CASP2 and infection: As shown in Figure 7, part of the apoptotic proteases were down-regulated in the control group at 4 hpi, such as caspase 1, caspase 2, caspase 3, caspase 7 and caspase 10, while anti-apoptotic factor mcl1 was up-regulated (p > 0.05), revealing that intestinal apoptosis might occur rapidly post-infection in the control group and thereby lead to host feedback regulation.