Positive selection pressure on the B/C domains of the E2-gene of classical swine fever virus in endemic areas under C-strain vaccination

► We evaluate the positive selection pressure on E2 partial gene of CSF fever viruses. ► We asses a representative CSF virus for their clinical virulence. ► The analysis estimated six new sites under positive selection. ► Experimental evidence of a milder presentation of the disease is provided. ► Escape viral variants with alterations in viral pathogenicity are suggested to occur.