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A Single Microbial Sea

Once upon a time, the developed world thought infectious diseases had been more or less wiped out by vaccines and antibiotics. But today we're battling AIDS and SARS and bird flu. And tomorrow we may be contending with contagions as yet unknown. What happened? And, more to the point, what can we do about it?

By Doug McInnis

Many of the great contagions of history still ravaged the globe's human inhabitants well into the 20th century. Smallpox killed millions each year. The 1918 flu epidemic left tens of millions dead.

Anyone, anywhere could be struck down. Wilbur Wright perished of typhoid nine years after he made aviation history at Kitty Hawk. Franklin Roosevelt, struck by polio in his late thirties, spent his presidency in a wheelchair. Tuberculosis (TB) killed residents of crowded cities and rural retreats alike. In 1901, if you had gathered 100 New Hampshire residents in a room, one of them, on average, could expect to die of tuberculosis within five years and 10 would be dead of TB before 1950. Yet by 1975, dramatic advances in medicine had made typhoid, polio, and tuberculosis increasingly rare. Even smallpox, which had killed more than 300 million people in the previous 100 years, was close to being eradicated, thanks to a global campaign mounted by the World Health Organization. Vaccines, antibiotics, and improved public health strategies had worked: the age of infectious disease seemed near its end, at least for the planet's prosperous nations.

Then came AIDS.

AIDS was the vanguard of a new group of emerging diseases that also now includes SARS, mad cow, avian influenza, and Ebola. These contagions joined antibiotic-resistant strains of tuberculosis and West Nile virus as increasingly worrisome threats to Europe and North America. Once, such diseases would likely have remained isolated in remote, undeveloped nations. But no place on Earth is remote in this age of global commerce and tourism.

"The one that brought this home to everybody was SARS," says Susan Dentzer, a 1977 Dartmouth College alumna who tracks global disease as the health correspondent for the PBS NewsHour with Jim Lehrer. "Even though it was highly localized in a few countries, there were nonetheless enough people who traveled from these countries that [there was] a serious impact on Canada. It was a miracle that nobody died in the U.S.



What do Singapore's harbor (top) and Sao Paulo's skyline (above) have to do with infectious diseases in the U.S.? Everything, say experts at Dartmouth and elsewhere—global trade, travel, and urbanization have changed the way we must look at contagions.

"The universal view of epidemiologists is that you can expect more outbreaks of new foreign diseases— it's only a matter of time," adds Dentzer, who is also a longtime member of Dartmouth Medical School's Board of Overseers.

"AIDS and SARS are prime examples of the fact that infectious disease is really a global phenomenon," agrees Fordham von Reyn, M.D., chief of infectious disease at Dartmouth-Hitchcock Medical Center. "This has a number of implications—first and foremost that control or even eradication of infectious diseases is now a global issue, not a local issue. Here at DHMC, we frequently see patients who've picked up diseases overseas. We see malaria, ulcerative skin disease, and numerous gastrointestinal infections. We also treat a number of people who acquired HIV in their country of origin.

"Global disease will be a constant threat," he maintains. "Microbes have the ability to develop resistance. New ones develop as the old ones are eradicated."

That all this poses a challenge for doctors and public-health experts goes without saying. But it also poses a conundrum for medical schools: How do you train medical students to recognize and treat diseases that don't yet exist? The short answer is that no medical school can do this, but they can train students to respond to the unexpected.

"We're stretching our students' skills for searching for answers to things that don't make sense," explains David Nierenberg, M.D., DMS's senior associate dean for medical education. "After all, when AIDS came along, it took doctors with the spirit of inquisitiveness to discover something they hadn't seen before. The greatest challenges are the diseases that exist that we don't know about. We encourage our students to read about them after they are discovered, or even discover them themselves." In fact, a graduate of DMS made a seminal contribution to the recognition of AIDS: the first report of a cluster of seemingly unexplained opportunistic infections in gay men in San Francisco came from Andrew Saxon, M.D., a 1970 graduate of Dartmouth Medical School.

Perhaps the great challenge is to control the rapid spread of diseases without shutting down the world's trade-based economy, which increasingly relies on air travel. "If you stopped air travel, it would stop the world's economy, which would lead to political instability, which can lead to disease," explains Paul Batalden, M.D., director of the leadership preventive medicine program at DMS. Such a drastic step, he states, "is not an option."

"When AIDS came along," says senior associate dean David Nierenberg, "it took doctors with the spirit of inquisitiveness to discover something they hadn't seen before. The greatest challenges are the diseases that exist that we don't know about."

At one time, North America's location—separated from Europe and Asia by two great oceans— usually provided a sufficient margin of safety. "In the past, the length of travel long exceeded the incubation periods for many infectious diseases," points out John Modlin, M.D., the chair of pediatrics at DMS and former head of the federal Advisory Committee on Immunization Practices. Those who were infected often either died aboard ship or were so obviously sick by the time they got here that they could be quarantined before entering the general population. "That's no longer the case with air travel," Modlin says.

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McInnis is a freelance writer based in Casper, Wyo., who specializes in science, agriculture, and business. His work has appeared in publications ranging from the New York Times to the Corn and Soybean Digest, from Harvard Magazine to the alumni magazine of Oberlin College, his alma mater.

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