TCS Daily

An Aging Epidemic

By Charles Murtaugh - August 16, 2002 12:00 AM

As if skin cancer and wildfires weren't enough to worry about, the past few years have given Americans a new summertime fear, one whose name conjures up the very dangers of the dark continent. In its characteristically cautious style, New Scientist recently warned that "West Nile virus will sweep across whole US," and National Review Online's John Derbyshire mentioned the virus in a gloomy column on the prospect of future "plagues". Even the chief of the Centers for Disease Control had described the virus as an emerging "epidemic".

When you look closer, though, West Nile appears a lot less scary. Since it first appeared in this country, in 1999, it has killed less than 30 people, while the flu kills 20,000 Americans every year. Also unlike the flu, West Nile virus is not communicable between people: it is spread by mosquitoes, but can only form a reservoir in birds. Since humans are a dead-end, rather than a host, West Nile is not subject to the sort of selective pressures that would enhance its virulence in humans. This may explain why only about one in ten infected individuals even feel ill, and fewer still seriously ill. Between its relatively low virulence, and its indirect mode of transmission, West Nile poses little threat of becoming an epidemic.

Does this mean that John Derbyshire is wrong to worry, and that infectious disease is a vanquished foe? Not necessarily. One thing that West Nile virus has in common with flu is that it is most dangerous to the elderly, and as America's population ages, it provides an increasingly target-rich environment to infectious disease.

Consider a fascinating paper published this spring in Science, documenting the steady increase in life expectancy that has occurred in the industrialized world over the past century. (Follow the link and you can read the full text, including the very provocative figures.) Contrary to almost innumerable predictions, the steady pace of this increase shows no sign of slackening. On this scale, even truly awful disease outbreaks such as the 1918 Spanish flu show up only as blips. But when this increase in life expectancy is combined with a decline in fertility, the result is the famous "graying" of the population that already worries Social Security reformers.

Perhaps unsurprisingly, the little news coverage that the Science paper received focused on its negative implications for pension programs. For pension program administrators, apparently, life can't be nasty, brutish and short enough; for the rest of us, the report ought to be rather cheering. For one thing, it casts some doubt on the oft-heard claim that we are choking ourselves on pollution, pesticides, and microwaves: if so, where's the impact on lifespan? (I see bad arguments on behalf of the environment the way Thomas Aquinas saw bad arguments on behalf of God: they do more harm than good, because they give unbelievers an opportunity to laugh.)

The authors of the Science report, Jim Oeppen and James Vaupel, are particularly struck by the smooth upward slope of the curve describing maximum average life expectancy across countries, which they describe as perhaps "the most remarkable regularity of mass endeavor ever observed." Much of that curve derives from advances that are unlikely to be reversed, such as improved nutrition and hygiene, and that contribute enormously to our societal residence to epidemics. As a species, humanity has reason to be proud of its success in postponing death, but it has contributed to a looming demographic irony: we are dying later, but more and more of us are dying every day.

When people get older, they tend to stop working: hence the looming Social Security crisis. They also, unfortunately, tend to die, and as the elderly make up increasing proportion of the population, so will the dying. Even if the rates of death due to infectious disease do not change, the result will be a net increase in the number of people dying of exotic and frightening diseases like West Nile virus or vancomycin-resistant bacteria, as well as of much more common killers like pneumonia or flu.

Could the result be a return to a simpler time when people faced death forthrightly, when death and the dying were central to social customs rather than shut behind closed doors? I rather doubt it. Instead, we are likely to be greeted with more and more hysterical coverage of exotic and rare bacterial and viral illnesses, each one deemed the latest threat to mankind's continued survival.

What will be the actual public health impact? The age bulge will put more buying power in the hands of senior citizens, who will spend it to combat their own ailments. This is all to the good: today, the lifespan trend is probably being driven more and more by investments in health care for the elderly. On the other hand, our long lives today owe much to childhood vaccine programs, established over the past century. If the vaccination network continues to fray, especially due to a misplaced public-health focus on rare but scary diseases like West Nile, such diseases will hardly be needed to fulfill John Derbyshire's worries. Measles and diphtheria can do the job nicely.



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