Understanding how host factors influence viral evolution could revolutionize our approach to pandemic preparedness and vaccine design. While epidemiologists have long observed that flu severity varies between populations and sexes, the underlying evolutionary mechanisms remained mysterious until now.
Researchers tracked influenza A virus adaptation across 28 independent lineages in male and female mice from two genetically distinct strains—BALB/c and C57BL/6. Using three-dimensional protein mapping, they identified hotspots where mutations repeatedly emerged under selection pressure. In BALB/c mice, viral adaptation consistently favored nonsynonymous mutations that increased virulence, with certain hemagglutinin variants becoming fixed exclusively in female-adapted lineages. Most striking was sex-dependent selection on the NS1 protein interface: mutations disrupting a critical dimerization motif concentrated on a single residue in female-adapted viruses but scattered across the entire interface in male-adapted variants.
This finding challenges the assumption that viral evolution follows uniform pathways regardless of host characteristics. The discovery that C57BL/6 adaptation produced fewer mutations but fundamentally altered defective viral genome formation—leading to reduced cell damage and attenuated virulence—suggests host genetics can redirect viral evolutionary trajectories through entirely different mechanisms. For human health implications, this research indicates that pandemic preparedness strategies may need to account for population-specific genetic backgrounds and sex-based differences in viral adaptation. The work also suggests that defective viral genomes, previously considered random byproducts, may be systematically influenced by host genetics, potentially offering new therapeutic targets for antiviral development.