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NATIONAL
Bird flu threat scares experts
By EDIE LAU
Sacramento Bee
March 09, 2005
- The flu this winter is still going around, but the buzz in the public health community is about next season's flu.
Word is, we could have a pandemic.
A pandemic is a disease that strikes many more people than usual in multiple countries. The flu circulates worldwide every year, of course, but a few particularly nasty versions of the virus are brewing in Asia.
The versions are called avian influenza because historically, they've infected birds, not people. Therein lies their danger.
"The (virus variety) will be one that we've never seen circulating in the human population, so we wouldn't have immunity to that," said Nicole Baumgarth, a University of California, Davis, immunologist who studies influenza.
"That's why people get so scared about it."
The fear is based on more than theory. Between Jan. 28, 2004, and Feb. 2 of this year, 42 of 55 people who contracted avian influenza in Asia died, according to a World Health Organization count.
Some individuals may be relatively resistant to the virus' effects: The WHO reported Tuesday it had tentatively identified seven people who were infected without becoming very ill. All the same, the death rate is very high for a flu bug. And the number of cases continues to grow.
Human infections have been detected in three countries: Vietnam, Thailand and Cambodia. With world travel as common as it is today, chances are high that the virus will spread.
"It's definitely going to come," Baumgarth said. "The thing is, how bad will it be?"
By nature, flu viruses are genetically unstable, constantly mutating. That's why the public health system comes out with new vaccines each year that it hopes match the variety of flu that is predicted to hit.
Because of the mutations, the possibility of an avian flu virus changing enough to infect humans is a constant threat, said Dr. Howard Backer, chief of the immunization branch and medical consultant for emergency preparedness at the California Department of Health Services.
But the strains circulating in Asia are of particular concern, Backer said, because:
- Culling chickens in affected areas, an act that contained past human outbreaks of avian flu, has not worked.
- The virus is highly lethal.
- Cats and pigs can become infected, too. The presence in pigs is especially worrisome, because for some reason, pigs are a good "mixing vessel" for flu genes, allowing a genetic shuffling that may produce dramatically new forms of the virus.
The one thing that keeps this flu from causing a pandemic now is that it doesn't spread easily from person to person. Health officials in this country aren't worried about Americans catching it from domestic chickens - assuming our fowl were infected - because livestock are housed much differently here.
Where the avian flu has popped up in humans, the people live in closer contact with their birds; for example, giving chickens the run of the back yard.
But if the virus mutates enough to begin transmitting easily among people, health officials fear the worst.
For those who've weathered many bouts of the flu, it may seem odd to think of the sickness as something that will kill you. Usually it doesn't, except in cases involving very young or very old people, or those with weak immune systems.
That's because most strains of the flu that infect people have been around a long time; at least some among us have developed some resistance to their effects.
Scientists who have examined influenza viruses under microscopes say they basically all look alike.
"In general, they're made out of the same genes and the same proteins," said Frederick Murphy, a University of California, Davis virologist and former director of the Center for Infectious Diseases at the national Centers for Disease Control and Prevention.
"They're about 100 nanometers in diameter," he said, referring to a measurement smaller than one one-millionth of an inch, "and they have an envelope with spikes sticking off the surface."
By themselves, viruses cannot reproduce. They need a "host," a cell of a living organism, to multiply.
The usual way people catch the flu is by inhaling viral particles in the air. The particles settle in the throat. Some of the spikes on the particle's surface, which protrude like upside-down bowling pins, enable it to latch onto and invade a cell.
Then the virus forces the cell to make more viruses.
Other spikes on its surface, which are shaped like mushrooms, enable a new particle to "bud off" from a hijacked cell. It goes on to infect another cell.
That's generally how a flu infection sets in, but how severe the infection will be, or whether the virus manages to infect at all, depends on the bug.