In the intricate dance between viruses and their hosts, the early phases of pandemics are marked by rapid viral evolution aimed primarily at enhancing transmissibility and replication efficiency rather than immune evasion. Despite significant advances in virology, the precise manner in which host genetics and biological sex contribute individually and synergistically to this viral adaptation remains largely uncharted territory. A groundbreaking study from the University of Utah now illuminates facets of this complex interaction, indicating that certain host profiles may act as “evolutionary accelerators,” expediting viral virulence in novel and unexpected ways.
Rodrigo Costa, the study’s lead author and a postdoctoral researcher at the University of Utah’s School of Biological Sciences, underscores the implications of these findings. “Our data show that certain hosts select for mutations linked with increased virulence, mutations that not only amplify the virus’s pathogenicity within those hosts but can also worsen outcomes across the broader population,” he explains. Intriguingly, the study reveals this accelerated virulence is predominantly observed in female mice of specific genetic backgrounds—a discovery that challenges conventional assumptions about viral evolution pathways.
Published under the title “Host genotype and sex shape influenza evolution and defective viral genomes” in the prestigious journal Nature Communications, this NIH-funded research opens new avenues for understanding the evolutionary pressures viruses face in different hosts. The investigators employed experimental evolution techniques with influenza A virus to dissect the nuanced roles host genetics and sex play in shaping viral evolutionary trajectories during the critical initial stages of infection.
The premise driving this research questions whether more resistant host genotypes paradoxically expedite the evolution of viral virulence. By examining how influenza viruses evolve in genetically distinct male and female mice, the scientists demonstrate how host-specific factors can substantially influence the pathogen’s genetic diversification and virulence potential. Such insights are pivotal for refining epidemiological models and tailoring public health interventions, as they bring to light the biological variables that might determine population-level disease outcomes.
Principal investigator Wayne Potts highlights the study’s unexpected revelations: “While we hypothesized that greater viral genetic diversity, facilitated by mixing viruses from multiple hosts, would predominantly drive virulence evolution, our data indicate that host sex and genotype wield a far more profound influence. Furthermore, it is the more resistant hosts that appear to selectively pressure the virus towards higher virulence.” This nuanced understanding contradicts the simplistic notion that viral evolution is purely a string of random mutations seeking immune evasion.
Central to the experimental design were two widely-used laboratory mouse strains—BALB/c and C57BL/6, which differ genetically and immunologically. By serially passaging the A/Hong Kong/1/1968 H3N2 influenza virus, the original strain responsible for the devastating Hong Kong flu pandemic, through male and female mice of these strains, the researchers monitored viral adaptation over ten infection cycles. This simulated early pandemic conditions, capturing the virus’s initial encounter with naïve hosts and the consequent evolutionary pressures.
Throughout the passages, careful quantitative measurements of viral replication rates, virulence (assessed through host weight loss and mortality), and genomic sequencing of evolved viruses were conducted. A particularly innovative approach employed was the mapping of viral mutations onto three-dimensional structures of influenza proteins, enabling a functional interpretation of how specific amino acid changes affected viral fitness and immune interaction.
Intriguingly, the study identified that the virus evolved dramatically differently in female BALB/c mice, where it gained heightened virulence, compared to its relatively muted evolutionary changes in C57BL/6 mice. This differential adaptation appears rooted in the distinct immunological milieu shaped by host sex and genotype. For instance, mutations localized to the NS1 viral protein—a key antagonist of host innate immunity—clustered distinctly in viruses passaged through female hosts, implying sex-specific immune pressures shape the viral mutation landscape.
Furthermore, viruses replicating in the genetically distinct C57BL/6 mice accumulated fewer adaptive mutations but produced higher quantities of defective viral genomes (DVGs). These genomes, often truncated or mutated, cannot replicate independently and interfere with standard viral replication cycles, potentially modulating virulence and immune activation. This discovery provides the first live-animal evidence that host genotype may influence the balance between productive and defective viral genome production, adding a new layer to our understanding of viral pathogenesis.
The implications of these findings ripple beyond murine models. If similar dynamics occur in humans, host genetics and sex could be critical determinants of viral evolution during pandemics. Rodrigo Costa envisions future strategies where genomic surveillance combined with host profiling might enable public health officials to prioritize vaccination or other interventions for individuals more likely to select for increased viral virulence, thereby potentially mitigating overall disease severity.
Beyond the immediate scientific insights, this research spotlights the utility of experimental pathogen evolution as a method to unravel the intricacies of host-pathogen interactions. By emulating early infection dynamics under controlled laboratory conditions, scientists can probe evolutionary outcomes that are otherwise challenging to predict or observe in real-world outbreaks.
While these insights deepen our grasp of viral ecology and evolution, the authors caution against overgeneralizing from mouse models to human viral evolution without further studies. The complex interplay of immune defenses, hormonal environments, and genetic variability in humans necessitates comprehensive research before translating these findings into clinical or public health applications.
Nevertheless, this study marks a pivotal advance in virology by revealing that the host’s biological sex and genetic makeup do not merely influence susceptibility to infection but actively direct the evolutionary pathways of viruses. The identification of hosts as potential ‘evolutionary accelerators’ reframes our understanding of pathogen emergence and highlights the intricate biological battleground that determines the trajectory of infectious disease outbreaks.
In the relentless contest of hosts and viruses, this research signifies an important leap toward anticipating the viral evolutionary landscape, offering the tantalizing prospect of intervening not just in disease transmission but in the very genetic course of viral pathogens.
Subject of Research: Animals
Article Title: Host genotype and sex shape influenza evolution and defective viral genomes
News Publication Date: April 15, 2026
Web References:
References:
Costa, R., Potts, W., et al. (2026). Host genotype and sex shape influenza evolution and defective viral genomes. Nature Communications. DOI: 10.1038/s41467-026-71605-7
Keywords: Viruses, Evolutionary genetics, Virulence
