Avian influenza virus(34) SARS-CoV-2(22) pathogenicity(21) hepatitis E virus(20) zoonosis.(18) H9N2(16) H5N1(12) Pathogenesis(12) Avian Influenza(11) influenza A virus(11) H1N1(10) PIGS(10) wild birds.(9) mice(9) Vaccine(9) Co-infection(8) vaccine.(8) chicken(8) Transmission(8) HEV(8) Pathogenicity.(7) immune response(7) Influenza virus(7) chickens(7) Transmissibility(7) Mutation(6) virus(6) influenza A(6) hemagglutinin(6) Swine influenza.(6)