Infectious cDNA clones of tick-borne encephalitis virus European subtype prototypic strain Neudoerfl and high virulence strain Hypr

Infectious cDNA clones of two strains of tick-borne encephalitis (TBE) virus, i.e. European subtype prototypic strain Neudoerfl and the closely related but more virulent strain Hypr, were constructed. The recombinant constructs consisted of cDNAs stably inserted into the bacterial plasmid pBR322 under the control of T7 promoter elements. The genome of TBE virus strain Neudoerfl was successfully cloned, both as a full-length cDNA and as two partial cDNAs. In the case of strain Hypr, the genome is represented by two cDNA clones corresponding to the 5'- and 3'-terminal halves of the genome. Highly infectious RNAs can be produced from the full-length cDNA clone or from the partial clones ligated in vitro to form full-length cDNA templates prior to T7 transcription. The biological properties of the recombinant progeny viruses, including virulence characteristics, were indistinguishable from the corresponding parent virus strains. Thus, the described infectious cDNA clones represent a useful and reliable experimental system for the specific mutagenesis of TBE virus.