Search

Global spread and regional endemicity of H5Nx Goose/Guangdong avian influenza viruses (AIV) pose a continuous threat for poultry production and zoonotic, potentially pre-pandemic, transmission to humans. Little is known about the role of mutations in the viral neuraminidase (NA) that accompanied bird-to-human transmission to support AIV infection of mammals. Here, after detailed analysis of the NA sequence of human H5N1 viruses, we studied the role of A46D, L204M, S319F and S430G mutations in virus fitness in vitro and in vivo. Although H5N1 AIV carrying avian- or human-like NAs had similar replication efficiency in avian cells, human-like NA enhanced virus replication in human airway epithelia. The L204M substitution consistently reduced NA activity of H5N1 and nine other influenza viruses carrying NA of groups 1 and 2, indicating a universal effect. Compared to the avian ancestor, human-like H5N1 virus has less NA incorporated in the virion, reduced levels of viral NA RNA replication and NA expression. We also demonstrate increased accumulation of NA at the plasma membrane, reduced virus release and enhanced cell-to-cell spread. Furthermore, NA mutations increased virus binding to human-type receptors. While not affecting high virulence of H5N1 in chickens, the studied NA mutations modulated virulence and replication of H5N1 AIV in mice and to a lesser extent in ferrets. Together, mutations in the NA of human H5N1 viruses play different roles in infection of mammals without affecting virulence or transmission in chickens. These results are important to understand the genetic determinants for replication of AIV in mammals and should assist in the prediction of AIV with zoonotic potential. Author summary: Avian influenza viruses (AIV) including viruses of the H5Nx Goose/Guangdong-lineage caused hundreds of human infections and fatalities worldwide and pose a continuous zoonotic and pandemic threat. It is important to understand the role of mutations that support AIV-infection in mammals after bird-to-human transmission. Here, we describe the prevalence and the role of mutations in the viral neuraminidase (NA), which is mainly responsible for virus release from infected cells, preferentially selected in human H5N1 viruses. Compared to their avian ancestors, human-like H5N1 had less NA in virus particles and exhibited lower NA activity conferred mainly by the L204M substitution. Furthermore, NA mutations increased the binding of H5N1 to human-type receptors, acted synergistically to confer high virus replication in avian and human cells and/or modulated virulence and replication in mice, but not in chickens. This study is important to understand the genetic and biological properties of human AIV and will help to predict zoonotic potential AIV. [ABSTRACT FROM AUTHOR]