No Bird Flu Pandemic -- Yet
CDC 'Extremely Concerned,' but Killer Flu Still Not Spreading Among Humans
The vast majority of these human infections came directly from chickens or ducks. There's been one case of possible human-to-human transmission (the tragic case of a young mother who caught it after holding her dying child overnight). There may have been others, but there's been no ongoing bird flu spread among humans.
"The good news is these viruses have not yet acquired the ability to transmit from person to person in a sustained manner. The key word is sustained," Uyeki says. "There have been a few instances of limited person-to-person transmission. This highlights the potential for a pandemic in the future."
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.