Bird Flu Dies in Our Cold Noses

The H1N1 "swine flu" virus is spreading rapidly worldwide, but scientists have puzzled in recent years over why the H5N1 bird flu thus far has yet to do the same.

Now a new study blames our cold noses. Avian influenza viruses do not thrive in humans because the temperature inside a person's nose is too low, according to research published May 14 in the journal PLoS Pathogens.

Meanwhile here are the latest H5N1 bird flu stats from the World Health Organization: human cases have been reported in six countries, most of which are in Asia — Cambodia, China, Indonesia, Thailand, Turkey, and Vietnam. There are 424 lab-confirmed cases of bird flu, with 261 deaths worldwide. The first patients in the current outbreak, which were reported from Vietnam, developed symptoms in December 2003 but were not confirmed as H5N1 infection until early 2004.

Health officials initially warned that bird flu could become a pandemic. And it still could. It makes people very sick, but has yet to evolve to spread efficiently among humans. For comparison, the H1N1 flu is a near pandemic according to the WHO: As of early Friday, 34 countries have officially reported 7,520 cases. There are 4,298 lab-confirmed cases in the United States, including three deaths. Mexico has reported 2,446 lab-confirmed cases, with 60 deaths.

The new nasal study shows that normal avian influenza viruses do not spread extensively in cells at 32 degrees Celsius, the temperature inside the human nose. The researchers say this is probably because the viruses usually infect the guts of birds, which are warmer, at 40 degrees Celsius. This means that avian flu viruses that have not mutated are less likely to infect people, because the first site of infection in humans is usually the nose.

If given enough opportunities, the H5N1 bird flu virus will develop the characteristics it needs to start another influenza pandemic, the WHO states on its Web site.