Additionally, we also determined the presence of persisting virus in the brain and kidney of all mice that had survived infection (euthanized on day 14 p.i.)with the highest dose of the different mutant virus strains (NS1, n = 8; NS2A, n = 1; NS3, n = 2; and NS4B249, n = 3) using qRT-PCR. This evidence concerns the gene KRAS and infection.