An ocular infection model using suckling hamsters inoculated with equine herpesvirus 9 (EHV-9): kinetics of the virus and time-course pathogenesis of EHV-9-induced encephalitis via the eyes.
Authors: El-Habashi N, Kato Y, El-Nahass E, Fukushi H, Hirata A, Sakai H, Kimura J, Yanai T
Journal: Veterinary pathology
Summary
# Editorial Summary: Ocular EHV-9 Infection and Neuroinvasion Pathways Researchers developed a suckling hamster model of equine herpesvirus 9 (EHV-9) infection via conjunctival inoculation to investigate how this neurotropic virus spreads from the eye to the central nervous system, examining viral kinetics and brain pathology across nine timepoints over 144 hours post-infection. Histological examination revealed early epithelial necrosis and inflammatory infiltration in ocular tissues within 6–24 hours, whilst immunohistochemistry demonstrated viral antigen in macrophages and nerve terminals supplying the eyelid, extraocular muscles, and lacrimal glands; by 96 hours, encephalitis developed in the brainstem, particularly at the level of the pons and cerebellum. The findings suggest EHV-9 exploits multiple cranial nerve routes—including the trigeminal, abducent, oculomotor, and facial nerves—to access the brain from ocular tissues. Although this work used a small-animal model rather than equine subjects, the documented neuroinvasion pathway and temporal progression offer valuable insights into how neurotropic herpesviruses can establish CNS infection via seemingly peripheral routes, potentially informing understanding of EHV-9 and related neurotropic viruses in horses presenting with encephalitis or unexplained neurological signs. The model itself provides a practical framework for testing antiviral interventions targeting early viral spread through cranial nerves.
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Practical Takeaways
- •This research demonstrates a potential neuroinvasive pathway for EHV-9 through ocular tissues to the central nervous system, which may be relevant to understanding how equine herpesviruses can cause neurological disease in horses
- •The study establishes that conjunctival exposure to EHV-9 can lead to systemic neurological involvement within 4 days, suggesting ocular symptoms may warrant investigation for potential neurological complications
- •The identification of multiple cranial nerve involvement in viral spread suggests that comprehensive neurological examination may be warranted in horses with suspected herpesvirus-related ocular disease
Key Findings
- •EHV-9 induced conjunctival epithelial necrosis and inflammatory cell infiltration within 6-24 hours post-inoculation via conjunctival route
- •Viral antigen was detected in macrophages around nerve endings of the eyelid, extraocular muscles, and lacrimal glands from 6-144 hours post-inoculation
- •Encephalitis developed in the brainstem (pons and cerebellum) by 96 hours post-inoculation
- •EHV-9 invaded the brain via multiple cranial nerves (trigeminal, abducent, oculomotor, and facial nerves) following conjunctival inoculation