H5N1 Difficult for Human Transmission, Scientists Say

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http://www.foxnews.com/story/0,2933,188792,00.html

 

H5N1 Difficult for Human Transmission, Scientists Say

Wednesday, March 22, 2006

 

OAS_AD('Frame1'); NEW YORK — Scientists say they've found a reason

bird flu isn't spreading easily from person to person: The virus concentrates

itself too deep in the respiratory tract to be spewed out by coughing and

sneezing.

But the virus could change that behavior by genetic mutation, taking a step

toward unleashing a worldwide outbreak of lethal flu.

Experts said the new finding doesn't indicate how likely such a pandemic is.

The virus may also need other mutations to take off in the human population,

they said. Still, the work suggests a particular sign to watch for in new virus

samples to help gauge the danger to humans.

The work, reported in Thursday's issue of the journal Nature, comes from

University of Wisconsin-Madison virologist Yoshihiro Kawaoka with colleagues in

Japan. Similar results, from the Erasmus Medical Center in Rotterdam, the

Netherlands, will be published online Thursday by the journal Science.

More than 180 people are known to have been infected with the bird flu virus

H5N1. Virtually all are believed to have caught it from infected poultry. But

scientists have long warned that the virus, which is prone to mutation, could

transform itself into a version that spreads easily from person to person. That

germ could touch off a pandemic.

Ordinary flu viruses spread when an infected person coughs or sneezes,

blasting out tiny droplets carrying the germ to others. For that to happen, the

virus has to be perched in the right places to be ejected by a cough or sneeze.

The new work suggests H5N1, by contrast, infects humans too low in the

respiratory tract for that to occur.

Both research teams used human tissue removed from various parts of the

respiratory tract — the region from the nose to the lung — to study where virus

infection occurs.

Scientists already knew that bird flu viruses use a specific kind of docking

site to enter cells they infect, while human flu viruses use a different one.

Kawaoka's group found the bird virus docking site appears mostly on lung cells,

while being rare on cells found in higher areas like the nose and windpipe.

Those higher areas were dominated instead by the human-type docking site.

Kawaoka said that for H5N1 to become a pandemic virus, it would have to mutate

in a way that lets it attach to the same docking site human viruses use. Other

mutations would be needed as well, he said in a statement.

Robert M. Krug of the University of Texas at Austin called Kawaoka's work an

important observation, and said that if H5N1 begins to use the human virus

docking site " we've got a lot to worry about. " It's not clear whether that would

be enough to produce a pandemic germ, he said.

James Paulson of the Scripps Research Institute in La Jolla, Calif., stressed

that other viral factors may be important in human-to-human transmission. But he

said that once the virus has a foothold in a person, regardless of where it is

in the respiratory tract, it may mutate to gain the abilities it needs to start

spreading among people.

 

 

 

 

 

 

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