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No Bird Flu Pandemic -- Yet

CDC 'Extremely Concerned,' but Killer Flu Still Not Spreading Among Humans

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The longer bird flu viruses continue to spread among poultry, the greater the threat. The first time H5N1 raised its head -- in Hong Kong, in 1997 -- the slaughter of all the city's millions of chickens and a massive cleanup of live poultry markets eliminated the virus. But now the virus seems to have taken root in Southeast Asia -- not only among domestic chickens and ducks but in wild birds, too.

"The longer these viruses continue to circulate among poultry, it raises the potential for a [human] H5N1 pandemic, because of the capability of these viruses to evolve," Uyeki says.

And the direction of this evolution isn't reassuring, notes medical researcher Henry L. Niman, PhD, founder and president of Recombinomics, Inc.

"It's clear that the [H5N1] virus is evolving and getting a broad host range," Niman tells WebMD.

"We do know that these H5N1 viruses have been documented to transmit to a number of different animal species. That includes tigers and leopards and domestic cats," Uyeki says. "H5N1 is also confirmed to infect pigs in China; there have been a limited number of cases reported in pigs. The point is that these viruses are extremely concerning. They have transmitted to a number of animal species and have killed humans."

A recent report in the New England Journal of Medicine shows that human infection with H5N1 bird flu is more complicated than previously thought. The virus infected the brain and gut of two Vietnamese children who died with severe seizures and -- ominously -- severe diarrhea.

"The isolation of virus from a rectal specimen is a major source of concern, since it highlights a potential route of human-to-human transmission, especially in combination with crowded living conditions and diarrhea," Jenno D. de Jong, MD, and colleagues wrote.

The leader of this study, Jeremy Farrar, MD, PhD, is clearly worried.

"The great concern is there is an incredibly virulent avian flu that shows the ability to jump to humans," Farrar told WebMD in a December 2004 interview. "And when it gets to humans, it is clearly a very nasty disease with a high mortality rate."

In a recent assessment of the threat posed by a bird flu pandemic, the World Health Organization noted that this is the first time in history people have had any warning that a killer flu might be on the way.

"A pandemic may be imminent," writes WHO director-general Lee Jong-wook, MD. "This time, the world has an opportunity to defend itself against a virus with pandemic potential before it strikes."

CDC and WHO researchers already have identified viruses from which they can make a bird flu vaccine. Candidate vaccines are scheduled for testing at the National Institutes of Health. And Uyeki says that Vietnam is testing its own vaccine in animal studies.

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