Viliuisk encephalomyelitis in Eastern Siberia - analysis of 390 cases.

Viliuisk encephalomyelitis (VE) is a unique disease occurring in the Yakut (Sakha) population of Eastern Siberia. VE is always fatal, with some patients dying during the acute encephalitic phase of illness; those surviving the acute phase develop progressive dementia, rigidity and spastic quadriparesis as part of a more prolonged pan-encephalitic syndrome. The disease is characterized neuropathologically by multiple widespread micronecrotic foci with marked inflammatory reactions and subsequent gliosis throughout the cerebral cortex, basal ganglia, cerebellum and brain stem. The acute febrile onset with cerebrospinal fluid pleocytosis and increased protein and neuropathology showing inflammatory reactions suggest that VE is an infectious disease, but the causative agent has not been identified. Initially detected in a small mixed Yakut-Evenk population of the mid-Viliui region, the disease subsequently spread south to densely populated areas around the capital city of Yakutsk. The occurrence of secondary VE cases in households and the introduction of the disease by migrants into new populations indicate that the disease is horizontally transmitted in a setting of a long intra-household contact. Although there has been a recent decline in the number of cases, increasing travel may result in further spread of this fatal disease to susceptible individuals in other regions of the world.