JEVNSW/22 was less virulent than JEVFU (genotype 2) and JEVNakayama (genotype 3) in C57BL/6J mice and in interferon regulatory factor 7 deficient (Irf7−/−) mice, with infection of wild-type and knockout murine embryonic fibroblasts indicating JEVNSW/22 is more sensitive to type I interferon responses. Here, IRF7 is linked to infection.