Clinical and neuropathological features of West Nile virus equine encephalomyelitis in Italy.
Authors: Cantile C, Di Guardo G, Eleni C, Arispici M
Journal: Equine veterinary journal
Summary
# West Nile Virus Encephalomyelitis in Horses: An Italian Case Series West Nile virus, a mosquito-borne flavivirus traditionally associated with African and Asian endemic areas, rarely causes severe neurological disease in horses, yet an outbreak in Tuscany during summer and autumn 1998 demonstrated its potential for significant clinical impact when it does. The research team documented clinical presentation and neuropathological findings across 14 naturally infected horses, with affected animals presenting progressive hindlimb ataxia and paresis that advanced to tetraplegia and recumbency within 2–9 days in the most severely affected cases; serological confirmation and viral isolation from neural tissue confirmed West Nile virus as the causative agent. Histopathological examination of six post-mortem cases revealed a consistent pattern of mild to moderate nonsuppurative polioencephalomyelitis with specific targeting of ventral horn neurons in the thoracic and lumbar spinal cord, accompanied by focal gliosis and haemorrhage in some individuals. Encouragingly, eight of the 14 horses recovered without major residual neurological deficit, suggesting a variable disease course. For equine practitioners, this first documented Italian case series underscores the importance of considering West Nile virus in the differential diagnosis of equine encephalomyelitis—particularly during warmer months and in areas with suitable environmental conditions for Culex mosquito populations—and highlights that whilst clinical disease remains uncommon relative to infection rates, the neurological manifestations when they occur warrant aggressive supportive care and monitoring.
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Practical Takeaways
- •West Nile virus should be included in differential diagnoses for horses presenting with acute ataxia, hindlimb paresis, or progressive tetraplegia, particularly during late summer and autumn months
- •Geographic regions with suitable climatological and environmental conditions may support WN virus transmission via mosquito vectors—implement appropriate vector control and biosecurity measures
- •Prognosis is relatively favorable with 57% recovery rate in this outbreak; however, cases progressing to recumbency may require intensive management and supportive care
Key Findings
- •14 horses in Tuscany presented with WN virus infection causing encephalomyelitis from August to October 1998, with hindlimb weakness progressing to tetraplegia in 6 cases within 2-9 days
- •8 of 14 affected horses recovered without significant sequelae
- •Neuropathological examination of 6 necropsied horses revealed mild to moderate nonsuppurative polioencephalomyelitis with constant involvement of ventral horns in thoracic and lumbar spinal cord
- •WN virus was isolated from cerebellum and spinal cord, with all 14 horses showing serological positivity