When a top World Health Organization official warned late last month that the bird flu virus that has plagued Asian countries might unleash a pandemic that could kill up to 50 million people, one thing that did not break out was mass panic.
After all, it's hardly the first time such a catastrophic prediction has been issued. Last year it was the SARS virus, now the potential mass killer is the H5N1 avian flu virus.
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While most health experts agree that the bird flu virus represents a grave danger and is highly likely to spread unless urgent steps are taken, some virologists caution that alarmist warnings could harm preparedness plans.
"The danger is that people might get blasé about the message," said Ian Jones, a virology professor at the University of Reading in England. "They'll think, Yeah, yeah, I've heard it before. It didn't come then, and it won't come this time."
Genetic Change
The H5N1 virus, a subtype of the avian influenza virus, is found in poultry. Scientists at first believed it was impossible for birds to directly infect humans with the virus. But an outbreak in Hong Kong in 1997 that killed 6 of 18 people infected with the virus proved the contrary.
Since then outbreaks have forced the slaughter of millions of chickens, ducks, and other birds across Asia. This year there have been 44 confirmed human cases of H5N1 flu in Thailand and Vietnam. Of these, 32 people died. There is not yet a vaccine for the disease.
Meanwhile the virus has undergone huge genetic changes and become even more pathogenic. It now affects not only birds, but also cats, pigs, and even tigers.
Experts fear the disease will mutate into a form that can leap between humans and sweep populations with no immunity. The adaptation could occur through a few genetic changes or what is known as "re-assortment" of the genes of the avian strain and the human strain. Domestic ducks and pigs are seen as likely transmitters.
"All virologists agree that this is a very dangerous time for H5N1," Jones said.
"Alarmist"
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