Authors: Pusterla Nicola, Barnum Samantha, Lawton Kaila, Wademan Cara, Corbin Rachel, Hodzic Emir
Journal: Journal of equine veterinary science
Summary
# EHV-1 Genotype Distribution and Clinical Disease Expression in US Horses (2019–2022) The epidemiological landscape of equine herpesvirus-1 infection has shifted considerably, with the traditionally non-neuropathogenic N752 genotype now responsible for a substantial proportion of neurological cases (equine herpesvirus myeloencephalopathy or EHM), challenging historical assumptions about genotype-phenotype relationships. Pusterla and colleagues analysed 297 EHV-1 qPCR-positive samples collected across the United States between 2019 and 2022, utilising allelic discrimination assays to identify three distinct genotypes (N752, D752 and the recently emerged H752) across respiratory disease, EHM and abortion cases. The N752 genotype dominated all three clinical presentations—accounting for 87.5% of respiratory cases, 74.3% of EHM cases and 80% of abortions—whilst the neuropathogenic D752 appeared in 9.3% of respiratory and 25.7% of neurological cases, and the novel H752 variant remained restricted to 3.1% of respiratory cases with no evidence of geographic spread since its 2021 identification. These findings suggest that whilst N752 has historically been considered less virulent, contemporary strains may confer greater capacity for neurological disease expression, necessitating a reassessment of diagnostic protocols and preventive strategies that currently rely on genotype assumptions. For practitioners managing EHV-1 outbreaks, particularly those involving neurological complications, genotyping may help refine risk stratification and inform tailored antimicrobial and supportive care protocols, though the predominance of N752 in EHM cases indicates that clinical phenotype cannot be reliably predicted
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Practical Takeaways
- •N752 is now the dominant genotype causing EHM in addition to respiratory disease and abortion, representing a shift from historical prevalence patterns—veterinarians should update their understanding of EHM epidemiology
- •The H752 variant remains geographically contained and has not spread widely since 2021, suggesting current biosecurity and management practices may be effectively controlling its transmission
- •Winter and spring seasons show highest EHV-1 activity, suggesting intensified monitoring and preventive protocols should target these periods
Key Findings
- •N752 genotype was predominant across all disease presentations: 87.5% in respiratory cases, 74.3% in EHM cases, and 80% in abortions
- •D752 genotype was detected in 9.3% of respiratory cases and 25.7% of EHM cases, with no detection in abortion cases
- •H752 genotype was detected only in 3.1% of respiratory cases and remained geographically and temporally clustered since first US report in 2021 with no evidence of emerging spread
- •EHV-1 qPCR-positive cases predominated during winter and spring seasons