At 36 h post-infection, a typical CPE of the Vero cell-adapted IBV, that is, the formation of giant syncytium cells, was observed in cells infected with rIBV-Beau-KC(S1)-p10V6, which carries G21556C and C22077T mutations, but no CPE was observed in the cells infected with rIBV-Beau-KC(S1)-p4V9 carrying the C22077T mutation only (Figure 2E). The gene discussed is CALCA; the disease is infection.