Molecular cloning of the complete genome of Theiler's virus, strain DA, and production of infectious transcripts.

We constructed a complete cDNA clone of the genome of Theiler's virus strain DA in a Bluescript plasmid. This recombinant plasmid, called pTMDA, was used to synthesize full length RNA transcripts of the viral insert. The RNA was infectious for BHK cells. Virus R1-DA, obtained from transfected BHK cells, caused the biphasic disease classically observed with this strain of Theiler's virus. SJL/J mice did not show clinical symptoms during the first week following intracranial inoculation, although viral antigens were found in a few neurons of brain and spinal cord. By 45 days post-inoculation, the mice had developed a chronic demyelinating disease and viral RNA and antigens could be found only in spinal cord white matter in areas surrounded by inflammatory infiltrates. At this stage no RNA or antigens were found in neurons. Therefore the phenotype of R1-DA was indistinguishable from that of genuine DA Theiler's virus.