TFF2 and infection: In the group infected with 5 × 105 PFU, at least four (66.7%) of the six mice inoculated with rKUNV-LP, rKUNV-LP-ET332K, or SP-B survived throughout the observation period, but all mice inoculated with rKUNV-LP-EF156S died within 9 days post-infection (Figure 5D).