If you haven't given much thought to the bird flu in the past year, you aren't alone. While the spread of the dreaded H5N1 virus across Southeast Asia garnered much press coverage in 2005, the topic seemed to slip off the radar in 2006. Rest assured, however, the bird flu has not gone away. In fact, there were more cases of bird flu reported in 2006 than in any previous year. But the bulk of these cases appeared in the early months of the year, and international press turned its attention to other matters.
"One intriguing aspect of H5N1 is that countries that suffer it seem to shut up once a wave has passed. This time last year, Turkey was in paroxysms about H5N1. Now it's a non-subject. The same silence has fallen in Cambodia, China and Iraq," Crawford Kilian wrote in a recent email. Kilian, who teaches writing at Capilano College in Vancouver, Canada, maintains a website designed to aggregate information on H5N1. Traffic to the site was once as high as 1,000 visitors per day, but has dropped significantly as the issue's urgency has seemingly waned.
But experts continue to believe the world is closer to an influenza pandemic than at any other time since 1968.
"The evidence is still there. All I can say is we cannot let our guard down. We must maintain our vigilance," said Dr. Margaret Chan at her recent swearing-in ceremony as Director-General of the World Health Organization.
Chan cautioned that while there had been a lull in recent months, bird flu infections are on the rise. Last month, three Egyptians died as a result of H5N1 infection. Indeed, not a day after Chan's swearing-in, authorities in Hong Kong confirmed that a wild bird found dead in a busy shopping area was infected with the H5N1 virus.
Migratory birds have been carrying the H5N1 virus westward since its presence was first detected in Southeast Asia. It is believed that these birds act as reservoirs, or carriers of the influenza virus, and introduce a less-virulent strain of H5N1 to local poultry flocks. The virus then mutates into a highly pathogenic form. The deadliest strain of H5N1 spreads rapidly among poultry and is almost 100 percent fatal to chickens within 48 hours of infection.
"At some point, bird-to-bird H5N1 will break out again in most of the countries affected in the last 18 months—from Indonesia to Japan to Spain and Nigeria. It may persist as a poultry problem, or it may eventually mutate into a human-to-human form. How deadly it will be is very uncertain," Kilian said.
The first reported human case occurred in 1997. Since then, 261 people have been infected with H5N1 resulting in 157 deaths. The only thing preventing an H5N1 pandemic is that the virus does not currently exist in a form that is easily transmissible by humans. Most cases of human infection result from very close contact with infected birds.
In order for human-to-human transmission to occur, the virus needs to mutate in one of two ways. First, an exchange of genetic material between human and avian viruses could occur. This would cause a genetic reassortment of the virus that would transform H5N1 into an easily a transmissible human virus. If this were to happen, a surge of new illnesses would result as the reassorted virus suddenly found itself free to explore its new human playground.
Alternately, a gradual improvement in the virus' ability to bind itself to human cells could result in an easily transmissible human form of the virus. This would result in small clusters of human cases and a more measured spread of the disease.
U.S. researchers at the National Institutes of Health (NIH) recently began testing a new vaccine for use against H5N1. Instead of using a weakened strain of the virus to build up immunity, developers of the new vaccine are hoping to use "chunks" of DNA from the bird flu virus to prompt the human immune system to defend against H5N1.
A similar approach has yielded promising results with HIV/AIDS. Standard flu vaccine must be grown in hen eggs and takes six months to develop. H5N1 is 100% fatal to hen eggs.
Is the current lull in infections cause for concern? H5N1 could be in the process of mutating into a wilier, more virulent killer. Or it could be on the way out, going underground like SARS, or disappearing for good like the Black Death. No one knows for sure, but the smart money appears to be on the former likelihood, rather than the latter.
Kilian concluded: "SARS certainly gave us something to think about. But as with H5N1, one of the after-effects was amnesia."
Further Reading: Coverage of avian influenza by The New York Times.