A new study has found that flu evolution within some individuals can hint at the virus’s eventual evolutionary course worldwide.
Samples taken more than 10 years ago from people with unusually long flu infections — and analyzed recently using modern genome sequencing methods — revealed certain viral changes that matched global flu evolution trends several years later.
The study, published Tuesday in the journal eLife, tracked how flu evolved over time in four people who were especially vulnerable to unusually severe viral infections: bone marrow transplant patients. For people with healthy immune systems, a typical flu infection lasts about a week, said Fred Hutchinson Cancer Research Center evolutionary biologist and doctoral student Katherine Xue, first author on the study. So she and her colleagues at the Hutch, Seattle Children’s Research Institute and the University of Washington studied viruses that originated from patients who received transplants and developed severe flu infections that lasted two or more months.
These four patients were drawn from a group of nearly 500 transplant recipients who participated in a previous study led by Fred Hutch infectious disease researcher Dr. Michael Boeckh, also a co-author on Tuesday’s study. That large study began in 2005 to improve understanding about the sometimes-devastating impact of respiratory viruses in this vulnerable population — in fact, two of the four patients whose samples were analyzed in the current study went on to die of their infections.
Knowing what the flu virus does in a single infected person is important, Xue said, but it’s difficult to study because the typical flu infection is so short. Most research tracks how the virus changes on a global rather than on an individual level.
“We know that flu changes really quickly from year to year,” said Xue, who is also a student in the University of Washington’s Genome Sciences Department. “All that evolution has to start somewhere. It has to start with individual mutations that arise within people while they’re sick.”