[Molecular epidemiology of ECHO 6 virus, the causative agent of the 2006 outbreak of serous meningitis in Khabarovsk].

A reverse genetics approach was applied to generate variants of avian influenza virus A/FPV/Ro/34 (H7N1) containing mutations in the caspase cleavage sites of NP and M2 proteins. Mutation Gly16 --> Asp in avian virus NP made this protein (NPgd) sensitive to caspases, like human virus NP, and permitted its cleavage in infected cells. Mutant recombinant virus NPgd was able to replicate and stably carried Gly --> Asp mutation during passages in cultured cells, chicken eggs, and chickens. This variant was found to have significantly decreased virulence for chickens comparatively to wild type recombinant virus (wtr). Virus variants characterized by deletion Gly16 in NP (NPdel) and mutated caspase cleavage site VDVDD87 --> VNVND87 in M2 (M2nn) protein were shown to lack intracellular caspase-dependent cleavage of NP and M2, respectively, and to retain their ability to replicate in different hosts. Variant NPdel, like wide type virus, displayed a high chicken virulence whereas M2nn, like NPgd one, was found to possess a low virulent phenotype. The findings suggest that the mutations altering natural caspase cleavage motifs in NP and M2 do not restrict virus replication ability but can significantly reduce the virulent potential of the mutant viruses. Recombinant virus variants with altered caspase cleavage motifs could be proposed as a matrix for the design of live recombinant vaccines.