The resurgence of infectious diseases.

• Author: Platt, Anne

MORE THAN HALF A CENTURY AFTER THE DISCOVERY OF ANTIBIOTICS, INFECTIOUS DISEASES ARE ON THE RISE - WITH THE MOST DANGEROUS ONES NOW CARRIED BY SOME 2 BILLION PEOPLE. IN THE COMING YEARS, THE EPIDEMICS ARE ONLY LIKELY TO GET WORSE - UNLESS PUBLIC HEALTH CONSIDERATIONS ARE BROUGHT INTO THE FUTURE PLANNING OF ALL PUBLIC WORKS.

In May 1993, a physically fit 20-year-old Navajo Indian - a cross-country and track star - began gasping for air while driving to his wife's funeral near Gallup, New Mexico. For several hours, the man suffered from what seemed to be a severe but otherwise unremarkable case of the flu. Then, abruptly, his condition worsened. Blood filled his lungs. He was taken to an emergency room, where he died - drowning in his own serum. Reports confirm that around the same time, three other healthy Navajos in the Four Corners area (where New Mexico, Arizona, Colorado, and Utah meet) died from cases of flu or pneumonia gone suddenly awry. Clearly, something horrific was on the loose - but what?

Medical authorities from the state of New Mexico, the Indian Health Department, and the U.S. Centers for Disease Control and Prevention questioned families, relatives and friends, pored over medical records, and investigated possible links among the victims. They collected blood samples to analyze for viruses. Newspaper headlines warned cryptically of "Navajo flu," and "the mystery illness." As the death toll mounted, people in the affected region panicked, and some began to avoid anyone who was sick, for fear of contamination.

Investigation found that ground zero was a mouse - a rural deermouse, Peromyscus maniculatus, which is a native of most of North America, including the American southwest. Apparently, the deer mouse harbored a strain of the Hanta virus (named after the Hanta River in Korea where it was originally discovered), which causes severe damage to the pulmonary tract and lungs. It was not immediately clear, however, why this normally reclusive animal had suddenly begun to appear - and leave its droppings - in kitchens and playgrounds.

The press treated the Hanta outbreak of 1993 as an anomaly, a disturbing but isolated incident. In fact, however, it was part of a larger pattern that involves a growing list of illnesses - and growing risks to hundreds of millions of people. At the end of a century in which infectious diseases were thought to be well controlled, disease-causing (pathogenic) microorganisms are breaking out all over the world. Some of these pathogens, such as the Escherichia coli O157:H7 bacterium, Hepatitis C, and Rift Valley Fever are new and unfamiliar. Others are old ones we thought had been beaten, such as the microbes that cause tuberculosis, malaria, the plague, and measles.

AN EPIDEMIC OF EPIDEMICS

Despite the fact that most such afflictions are curable - and despite the major advances that have been made in sanitation, medical care, and increased public awareness of diseases and health in this century - infectious diseases still kill more people than cancer, or car accidents, or war. They kill more than 16.5 million people each year, and global incidence is on the rise.

Worldwide, 3.3 million people are killed by tuberculosis each year, while another 2 million die from malaria, predominantly in tropical regions. And for every person who dies, more than one hundred are infected. One-third of the world's people - some 1.8 billion - now carry the tubercle bacillus, the bacterium that causes tuberculosis. More than 500 million people are infected with tropical diseases such as malaria, sleeping sickness, river blindness and schistosomiasis.

As the 20th century approaches its end, changes of unprecedented magnitude and speed are taking place in the planet's physical and social environment, with the cumulative effect of allowing infections to spread far faster than anyone has been able to spread the means of preventing and treating them. The killing of forests, contamination of water, destabilization of climate, and explosion of urban population have all contributed to the weakening of public health protections. As a result, transmissions of infectious diseases through all media - air, water, insects, rats, and the human body itself - are on the rise.

Haunting these changes is an omnipresent biological pattern. As evolutionary biologists E. O. Wilson and others have observed, rapid disruption inevitably seems to favor some life forms over others.

This is a pattern seen at all levels, from microbes to mammals and from algae to trees. When a forest is burned, opportunistic, short-lived species spring up ahead of stable, long-term ones. When a building is bulldozed to an empty lot, weeds spring up before the return (if ever) of whatever species were there before. When coastal wetlands are disrupted to make room for resort hotels, algal blooms spread over the fragmented wetlands and choke them.

Among microbes, as among larger life forms, there are opportunistic varieties: bacteria or viruses that invade human blood or cells. Just as weeds exploit disturbance more quickly than slower-growing trees of a stable forest ecosystem, or insect pests exploit the reduced biodiversity of a crop, infectious agents can adapt fast enough to overwhelm societies whose "natural" environments...