The major uncertainty is whether the relevant bird flu virus, H5N1, which is already devastating flocks in Asia and Europe, will mutate into a form that has a similarly devastating effect on humans. Right now, bird flu can kill humans under rare circumstances, such as when people are in close, frequent contact with raw duck blood, or other conditions highly unusual in developed countries and unusual even in undeveloped ones that increase the odds of transmission from birds to humans.
But to devastate human populations in the way that it has bird populations, H5N1 would have to mutate into a form that spreads easily between and among humans rather than just from birds to humans. Currently it does not appear to spread from human to human, and several changes would have to occur in the genetic code of H5N1 for it to do so.
In the meantime, though every death is tragic, bird flu has taken a relatively small toll in human lives. The World Health Organization has reported a total of 175 known cases of human infection with H5N1, all among people working in close contact with infected domesticated birds. Of those, 95 have died.
Compared to the daily toll from smoking, car crashes, or countless other killers, those numbers are minuscule but there are a few important reasons that we cannot heave a sigh of relief:
Roughly 54 percent of those humans who have become infected
with H5N1 have died, a disturbingly high fatality rate that
may not bode well if the disease begins spreading rapidly
The infamous flu pandemic of 1918-1919, which killed tens of
millions of people around the world, is believed to have
originated as a bird flu a reminder that we are especially
susceptible to diseases that do not normally occur in mammals
and to which we therefore have little immunity.
It is difficult to prepare in advance for a possible bird flu
pandemic, because we wouldnt know the exact nature of the
virus were fighting until the dreaded mutations occurred that
made it easily transmissible between humans.
Despite all these reasons for concern,
defensive measures are being taken: research into new antiviral
drugs possibly one that target parts of the viruss genetic code
unlikely to alter as it mutates; the development of faster
production methods for churning out a vaccine if a pandemic occurs;
and the stockpiling of Tamiflu and Relenza, existing antivirals that
may help reduce the severity of symptoms for those who catch bird
flu, though their likely efficacy is a subject of debate.
While our best hope is that the feared mutations to H5N1 simply never occur, it is wise to be prepared for the small but real possibility, given what history teaches us about the potential magnitude of such a pandemic. At ACSH, we strongly and frequently advise against wasting resources on minimal or purely speculative threats, but this is one case where the consequences might be devastating enough to make a heavy investment now reasonable.
As of the end of February, human cases of bird flu were believed limited to southeast Asia, Turkey and Iraq. In bird populations, though, the disease had quickly spread to South Korea, Vietnam, Japan, Thailand, Cambodia, Laos, Indonesia, China, Malaysia, Russia, Kazakhstan, Mongolia, Turkey, Romania, Croatia, Ukraine, Iraq, Nigeria, Azerbaijan, Bulgaria, Greece, Italy, Slovenia, Iran, Austria, Germany, Egypt, India, France, Hungary, Bosnia-Herzegovina, Switzerland, Georgia, and Niger.
If it reaches the United States and in birds, at least, it likely will it is likely to appear first on the West Coast, coming over among migratory birds from Asia to Alaska. Again, its appearance in birds alone, or in very rare bird-to-human cases, is not reason to panic or even to be surprised. If and when mutations allowing human-to-human transmission occur, it will still not be appropriate to panic. But it will time to face a potentially devastating crisis with level-headed resolve and the best and most technologically advanced public health resources we can muster.
Elizabeth Whelan, Sc.D., MPH, is president of the American Council on Science and Health and serves as an adviser to theBusiness & Media Institute. ACSH has just published the report Avian Influenza, or Bird Flu: What You Need to Know. Visit ACSH www.acsh.org  or Health Facts and Fears www.healthfactsandfears.com 
for more information.