The human influenza virus H1N1 that caused the 2009 flu pandemic, and H9N2, an avian influenza virus that is endemic in bird populations in Asia, are close cousins—close enough that they can swap genes if they find themselves in the same cell, resulting in new viruses that are a patchwork of the parent strains. Scientists suspect that some gene combinations may result in a particularly potent form of flu and ignite a pandemic in humans. But because these viruses are more likely to meet in the lungs of an Asian chicken farmer than under the nose of a virologist, researchers find it difficult to predict which gene combinations might be the most virulent and contagious.
So instead of waiting and seeing, researchers have played matchmaker and thrust the two viruses together in a test tube. A team in China generated 127 hybrid viruses and injected each one into lab mice. More than half of the hybrids were as good as their parent strains at infecting the mice, and eight of them proved to be more pathogenic, the team led by Jinhua Liu of the China Agricultural University in Beijing reports online today in theProceedings of the National Academy of Sciences.
"These are important experiments", says virologist Peter Palese of Mount Sinai Medical Center in New York City, who was not involved in the work. The viral hybrids that the Chinese team has identified are the ones that scientists might want to watch out for worldwide, he says. If these strains were recognized early, governments could launch a speedier response.
Creating highly virulent viruses in the lab is controversial, says virologist Ab Osterhaus of the Erasmus University Medical Center in Rotterdam, the Netherlands. "[But] I don't think we should shy away from these experiments. ... The more information we have, the better," he says.
He explains, however, that the hybrids that are the most virulent in mice will not necessarily be the most dangerous in humans, nor the most contagious. "Mice mirror, to a certain extent, what happens in humans," he says, but they are not perfect model animals. Liu agrees. He plans to investigate how contagious his new viral blends are in guinea pigs and ferrets—animals whose respiratory system better reflects our own feverish battle with flu.