For years, researchers have worried that H5N1 avian influenza would mix with human flu viruses, evolving into a form that keeps its current lethality but is far more contagious. That hasn’t happened — but the latest findings, published Feb. 22 in the Proceedings of the National Academy of Sciences, show how easily it might.
“Fortunately, the H5N1 viruses still lack the ability to transmit efficiently among humans.” However, this obstacle may be overcome by mixing with flu strains common in people, wrote researchers led by University of Wisconsin virologist Yoshihiro Kawaoka. “The next pandemic then will be inevitable.”
Current strains of H5N1 have infected 478 people since 2003, and killed 286 of them. It’s difficult to transmit in humans, requiring close contact with an infected person or animal. In birds, however, H5N1 is far more contagious, and his killed tens of millions of fowl. Cases have been concentrated in Africa and Eurasia, but as the swine flu pandemic demonstrated, any flu contagious to humans will likely go global, fast.
Influenza viruses swap genes easily, with co-infections turning animals into mobile petri dishes. In 2008, hoping to learn more about how H5N1 might evolve, researchers from the Centers for Disease Control and Prevention combined it with a common human flu strain. The hybrids proved less virulent than the original bird flu strain. Researchers wondered whether more contagious bird flu would necessarily always be less deadly in humans.
The PNAS findings suggest this may not be so. The researchers engineered all 254 possible variants of hybridization between a deadly bird flu strain found in Borneo, and a human flu virus from Tokyo. They identified three strains that, at least in mice, were both contagious and deadly.
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