Bird flu fears: How dire the threat?
MSN / Heatlh & Fitness / Special Guides / Bird Flu
Since 1997, bird flu has killed tens of millions of birds in several countries, and claimed the lives of dozens of people. Most people became sick through close contact with infected birds. But in a few instances, the H5N1 strain of the virus, which is uncommonly lethal, appears to have spread from person to person.
So far, the cases of human-to-human transmission have been rare and self-contained. But some experts fear that as the virus continues to mutate, it may produce a new, equally deadly strain that spreads easily among people, leading to a worldwide pandemic.
This troubling scenario has raised many questions. Here, James Steckelberg, M.D., an infectious disease specialist at Mayo Clinic, Rochester, Minn., answers some of them.
Worldwide epidemics (pandemics) of influenza aren't new; historically, they've occurred at approximately 25- to 30-year intervals and, like hurricanes and earthquakes, are natural events. Past pandemics have tended to occur when strains of influenza already present in animals adapt to human transmission.
Concern about the disease has intensified recently for several reasons. One is the appearance of several human cases of H5N1 influenza in regions previously unaffected by bird flu. Another is the news that researchers have determined that the 1918 flu pandemic, which killed 50 million people, was a bird flu that jumped to humans. And the H5N1 virus continues to spread among poultry in more and more countries.
The feeling among health officials and agencies worldwide is that it would be irresponsible not to be prepared, especially since we appear to be underprepared right now.
That's the question of the hour, and the truth is, no one knows. We do know a few important things about H5N1, the bird flu subtype that is the greatest cause for concern. First, H5N1 is particularly virulent, killing close to 100 percent of susceptible birds and more than half the people who have been infected. Second, the virus appears to be spreading, including most recently to Europe; it has now killed tens of millions of birds in a number of countries. Third, it seems to be affecting more and more species, including cats, which usually aren't susceptible to bird flu, and pigs, which traditionally have been a species that acts as a "mixing bowl" for viruses transmitted between birds and people. But whether this virus will ever make the genetic changes needed to infect humans on a mass scale, or how long that might take — there's just no way of knowing.
Right now, there's no evidence of sustained, efficient, human-to-human transmission. Most cases of bird flu in humans appear to have come from contact with infected birds, not infected people. When the virus has been passed from one person to another, such as was the case with a Vietnamese mother and daughter, the illness has been confined to close family members and doesn't seem to have spread to the wider community. This indicates that at least for now, the virus hasn't discovered how to effectively move from human to human.
If the virus mutates enough so that it spreads quickly among people, the great worry — and this wasn't true in 1918 — is modern transportation. Theoretically, infected people could board a plane and unwittingly carry the virus to the other side of the world in a matter of hours.
Is a Pandemic Similar to 1918 Likely?
Some of what's driving this concern is the historical perspective. An influenza pandemic occurs when a virus mutates so drastically from previous strains that people have little natural immunity, and so large numbers of people get sick or die. Flu pandemics typically occur about once every 30 years. Because the last pandemic took place in 1968, the thinking is that we're due for another one. And because there would be little natural immunity to H5N1, the effects could conceivably be devastating.
There's no commercially available vaccine as of yet, although prototypes that may offer some protection against the H5N1 strain are being studied. Once a specific vaccine is ready to go, it could take six to 12 months or more to produce meaningful supplies.
More readily available, and the primary treatment option right now, is the flu drug oseltamivir (Tamiflu), which may help limit symptoms and reduce chances the disease will spread. But it's not clear how effective this drug will be against bird flu. In Southeast Asia, H5N1 strains seem to have become resistant to it fairly quickly, and resistance to anti-flu drugs is growing worldwide. What's more, Tamiflu has to be taken within two days of the appearance of symptoms, which might prove logistically difficult on a worldwide scale, even if there were enough of the drug to go around.
Nevertheless, governments are stockpiling Tamiflu, but that doesn't mean that individuals should. For one thing, the drug is in short supply, and if there were a pandemic, it would be needed to treat infected people and help control the spread of the virus.
The 1918 strain was most lethal in adults in the prime of life, which means that pandemic strains may behave differently from the strains of flu that normally circulate. On the other hand, children seem very susceptible to bird flu, but that may be because they are more likely to have contact with infected birds or to play on ground contaminated with droppings. So far, people of all ages have contracted and died of bird flu.
The best thing to do is to take reasonable precautions. For instance, continue to get annual flu shots. They won't protect you from bird flu specifically, but they will reduce the risk of simultaneous infection with human and bird flu viruses — the main way that viruses swap genes, leading to new strains that can cause pandemics. Beyond that, the best protection is to wash your hands thoroughly and often and to avoid people who are sick or to stay home if you're sick yourself.
If you're traveling to areas where bird flu is prevalent, there are additional precautions you should take: Avoid rural areas, wild birds and open-air markets, and steer clear of ice cream and any other foods that contain raw or undercooked eggs because the shells may be contaminated with droppings.
Two good sources for factual information are the Web sites of the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO).
Last Updated: 10/14/2005
(c) 2005 Mayo Foundation for Medical Education and Research.
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