The importance of the duck cytotoxic T cell response in eradicating the H5N1 infection in vivo was suggested by an investigation through the detection of significantly more CD8+ cells and the increased expression of cytotoxicity-related genes, such as granzyme A and IFN, in PBMCs from 5 to 9 days post-infection in mallard duck infection experiments. The gene discussed is CD8A; the disease is infection.