Background: Viliuisk encephalomyelitis is a disorder that starts, in most cases, as an acute meningoencephalitis. Survivors of the acute phase develop a slowly progressing neurologic syndrome characterized by dementia, dysarthria, and spasticity. An epidemic of this disease has been spreading throughout the Yakut Republic of the Russian Federation. Although clinical, neuropathologic, and epidemiologic data suggest infectious etiology, multiple attempts at pathogen isolation have been unsuccessful.
Methods: Detailed clinical, pathologic, laboratory, and epidemiologic studies have identified 414 patients with definite Viliuisk encephalomyelitis in 15 of 33 administrative regions of the Yakut Republic between 1940 and 1999. All data are documented in a Registry.
Results: The average annual Viliuisk encephalomyelitis incidence rate at the height of the epidemic reached 8.8 per 100,000 population and affected predominantly young adults. The initial outbreak occurred in a remote isolated area of the middle reaches of Viliui River; the disease spread to adjacent areas and further in the direction of more densely populated regions. The results suggest that intensified human migration from endemic villages led to the emergence of this disease in new communities. Recent social and demographic changes have presumably contributed to a subsequent decline in disease incidence.
Conclusions: Based on the largest known set of diagnostically verified Viliuisk encephalomyelitis cases, we demonstrate how a previously little-known disease that was endemic in a small indigenous population subsequently reached densely populated areas and produced an epidemic involving hundreds of persons.
From the aNational Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD; bInstitute of Epidemiology and Microbiology, East Siberian Scientific Center, Irkutsk, The Russian Federation; cInstitute of Health, Yakut (Sakha) Republic, Yakutsk, The Russian Federation; dInstitute of Clinical Immunology, Novosibirsk, The Russian Federation; eUW-Madison School of Veterinary Medicine, Madison, WI; fCentre National de la Recharche Scientifique, Institut Alfred Fessard, Gif-sur-Yvette, France, †Deceased; and gBinghampton University, SUNY, Binghampton, NY.
Submitted 5 May 2008; accepted 24 June 2009.
Supported by the BioTechnology Engagement Program of the US Department of Health and Human Services and also by the Intramural Research Program of the National Institute of Neurological Disorders and Stroke, National Institutes of Health.
Correspondence: Lev G. Goldfarb, National Institutes of Health, Room 4S06, 5625 Fishers Lane, MSC 9404, Bethesda, MD 20892–9404. E-mail GoldfarbL@ninds.nih.gov.