The resurgence of infectious diseases.

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 are disturbed.

An undisturbed ecosystem imposes a set of checks on the growth of microbes, but during severe disruptions, the balance may be skewed in their favor. The more disruption there is in the human habitat, the bigger the biological risks are for the people.

BIOLOGICAL MIXING

The environment in which the human species evolved and developed its basic defenses against disease was one that remained - despite natural disturbances - basically stable for thousands of years. In the past 100 years, it has changed radically - in forest cover, air and water quality, diet, and most recently in patterns of weather. The changes have boosted the spread of microbes, thereby increasing human vulnerability to infection.

The planet has become not only more vulnerable, but also - in effect - smaller and easier for small organisms to move around on. Surging growth in global tourism, migration, and trade has done the trick; distances that were once rarely covered within the life-span of a microbe are now covered routinely and easily, not just thanks to increased air travel but thanks to new roads cutting through wilderness areas. Microbes, which can hitch tides on anything from the boots of travelers to the wheel wells of planes, are extending their reach and coming into contact with more people.

One result is that viruses which previously remained hidden in remote rainforests suddenly have access to large human populations. Rapid settlement of the Amazon basin, for example, contributed to the spread of malaria-carrying mosquitos. The paving of the Kinshasa Highway across central Africa gave a fateful boost to the outbreak of AIDS. And the sheer volume of traffic between different ecosystems has brought about a process of planet-wide biological mixing. This mixing goes in both directions: mobility brings microbes to human populations, but human expansion also carries diseases into new areas. The bestselling book The Hot Zone, by Richard Preston, recounts how the deadly Ebola viruses were released from a remote African rainforest, as though the rainforest were a kind of Pandora's Box. According to Princeton University ecologist Andrew Dobson, however, what more often happens is that humans bring new vectors into the rainforest.

One reason the spread has been hard to stem is that these microbes are invisible stowaways, carried unwittingly by their hosts - and we have no way of knowing where the next outbreak will occur. Some changes in the environment may reduce the risk of disease transmission, while other factors will increase it. Changing agricultural practices can create new jobs and increase crop output, for example, but the changes may also invite new species to colonize. In any alteration of the landscape, there is potential for unforeseen consequences. After the Indira Gandhi Canal was built in Rajasthan, to irrigate desert-like areas of India, farmers switched from cultivating traditional crops of jowar and bajra to more commercially profitable wheat and cotton, which require large amounts of water. Large numbers of people came to the area in search of work. Then the monsoons came.

As it turned out, the main canal - 445 kilometers long, from Masitanwali to Ramgarh - served as an ideal breeding site for mosquitos. Instead of high crop productivity and prosperity, the heavy rains brought the farmers tragedy and death in the form of cerebral malaria, a parasite which is carried by Anopheles mosquitos. Excess rain, combined with water logging behind the canal and inadequate drainage in the fields, created an epidemic of malaria that quickly spread through extensive canal areas.

"The ignition wire of construction-related stagnant water, and the gunpowder of immigrant labor, created an explosion of malaria," reads a World Bank-commissioned report on India's Sardar Sarovar Dam Project. Malaria and water-borne diseases are common during the monsoon season, but the canals carried the malaria epidemic to a much larger area, exposing workers and farmers who then transmitted the disease to friends and families.

The dangers of irrigation projects are no worse than those of hydroelectric projects, road-building, logging, mining, and even urbanization. By displacing wild populations and habitats, development activities such as logging often deprive microbes of their usual hosts - in effect forcing them to find new ones. Essentially, this is what happened in 1975 with the Borrelia bacterium that causes a relapsing fever known as Lyme disease. The bacterium lives in four different tick species which spread it in their saliva - usually to deer and raccoons. But suburban development in Old Lyme, Connecticut, tended to substitute people for these other mammals in the disease cycle. Borrelia bacterium has since spread throughout the United States, and Lyme disease is rampant in New England and the upper midwest states of Wisconsin and Minnesota.

Along with the 100 to 200 microbes known to be dangerous, another 1,000 or more may be "out there," according to Paul Ewald, a biologist at Amherst College in Massachusetts. "It's a lottery" as to whether or not a pathogen will be introduced into the population. Understanding the various links between environmental disruption, microbial outbreaks, and health may be nearly impossible, but recognizing some general patterns will allow for better prediction and disease prevention. Four syndromes - water contamination, climate change, human actions that magnify natural disasters, and increasing social disruption - have been associated with such "unpredictable" occurrences as the Hanta and Gandhi Canal incidents.

BAD WATER

Many of the outbreaks have been linked to the degradation of natural systems, particularly of water. Infectious illnesses are widespread in areas with overburdened sanitation facilities and unsafe drinking water. Even in regions where water quality is considered fairly good, that impression is belied by the high levels of human waste and sewage carried in prominent rivers - the Danube, the Volga and the Mekong, among them - from which disease-carrying bacteria and viruses make their way into drinking supplies.

Waterborne diseases - including diarrheal diseases caused by E. coli, salmonella, vibrio cholera, and viral diseases such as hepatitis A and dysentery - cause hundreds of times more illness worldwide than chemical contamination of drinking water does. In 1992, 68 countries reported 461,783 cases of cholera and 8,072 deaths. In Russia, the very rivers that Russians depend on for life - the Volga, the Dvina, the Ob - are now hazardous to public health. The rivers harbor strains of cholera, typhoid, dysentery and viral hepatitis that spread through water systems and contaminate drinking supplies.

"Epidemic diarrheal diseases are both preventable and curable," says Dr. Ronald Waldman, former coordinator of the World Health Organization's Global Task Force on Cholera Control. "With a rapid and effective response, case-fatality rates from cholera, for example, can be kept to less than 1 percent. As health care professionals, we cannot allow a lack of preparedness to be responsible for an unnecessary loss of lives."

One method for predicting cholera may be detecting and monitoring plankton blooms. Rita Colwell, the University of Maryland biologist who is now President of the American Association for the Advancement of Science and Dr. Paul Epstein, of the Harvard School of Public Health, have studied the bacteria and viruses that catch a ride with plankton, and (with others) have shown that where there are blooms, there are corresponding outbreaks of diseases in humans, marine mammals and fish. In the late 1980s, toxic algal blooms and morbillivirus were associated with dolphin die-offs in the Mediterranean Sea.

Cholera, which comes from the Spanish word for anger, colera, erupts seasonally, when the temperature, sunlight, nutrient levels, and acidity are right for it. (At other times of year, the bacteria become dormant and hibernate with their plankton hosts.) During blooms, and in areas that have a history of waterborne illness, medical providers can curtail outbreaks by teaching residents how to diagnose cholera and how to avoid infection - by boiling water for drinking and washing food thoroughly.

In 1905, a new type of cholera was identified in the corpses of Moslem pilgrims who died at the El Tor quarantine camp en route to Mecca. The El Tor strain was more virulent than the classic strain of cholera because it proved to be a hardy survivor outside the human body, and the infection lasted longer in victims. By 1982, El Tor was the dominant strain in Bangladesh.

Even where there is a well-trained medical community, however, a seemingly minor event can sometimes trigger an epidemic. In 1991, for example, bilge water from a Chinese freighter was responsible for releasing this Asian strain of cholera into Peruvian waters. Once the bacterium of Vibrio cholerae OI, biotype El Tor, was released, it quickly spread through the marine environment and into drinking water supplies where it infected people. The bacterium also infected fish, mollusks, and crustaceans - which heightened the public health threat, because ceviche, raw fish with lemon juice, is an important local food. By 1993, there were more than 500,000 cases of cholera throughout Latin America, with 200,000 in Peru alone.

Given worldwide population growth and increasing pressures on scarce water supplies in many areas, the incidence of waterborne infections can be expected to keep rising, unless water quality protection is made a top priority in the planning and management of all water-using activities - from irrigation and hydropower to the disposal of sewage.

BAD WEATHER

Second, many outbreaks seem to be related to ongoing and incipient changes in climate. Warmer weather can expand the range of vectors: in July 1994, for example, 24 cases of malaria were reported in Houston, Texas, where warm weather had attracted malaria-infected mosquitos from Latin America.

Such conditions are likely to worsen before they improve. The Netherlands-based institute, Research for Man and the Environment (RIVM), reported last year that a global mean temperature increase of three degrees Celsius in the year 2100 increases the epidemic potential of mosquito populations in tropical regions two-fold and in temperate regions more than ten-fold. The RIVM model estimates an increase in malaria cases of several millions in the year 2100. And RIVM calculates that more than 1 million people could die each year as a result of "the impact of a human-induced climate change on malaria transmission" during the next 60 years - as many people as were killed in both World Wars. Yet, that would be the toll of just one disease among many. To address these threats, governments need to begin tracking the broad connections between their energy and transportation policies. Because these policies affect the rate of climate change, they can profoundly affect the long-term risks to public health.

HUMAN AMPLIFICATION

A third syndrome is that infectious outbreaks appear to follow on the heels of human activity that in some way magnifies the effects of natural disturbances - whether of floods, storms, or earthquakes. For example, some experts believe the outbreak of plague in Surat, India, in September 1994 was connected to the flooding of the Tapti River that summer, and an earthquake a year earlier. The quake had left the landscape devastated by ruin, and thousands of people homeless. Emergency aid and medical supplies were flown in for the survivors, but the effort was so successful that excess food had to be stored in warehouses, where rodents crawled in and feasted. The rodents reproduced quickly, allowing the pneumonic plague bacterium - harbored in the fleas that infest the rodents' fur - to greatly extend its range.

During the summer, the monsoon flooded the Tapti River and inundated the poorest districts of Surat with three meters of water. Again, people were forced to leave their homes. The rodents, too, were forced to seek shelter on drier land. Rats and people crowded together on the same high ground, increasing people's exposure to the plague bacterium. Although India was medically prepared to deal with water-borne diseases such as gastroenteritis, cholera and dengue fever, it had no plans for plague. The disease had not been seen in more than 40 years.

When the first cases were reported, more than one-third of the Surat's private physicians left town. Panic erupted as plague cases proliferated, overwhelming the medical system with fearful patients. Video footage showed victims being carted off in wheelbarrows, while families packed onto trains and roads to flee. All over the world, news reports warned travelers to stay away from India.

At Surat, a combination of weather patterns and earthquake and flood damage was exacerbated by social factors: shantytowns, squalid living conditions, warehoused food, inadequate health care, and panic fanned into hysteria by media coverage that focused on the disaster without explaining its causes. What could have been prevented or controlled at an early stage became a financial as well as social disaster, as international airline flights to and from India were canceled and trade came temporarily to a halt.

SOCIAL DISRUPTION

Finally, the vulnerabilities brought about by increasing environmental disruption and exposure are, in many ways, further amplified by the world's growing problem of internecine social disruption. With about 30 civil wars now taking place in the world, the systems needed for prevention and treatment of disease have been repeatedly shattered-often opening the way for infections to spread unchecked.

In Russia, health conditions are worsening because of the combination of unstable political conditions, deteriorating infrastructure, and the transitional economy. According to the head of the Russian Academy of Medical Sciences, as quoted in the 1992 Russian State Report on the State of Health of the Population of the Russian Federation, "we [Russia] have already doomed ourselves for the next 25 years."

Poor hygiene and diet, compounded by inadequate food supplies and high levels of pollution have brought an onslaught of ecological and human health problems to this part of the world. In the early months of 1994, Russians were hit by 22 percent more cases of tuberculosis than in the same months of 1993. Measles rose by 260 percent and mumps by 10 percent during the same period. In 1976, diphtheria had all but disappeared from the former Soviet Union thanks to childhood immunizations. But it surged back in the 1990s, rising from 1,200 cases in 1990 to 15,210 in 1993. The disease had come back everywhere, including Moscow and St. Petersburg.

Although it is a half-day's plane ride from Moscow, Russia's Pacific coast of Khabarovsk is not immune to the wave of infectious diseases that have swept across Russia since the collapse of the Soviet Union. People travelling to this mountainous coastal region have brought diphtheria with them. Meanwhile the mass exodus of refugees from southern regions of Russia has made it nearly impossible to stop the transmission of diseases that move directly from person to person.

Last summer, after recording nearly 1,000 cases of cholera, health officials in Dagestan, approximately 120 kilometers west of the Caspian Sea, imposed a quarantine to stop people from leaving the area. The quarantine was not successful at controlling the epidemic, since by then most people in the area were harboring the cholera bacterium whether they showed signs of it or not. In nearby Chechnya, all attempts at public health control have failed because of the war.

What has befallen Russia is echoed, in varying degrees, in India, in Latin America, and in the Four Corners area of the American Southwest. The paradigm is relentless: disrupted environments increase biological stresses on humans everywhere; mobility and population expansion increase their exposure to opportunistic microbes; and political or economic disruption prevent the application of known preventions or cures.

WRITING THE PRESCRIPTION

How this cycle can be broken is not something that can be determined by medical research alone. Enough research has already been done to yield the knowledge needed to control many of the epidemics spreading around the world: tuberculosis and malaria, for example. The problem is that the knowledge is not widely applied, and the diseases continue to spread.

Stopping the world's growing "epidemic of epidemics" may not be possible, in fact, until considerations of human health are integrated into all major human activities - including the planning of irrigation and dam projects, road building and transportation systems, agricultural practices, and extractive industries such as mining and logging.

In the future, along with keeping ecosystems intact and minimizing habitat alterations, communities should require planners to prepare for the unanticipated consequences of development. And they would do well to provide ongoing health education for their populations, especially in areas that are particularly vulnerable to environmental disruption.

Since infections do not stop at the borders of communities and countries, neither should control efforts. Individual nations need to coordinate with the World Health Organization and with each other to establish a reliable global surveillance system which would provide early warning, monitor incidence, and coordinate the response. Adequate medical supplies and complete treatment therapies can then be targeted to at-risk populations. Individual communities will need to adapt these programs to local conditions. In China, for example, the government set up a program to control schistosomiasis 40 years ago. At the national level, public health, water resources, agriculture, planning, and finance officials draft laws, plan programs and monitor progress. But it is up to leaders at the county and city levels - who know the local weather and terrain - to find and exterminate snails, educate their people, and treat the afflicted. The program is working.

When we begin routinely to take health impacts of our industries and societies into account, the outbreaks of disease that now shock us won't seem so puzzling. When the Hanta virus broke out in Arizona, for example, it was not as mystifying to some of the Navajo medicine men, whose traditions had taught them to see the interconnectedness of all living things, as it was to the medical specialists and the media.

The scientists, alerted that deer mice were carrying the problem, tested the mice and were able to identify the exact culprit. But they failed to notice that it was the environment that was changing, not the pathogens.

The Navajo medicine men meanwhile observed that prior to the outbreak, snow melt cascading down to the valley desert below, combined with a spring of heavy rains, had reminded some of their elders of the years 1918 and 1933, when there had been similarly unpredictable weather. In each of those years, there had been a disease. In each of those years, pinon trees produced an abundance of pine nuts. Mice had descended on the extraordinary harvest and reproduced ten-fold in one season. The rains had then forced the mice out of their flooded burrows to scurry about above ground, looking for food and shelter and increasing their exposure to humans. Disease was what happened when the balance of life was upset.

"When there is disharmony in the world, death follows," said one of the medicine men. He understood that when strange symptoms appear, they are not anomalies.

Anne Platt is a research associate at the Worldwatch Institute. Her article "Why Don't We Stop Tuberculosis?" (July/August 1994)was reprinted in the 1995 Project Censored Yearbook, Censored: The News That Didn't Make the News and Why.