-facing or arena stalls, and fever persisting to day 3 or later of the febrile period emerged as significant risk factors for developing neurologic disease. The most predictive factors for severe neurologic disease and death were age >5 years, peak rectal temperatures >103.5°C, and fever that peaked on or after day 3 of illness—findings that align with previous research and provide practitioners with identifiable prognostic markers during outbreaks. Encouragingly, horses that survived showed complete recovery to pre-outbreak exercise capacity within 12 months, though those developing severe neurologic deficits during the acute phase retained residual impairment at 6-month follow-up. These results offer farriers, vets and equestrian managers practical clinical indicators to identify at-risk individuals early in EHV-1 outbreaks and highlight the importance of monitoring temperature trends and managing housing conditions, particularly for older horses, to mitigate neurologic complications.
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Practical Takeaways
- •Older horses (>5 years) and those with delayed fever peaks (day 3+) are at highest risk for developing neurologic complications from EHV-1; monitor these horses closely during outbreaks
- •Facility location and housing arrangement (south-facing and arena stalls) may influence disease severity—consider management changes during outbreaks
- •Expect a good long-term prognosis for surviving horses, with most returning to normal function within a year despite initial neurologic signs
Key Findings
- •Of 135 horses, 117 showed EHV-1 infection signs with 46 developing neurologic deficits and 12 becoming recumbent and non-surviving
- •Risk factors for neurologic disease included age >5 years, location in south or arena stall areas, and rectal temperature >103.5°F occurring on day 3 or later of fever
- •All surviving horses returned to pre-outbreak exercise levels within 1 year, though those with severe neurologic deficits showed residual deficits at 6-month examination
- •Acyclovir was used prophylactically and therapeutically during the outbreak with outcomes described