SFTPB and infection: In the group infected with 5 × 104 PFU, one (16.7%), three (50%), and four (66.7%) out of six mice inoculated with rKUNV-LP, rKUNV-LP-ET332K, and SP-B, respectively, died within the observation period, whereas all rKUNV-LP-EF156S-infected mice died by 10 days post-infection (Figure 5C).