UW-Madison scientist solves bird flu puzzler
DAVID WAHLBERG [email protected]
March 22, 2006A UW-Madison researcher has an answer to a bird flu question that has stumped scientists: Since the virus is powerful enough to kill many of the people it infects, why doesn't it spread easily among people as the regular flu does?
The answer, according to virologist Yoshihiro Kawaoka: Cells in the upper part of people's respiratory tracts, where coughing and sneezing readily transmit germs, have very few bird flu virus receptors - but many human flu virus receptors.
Cells in the lower part of the respiratory tract, which includes the lungs, have plenty of both kinds of receptors, Kawaoka found. That explains why many of the people infected with the H5N1 bird flu virus have developed deadly pneumonia in their lungs, even though they haven't infected others, he said.
"This gives the scientific reason why the H5N1 viruses are not easily transmitted," said Kawaoka, who reports on the research in today's edition of the journal Nature. "It lays the foundation for the identification of important changes that may occur in the virus."
Before the H5N1 virus can cause a human pandemic, the new findings suggest, it must mutate and become able to recognize human flu virus receptors, Kawaoka said.
The virus, which has led to the death or slaughter of millions of birds in Asia, Africa and Europe, has killed 103 of the 184 people known to be infected since 2003, nearly all of them thought to be sickened by birds.
If the virus starts spreading from person to person, health officials say, it could cause a pandemic like the one in 1918 that killed up to 50 million people worldwide.
"We don't know how many more mutations are required," Kawaoka said. "But at this point, we still have some time."
The findings should help scientists identify dangerous changes to look for in the virus, he said. But the research won't enable better drug or vaccine development because no new vulnerabilities in the virus were identified.
Kawaoka, who last week was named head of the $9 million Institute for Influenza Viral Research to open next year at University Research Park, has published several studies about bird flu in recent months in prominent journals.
He revealed that a bird flu sample from Vietnam was resistant to the drug Tamiflu; he refined a "reverse genetics" technique he helped develop to make flu vaccine production more efficient; and he showed how flu viruses organize their genetic material to create infectious particles.
In the latest study, Kawaoka worked with colleagues at UW- Madison and the University of Tokyo in Japan. They analyzed normal tissue samples from the respiratory tracts of Japanese lung cancer patients whose tumors were surgically removed.
Many bird flu virus receptors were found in all samples taken from the lungs of eight patients, Kawaoka said. In all samples taken from the nasal cavities and bronchial tubes of three patients, very few bird virus receptors were found.
Scientists had previously known that the bird flu virus receptors were present in some respiratory tissues, but they didn't know the distribution among different kinds of cells within the respiratory tract, Kawaoka said.
The large gap found in the number of the bird flu virus receptors between cells in the upper and lower respiratory tract surprised even Kawaoka. "It's so clear cut," he said.
Though the study involved tissue from only a small number of Japanese patients, Kawaoka said the findings apply to the general human population because the results were so clear and the patients weren't related.