Japanese encephalitis in a racing thoroughbred gelding in Hong Kong.
Authors: Lam K H K, Ellis T M, Williams D T, Lunt R A, Daniels P W, Watkins K L, Riggs C M
Journal: The Veterinary record
Summary
# Editorial Summary: Japanese Encephalitis in a Racing Thoroughbred A vaccinated racing thoroughbred gelding in Hong Kong presented with pyrexia progressing to hyperexcitability and severe self-trauma, prompting comprehensive clinical, pathological and serological investigation. Diagnosis was confirmed through detection of Japanese encephalitis virus genomic sequences in spinal cord tissue, with phylogenetic analysis of the E gene and NS5-3'UTR sequences revealing a novel recombinant form clustering divergently from previously documented genotypes I and II. Although horses are regarded as dead-end hosts for the virus, this case demonstrated that breakthrough infection could occur despite vaccination, raising important questions about vaccine efficacy and the risk of viral circulation within equine populations. The finding has significant implications for equine health policy, particularly regarding movement restrictions and the adequacy of current vaccination protocols in endemic regions like Hong Kong. Practitioners should be aware that Japanese encephalitis remains a consideration in the differential diagnosis of acute neurological disease in vaccinated horses in at-risk areas, and the emergence of novel genotypes may necessitate reassessment of vaccination strategies and biosecurity measures to protect national herds.
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Practical Takeaways
- •Even vaccinated horses can develop Japanese encephalitis in endemic regions; vaccination does not guarantee absolute protection and ongoing surveillance is warranted
- •Neurological cases presenting with pyrexia and hyperexcitability in endemic areas should include Japanese encephalitis in the differential diagnosis
- •A single infected horse in a population has industry-wide implications for biosecurity measures, trade restrictions, and herd health management protocols
Key Findings
- •A vaccinated horse in Hong Kong developed Japanese encephalitis with pyrexia, hyperexcitability, and self-trauma despite previous vaccination
- •Japanese encephalitis was confirmed by detection of viral genomic sequences in spinal cord tissue and serological observations
- •Phylogenetic analysis suggested possible recombinant infection between genotype I and genotype II Japanese encephalitis viruses
- •The case had significant implications for Hong Kong's horse industry including restrictions on horse movement and review of vaccination protocols