Human Nose Too Cold for Bird Flu Virus

FRIDAY May 15, 2009 -- The inside of the human nose is a bit too chilly for the H5N1 avian flu virus, perhaps explaining why the strain has so far not spread easily between people, British and U.S. scientists reported Friday.

According to researchers from Imperial College London and the University of North Carolina, the avian flu virus thrives in the bird gut, where temperatures hover around 40 degrees Celsius (104 degrees Fahrenheit). In contrast, the inside of the human nose -- typically the first site of influenza infection for humans -- stays at about 32 degrees Celsius (89.6 degrees Fahrenheit).

Experiments suggest that avian flu strains cannot grow and replicate in this cooler environment, the researchers said, nor can they effectively kill nearby cells.

And when the team created a special mutant virus -- a human flu virus with proteins added from an avian flu strain -- this strain also struggled to survive and grow at 32 degrees C. This suggests that more than one mutation will be necessary for the H5N1 strain to become more at home in the human nose, the researchers said.

The findings are published May 15 in the journal PLoS Pathogens.

"Bird viruses are out there all the time, but they can only cause pandemics when they undergo certain changes," study co-author Wendy Barclay, of the division of investigative science, Imperial College London, said in a college news release. "Our study gives vital clues about what kinds of changes would be needed in order for them to mutate and infect humans, potentially helping us to identify which viruses could lead to a pandemic."

With that in mind, "animal viruses that spread well at low temperatures in these [cell] cultures could be more likely to cause the next pandemic," Barclay said.

The H5N1 avian flu virus is distinct from the current H1N1 swine flu virus, the focus of current pandemic fears.

More information

There's more on H5N1 avian influenza at the CDC.

Posted: May 2009


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