Nucleotide sequence identifies Vilyuisk virus as a divergent Theiler's virus.

The Vilyuisk virus, originally thought to be the cause of a degenerative neurological disease of inhabitants of Siberia, has been characterized by sequence analysis of its 5' noncoding and coat protein coding regions. In the 5' noncoding, leader, and VP4 regions, the nucleotide identity between the sequences of known strains of Theiler's virus and Vilyuisk virus is about 90%. In the VP1-encoding region, the similarity drops to about 66% compared to the 50% similarity between sequences of Theiler's virus and encephalomyocarditis virus. Using the known crystal structure of one Theiler's virus strain, it is shown that the sequence heterogeneities generally occur at exposed surface residues. Vilyuisk virus is the most divergent Theiler's virus known. A tissue culture-adapted isolate has been propagated and found to exhibit low neurovirulence in CD-1 mice.