Clinical and neuropathological features of West Nile virus equine encephalomyelitis in Italy

West Nile (WN) virus infection is a mosquito-borne flavivirosis endemic in Africa and Asia. Clinical disease is usually rare and mild and only in a fe w cases the infection causes encephalomyelitis in horses, fever and meningo encephalitis in man. We report here the clinical and pathological findings in an epidemic of the disease involving 14 horses from Tuscany, Italy. All cases were observed from August to October 1998, Affected horses showed ata xia, weakness paresis of the hindlimbs and, in 6 cases, there was parapares is progressing to tetraplegia and recumbency within 2 to 9 days. Eight anim als recovered without any important consequences. Serological: investigatio ns revealed positivity to WN virus in all the 14 horses and the agent was i solated from the cerebellum and spinal cord of an affected horse. Postmorte m examination was carried out on 6 horses. The neuropathological pattern wa s that of a mild to moderate, nonsuppurative polioencephalomyelitis with co nstant involvement of the ventral horns of the thoracic and lumbar spinal c ord, where focal gliosis and haemorrhage were also apparent in some cases. Differential diagnoses with other equine viral encephalomyelitides are disc ussed. Climatological and environmental characteristics of the geographic a rea in which the outbreaks occurred suggest the existence of suitable condi tions for the development of the disease. This is the first report of WN vi rus equine encephalomyelitis in Italy.