Of birds and men
A deadly virus is brewing in Asia. Could this be the next killer pandemic?
Although the 2003 SARS outbreak is estimated to have cost the global economy at least $30 billion, most businesses have yet to consider the cost of a flu pandemic, both in terms of employee absenteeism and disruptions of the global economy. The CDC estimates the economic impact of a pandemic in the United States at between $71 billion and $167 billion, but those numbers don't include disruptions to commerce and society. "We've never suffered an event of such magnitude that it shuts down the global economy," says infectious-disease specialist Osterholm. "In 1918 we were much more self-sufficient."
SPREADING THE BIRD FLU
H5N1 avian flu virus has turned up in humans who contracted it from chickens or ducks. But many believe it will be only a matter of time before it spreads rapidly from person to person. There are four scenarios in which H5N1 could evolve to become more dangerous.
Scenario A
1 The host passes H5N1 to an intermediate host--a pig, for example.
2 A person passes a human strain of influenza A to the same intermediate host.
3 When both viruses infect the pig's cell, the genes from the H5N1 mix with genes from the human flu and create a new strain.
4 The new strain can spread from the intermediate host to humans.
[drawing labels]
Host (duck)
Human host
H5N1 strain
Human strain
Intermediate host (pig)
New strain
Scenario B
H5N1 infects an intermediate host. There, it undergoes small genetic changes that make it more efficient at infecting mammals. This strain then infects humans.
[drawing label]
Host
Scenario C
Without undergoing genetic change, H5N1 directly infects humans. Small mutations accumulate that let it spread quickly from human to human.
[drawing label]
Host
HOW H5N1 KILLS
How the virus kills people is not completely understood, but lack of exposure to H5N1 means that most people have no antibodies to fight it. Unchecked, it could spread with devastating effects on the body.
Encephalitis
Brain swells, possibly inducing coma and death. (1 known case)
Typical symptoms
high fevers
severe muscle and joint pain
respiratory infections
Flu weakens lungs, leaving damaged lining. Secondary bacterial infections can set in after the flu, causing pneumonia.
Immune system
The body mounts a strong reaction to H5N1 and overreleases cytokine, or chemical messengers, which tell immune cells to go to the lungs to fight the infection. When too many immune cells clog lung tissue, this "cytokine storm" damages the lungs, and the person suffocates.
Pneumonia
Infection or inflammation causes fluid buildup and impairs lung function. Infection spreading through the bloodstream can lead to death.
TRACKING THE VIRUS
So far, all known cases of H5N1 have been diagnosed in Asia. In the past year there have been 69 confirmed cases of the H5N1 virus; 46 of those infected, or 70 percent, died. Scientists are keeping a close watch on its spread, hoping to detect the first signs of a pandemic, or global flu outbreak.
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