SH2D3C and infection: Infections with SFV A7(74) are avirulent in adult mice, as mentioned above but a recombinant A7(74) virus, having an Arg in place of the opal stop codon (rA774-arg), as in SFV4, shows increased pathogenicity, despite still being far less virulent than SFV4 or when the entire nsP3 was exchanged [38,39].