Histopathologic Findings Following Experimental Equine Herpesvirus 1 Infection of Horses.
Authors: Holz Carine L, Sledge Dodd G, Kiupel Matti, Nelli Rahul K, Goehring Lutz S, Soboll Hussey Gisela
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: EHV-1 Tissue Damage and Long-Term Complications Equine herpesvirus 1 (EHV-1) causes a spectrum of clinical disease ranging from respiratory infection to the devastating neurological form (EHM), yet relatively little is known about how different viral strains damage tissues beyond the acute phase. Researchers infected horses with three EHV-1 variants of differing neuropathogenic potential and performed detailed histopathological analysis at either acute disease onset or 10 weeks post-infection. Whilst only 3 of 8 horses infected with wild-type Ab4 developed EHM (with vasculitis and lymphocytic infiltrates in the CNS, lungs, endometrium and eyes), a concerning finding emerged in all male horses: interstitial inflammation and viral antigen within testicular tissue across all three viral strains, alongside mild ocular inflammation (choroiditis) persisting in multiple animals, particularly those infected with the gD4 mutant strain. These results suggest EHV-1 establishes persistent tissue-level changes beyond acute neurological disease, raising important questions about long-term reproductive viability, semen shedding as an infection vector, and ocular complications that clinicians should monitor during recovery and rehabilitation protocols.
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Practical Takeaways
- •EHV-1 infection poses significant reproductive risks in male horses, with potential for prolonged virus shedding via semen; breeding soundness evaluation should consider post-infection testicular changes
- •Mild ocular inflammation (choroiditis) may persist long-term in EHV-1 infected horses without obvious clinical signs—monitor eyes regularly and consider implications for athletic performance
- •Different viral strains show varying pathogenicity; the gD4 mutant caused choroiditis in all infected horses, suggesting strain-specific tissue tropism affects clinical outcomes
Key Findings
- •3 of 8 horses infected with wild-type EHV-1 (Ab4) developed EHM with lymphohistiocytic vasculitis in lungs, spinal cord, endometrium and eyes; 2 required euthanasia by day 9
- •Mild choroiditis persisted in 50% of remaining Ab4-infected horses, 44% of Ab4 N752-infected horses, and 100% of Ab4 gD4-infected horses at 10 weeks
- •All male horses (n=8) developed interstitial lymphoplasmacytic and/or histiocytic orchitis with EHV-1 antigen detected, raising concerns for prolonged viral shedding through semen
- •Only animals with clinical EHM showed overt vasculitis in CNS and eye, while choroiditis and orchitis occurred with or without neurologic signs