MONDAY, Feb. 6, 2006 (HealthDay News) -- Researchers have identified several different genetic strains of the avian flu virus, H5N1, in different bird populations in Southeast Asia -- any one of which could trigger a pandemic.
The finding has implications for preparations against a possible pandemic and the vaccines that may be needed to ward off human infection, experts say.
One key recommendation: Better surveillance of bird populations to make sure one of the H5N1 variants doesn't begin to spread more easily between people.
"There are multiple different lineages of H5N1 emerging in the world," said lead researcher Robert Webster, a professor of virology at St. Jude Children's Research Hospital, in Memphis, Tenn., and a member of the Department of Microbiology at the University of Hong Kong. "There are about four different families of viruses out there now."
His team's report appears in this week's edition of the Proceedings of the National Academy of Sciences.
The threat of a mutant strain of deadly H5N1 that could pass easily from person-to-person has raised fears of a worldwide pandemic. Since January 2004, at least 152 laboratory-confirmed cases of bird-to-human infection have been reported to the World Health Organization, and 85 people have died from the disease.
So far, however, the virus appears to lack the ability to jump easily from human to human, experts say.
In the study, Webster's team found that the H5N1 virus exists frequently in domesticated poultry populations and also in wild birds before they migrate. Using genetic analysis, the researchers found four distinct sub-lineages of the virus existing in birds from different geographical areas.
While H5N1 can be transmitted over long distances in migratory birds, in Southeast Asia infected poultry appears to be the main way H5N1 is spread, Webster's team noted.
"These viruses can be out there in apparently healthy birds all the time," Webster said. "These viruses are not killing all the chickens [that carry them], so they are out there," he added.
The spread of myriad genetic types of H5N1 highlights the need for a variety of vaccines, Webster said.
"Multiple, different vaccines are going to have to be prepared and held ready in case one of these goes human-to-human," he said. "It will be necessary to have vaccines to each one of them." Based on evidence from the bird-to-human cases recorded so far, "there is human infection in all the types," he added.
Webster believes that more genetic types of the virus will develop. "Whether one of these will become pandemic, God only knows," he said. "It looks as if it could be. So it behooves us to get our ducks in a row and be prepared. It's scary."
One expert thinks the variety of virus types is a good argument for overhauling America's vaccine production system.
"There is a lot of genetic variability in H5N1," noted Dr. Marc Siegel, a clinical associate professor of medicine at New York University School of Medicine, and author of Bird Flu: Everything You Need to Know About the Next Pandemic. "This is not surprising."
Siegel believes the ability of the virus to change should be a major concern for vaccine developers. "It's another wake-up call that we need a vaccine system where we can turn it around quickly," he said. "We don't need nine-month lead times. We have the technology to make vaccines quickly."
H5N1 may still not become pandemic, Siegel stressed. "That's a speculation whether it's going to be H5N1 or something else," he said. "Eventually, there is going to be another pandemic."
The key point about H5N1 is that it is a deadly virus to which people have no immunity, Siegel said. "That's a good reason to be concerned and keep tracking it," he said. "The knowledge that there are more subtypes out there is a very good reason to update how we make vaccines."
He added that the first priority should be to control the virus in birds.
"There should be more vaccination of birds," he said. "We need a rational approach to this. A rational approach means a greater attempt to control it in birds -- put the fire out rather than build the firewall."
More information
For more on avian flu, visit the U.S. Centers for Disease Control and Prevention.
