Comparison of clinical variables and outcome of 2 natural equine herpesvirus myeloencephalopathy outbreaks induced by equine herpesvirus-1 A2254/N752 strain in sport horses.
Authors: de la Cuesta-Torrado María, Velloso Alvarez Ana, Cárdenas-Rebollo José Miguel, Neira-Egea Patricia, Vitale Valentina, Cuervo-Arango Juan
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: EHV-1 Myeloencephalopathy Outcomes – Insights from Two Recent Outbreaks Equine herpesvirus-1 myeloencephalopathy (EHM) presents a significant clinical challenge, yet comparative data on disease progression and management outcomes remain limited. Researchers at a Spanish veterinary teaching hospital conducted a retrospective analysis of 35 sport horses affected across two natural EHM outbreaks (2021 and 2023), both caused by the same A2254/N752 strain, examining clinical presentation, treatment protocols, and patient outcomes through hospital records and owner surveys. Despite comparable initial ataxia grades and exposure to identical virus strains, the 2021 cohort experienced substantially worse outcomes: a 32% fatality rate versus zero deaths in 2023, longer hospitalisation periods, and only 11.7% return to competition within six months compared with 100% in the 2023 group—a striking disparity that was not explained by different treatment approaches. The critical differentiator proved to be the development of systemic complications; horses presenting with concurrent urinary dysfunction and clinical signs of vasculitis (both observed in 2021 but absent in 2023) correlated strongly with poor prognosis, suggesting these complications rather than neurological severity alone determine survival and athletic recovery. For practitioners, this emphasises the importance of vigilant monitoring for urinary retention and vascular complications as prognostic indicators in EHM cases, as early recognition and management of these systemic manifestations may meaningfully improve both survival and functional recovery in affected sport horses.
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Practical Takeaways
- •Systemic complications such as urinary dysfunction and signs of vasculitis during EHM outbreaks are critical prognostic indicators—horses developing these require intensive monitoring and management as they have significantly worse outcomes regardless of initial neurological severity
- •Even identical EHV-1 strains can cause variable disease severity between outbreaks; clinical context matters for prognosis and the presence of secondary complications is more predictive than the causative strain alone
- •Early recognition and aggressive management of systemic signs (urinary/vascular complications) may be key to improving survival and return-to-competition rates in EHM cases
Key Findings
- •Two EHM outbreaks caused by identical A2254/N752 EHV-1 strain showed markedly different severity: 32% fatality in 2021 outbreak versus 0% in 2023 outbreak (P < 0.001)
- •Horses in 2021 outbreak experienced concurrent urinary and vascular complications associated with poor prognosis, whereas 2023 outbreak horses did not develop these systemic complications (P = 0.01)
- •Recovery to competition was significantly better in 2023 (100% return within 6 months) compared to 2021 (11.7%), despite equivalent ataxia severity at admission
- •Longer treatment duration with flunixin meglumine and dimethyl sulfoxide in 2021 correlated with higher disease severity and worse outcomes