Mutant Bird Flu Virus Evolves to Show Pandemic Characteristics

A mutant version of a bird flu virus created by scientists last year to show its ability to spread between humans evolved to show characteristics of previous pandemic viruses, a study found.

A genetic component of the mutant H5N1 virus developed a 200-fold preference for binding with human over avian receptors, according to a study led by researchers at the MRC National Institute for Medical Research in London. Their paper was published today in the scientific journal Nature.

The study builds on work led by Yoshihiro Kawaoka at the University of Wisconsin-Madison that showed how H5N1 could become highly transmissible if its hemagglutinin gene is mutated and mixed with those of the H1N1 virus that sparked the 2009 swine flu pandemic. As a follow-up, the MRC-led team plans to study the same binding properties of the current H7N9 virus reported in China, John Skehel, one of the study authors in London, said in a phone interview.

“The preference of the transmissible mutant for binding to human versus avian receptors, and the structural manner by which it binds them, are highly characteristic of pandemic viruses,” the researchers said in the published paper.

The hemagglutinin gene produces the protein that the virus uses to stick itself to host cells. By measuring the binding properties of the mutated gene in the H5N1 virus, the scientists found that its affinity for human receptors increased slightly, while its preference for avian receptors declined significantly, they said.

Binding Properties

Research published last year in the journal Science led by Ron Fouchier at Erasmus Medical Center in the Netherlands also found that five genetic tweaks made a strain of H5N1 spread more easily.

The new virus has genetic features of those that are known to jump easily from birds to mammals and a mutation that may help it attach to cells in the respiratory tract, Fouchier said earlier this month after reviewing a gene sequencing of H7N9.

As of April 23, 108 laboratory-confirmed cases of human infection with H7N9, including 22 deaths, have been reported by Chinese authorities, the World Health Organization said in a statement yesterday. So far, there is no evidence of ongoing human-to-human transmission, it said.

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