Playing chicken with the flu
If a bird can be the bearer of bad news, the dead duck found in China last week, felled by a highly pathogenic strain of avian flu called H5N1, brought a big chill to the world's public-health community. It marked the 10th and most populous Asian country to be hit by the bird illness in the past few weeks. The explosive emergence of this pathogen in so many different countries at once is unprecedented, according to the World Health Organization--and alarming. Already the disease has killed millions of chickens and led to the slaughter of many millions more in an attempt to contain it. More ominous, this bird flu has jumped the species barrier, infecting a minimum of 11 people and killing at least eight.
The real scare is that we could be watching a human flu pandemic in the making. Pandemics happen when a new and dangerous animal flu jumps to a human host, who has no immunity to the new strain, so it causes serious illness. The infected human in turn spreads the nasty virus to others. This last step--the spread from person to person--is what unleashes the disease's full fury. So far, humans infected with the H5N1 virus have not been contagious to others. But that could change overnight. And health authorities are scrambling to prepare.
Deadly mixture. If this dangerous strain keeps circulating in places where people live in the midst of roaming chickens and flying ducks, a highly contagious form may well evolve. The fear is that a person who is already infected with a garden-variety human flu will catch the deadly H5N1 avian form. Cohabiting in a human body, the avian and the human viruses can hook up and swap genes. Such intimacy could produce a new strain with just the right genes needed for easy person-to-person transmission. Obviously, keeping the bird flu away from humans is critical.
But at this point, culling infected bird flocks may not be enough. Once bird flu is entrenched, it's hard to get rid of. The virus is known to survive in water for four days and in manure for three months or more. And a single gram of manure can have enough virus to infect a million birds. Then there is the specter of migrating birds carrying the virus across borders--which some believe caused the poultry infection in the first place.
The bird flu is clearly out of the coop, and the rush is on to keep it from taking hold in humans. Adding to the urgency is evidence that our usual weapons against flu might not work well against an avian pandemic. Gene typing of the virus from one of the patients who died in Vietnam revealed a mutation that makes it resistant to two of the three antiviral drugs on the market, amantadine and rimantadine. That limits treatment options and puts pressure on the supplies of oseltamivir (Tamiflu), which does seem effective. Already, the Centers for Disease Control and Prevention is stockpiling this drug. Gene analysis also shows that our major defense against flu, a vaccine, would need serious modifications.
We have been making vaccine against each year's flu outbreaks the same way for over 60 years. A virus believed to be the best match for the one likely to be circulating in humans is grown in fertilized hens' eggs, then killed and turned into vaccine. "This way of making vaccines is archaic," says Adel Mahmoud, a physician and president of Merck Vaccines. And it would be cumbersome at best for the new avian flu. A mutation in the virus's coat has made it especially dangerous, and it would have to be genetically engineered to be less so before it could be grown in eggs. After that, clinical trials would be needed to see if the engineered vaccine still works, and at what dose, adding months to an already long process. The CDC, the Food and Drug Administration, and the National Institutes of Health are planning for this, but it's an open question whether an effective vaccine could be ready for mass use if the avian flu becomes a human threat.
So just as this year's flu season is winding down, the looming prospect of one far worse is teaching some hard lessons. As we confront the immediate threat, we should make a national commitment to develop flu vaccine technology fit for the 21st century, based on harmless viruses genetically engineered to stimulate immunity or even on designer proteins. The pandemic scare--whether it becomes reality or not--may be a needed wake-up call.
This story appears in the February 9, 2004 print edition of U.S. News & World Report.