During the early stages of a pandemic, viruses tend to evolve in ways that enhance their ability to reproduce and spread, rather than to evade the host’s immune system. The genetics and sex of the host influence how a novel virus adapts to a new environment, but scientists don’t fully understand how these factors work individually or together.
New research on mice led by University of Utah biologists sheds fresh light on this mystery by demonstrating that some hosts appear to serve as “evolutionary accelerators” that could enable viruses to gain virulence more quickly.
“Some hosts seem to select for virulence-associated mutations, virulence traits that affect other hosts as well. This supports the idea that if a virus infects them, then it’ll become worse for the entire population. We don’t know this yet, but it’s what our work indicates that could be happening,” said Rodrigo Costa, a postdoctoral researcher in the U’s School of Biological Sciences. That gain in virulence appears to occur more quickly in female mice of a specific strain.
Costa is the lead author of the National Institutes of Health-funded study that appears in Nature Communications.
Do more resistant hosts help accelerate virus virulence?
This study shows that both host genetics and sex deeply influence how influenza viruses evolve. Host-driven effects could help explain why some viruses become more dangerous in certain populations as they evolve. Understanding these patterns could help public health officials model outbreaks and design control strategies.
The research also underscores the power of experimental evolution of pathogens to reveal how they attack and circumvent host defenses, according to principal investigator Wayne Potts, a U professor of biology.
“These revelations are often unpredictable. For example, when we designed these experiments, our favored hypothesis was that increased viral genetic diversity–via inoculations of viruses collected and mixed from multiple infected hosts—would be a major factor influencing virulence evolution, something we also tested,” Potts said. “There was some support for this hypothesis, but it was minor compared to the influence of host sex and genotype and the observation that more resistant hosts select for greater viral virulence.”
The team’s experiments discovered that when the virus infects a naïve host, it retains its virulence from the previous host encounters, a relatively novel finding which implies that there could be specific hosts that act as ‘evolutionary accelerators.’
“If we found that this is also true in humans, then in the future, with enough sequencing data and more knowledge of these interactions and what these proteins do, maybe we can predict which hosts will be more likely to make the virus more virulent and immunize those people first,” Costa said.