Where Diseases Or Their Carriers Have Reached Higher Elevations

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Malaria

Highlands of Ethiopia, Rwanda,

Uganda and Zimbabwe Usamabara Mountains,Tanzania Highlands of Papua New Guinea and West Papua (Irian Jaya)

Dengue fever

San Jose,Costa Rica Taxco, Mexico

Aedes aegypti mosquitoes

(can spread dengue fever and yellow fever) Eastern Andes Mountains,

Colombia Northern highlands of India become all too familiar as the atmosphere heats up) favor the transmission of St. Louis encephalitis and other infections that cycle among birds, urban mosquitoes and humans.

This sequence seems to have abetted the surprise emergence of the West Nile virus in New York City last year. No one knows how this virus found its way into the U.S. But one reasonable explanation for its persistence and amplification here centers on the weather's effects on Culex pipiens mosquitoes, which accounted for the bulk of the transmission. These urban dwellers typically lay their eggs in damp basements, gutters, sewers and polluted pools of water.

The interaction between the weather, the mosquitoes and the virus probably went something like this: The mild winter of 1998-99 enabled many of the mosquitoes to survive into the spring, which arrived early. Drought in spring and summer concentrated nourishing organic matter in their breeding areas and simultaneously killed off mosquito predators, such as lacewings and ladybugs, that would otherwise have helped limit mosquito populations. Drought would also have led birds to congregate more, as they shared fewer and smaller watering holes, many of which were frequented, naturally, by mosquitoes.

Once mosquitoes acquired the virus, the heat wave that accompanied the drought would speed up viral maturation inside the insects. Consequently, as infected mosquitoes sought blood meals, they could spread the virus to birds at a rapid clip. As bird after bird became infected, so did more mosquitoes, which ultimately fanned out to infect human beings. Torrential rains toward the end of August provided new puddles for the breeding of C. pipiens and other mosquitoes, unleashing an added crop of potential virus carriers.

Like mosquitoes, other disease-conveying vectors tend to be "pests"—op-portunists that reproduce quickly and thrive under disturbed conditions unfavorable to species with more specialized needs. In the 1990s climate variability contributed to the appearance in humans of a new rodent-borne ailment: the hantavirus pulmonary syndrome, a highly lethal infection of the lungs. This infection can jump from animals to humans when people inhale viral particles hiding in the secretions and excretions of rodents. The sequential weather extremes that set the stage for the first human eruption, in the U.S. Southwest in

El Niño's Message

Scientists often gain insight into the workings of complicated systems by studying subsystems. In that spirit, investigators concerned about global warming's health effects are assessing outcomes "" of the El Niño/ Southern Oscillate (ENSO), a climate process that produces many of the same meteorological changes predicted for a warming world. The findings are not reassuring.

"El Niño" refers to an oceanic phenomenon that materializes every five years or so in the tropical Pacific. The ocean off Peru becomes unusually warm and stays that way for months before returning to normal or going to a cold extreme (La Niña). The name "Southern Oscillation" refers to atmospheric changes that happen in tandem with the Pacific's shifts to warmer or cooler conditions.

During an El Niño,evaporation from the heated eastern Pacific can lead to abnormally heavy rains in parts of South America and Africa; meanwhile other areas of South America and Africa and parts of Southeast Asia and Australia suffer droughts.Atmospheric pressure changes over the tropical Pacific also have ripple effects throughout the globe, generally yielding milder winters in some northern regions and parts of Southeast Asia and Australia suffer droughts.Atmospheric pressure changes over the tropical Pacific also have ripple effects throughout the globe, generally yielding milder winters in some northern regions

Nino Weather Africa

Disease Outbreaks Accompanying Extreme Weather during the 1997-98 El Niño

Extreme Weather

Abnormally wet areas

Abnormally dry areas

Disease Outbreaks Accompanying Extreme Weather during the 1997-98 El Niño

Extreme Weather

Abnormally wet areas

Abnormally dry areas

1993, were long-lasting drought interrupted by intense rains.

First, a regional drought helped to reduce the pool of animals that prey on rodents—raptors (owls, eagles, prairie falcons, red-tailed hawks and kestrels), coyotes and snakes. Then, as drought yielded to unusually heavy rains early in 1993, the rodents found a bounty of food, in the form of grasshoppers and pinon nuts. The resulting population explosion enabled a virus that had been either inactive or isolated in a small group to take hold in many rodents. When drought returned in summer, the animals sought food in human dwellings and brought the disease to people. By fall 1993, rodent numbers had fallen, and the outbreak abated.

Subsequent episodes of hantavirus pulmonary syndrome in the U.S. have been limited, in part because early-warning systems now indicate when rodent-control efforts have to be stepped up and because people have learned to be more careful about avoiding the animals' droppings. But the disease has appeared in Latin America, where some ominous evidence suggests that it may be passed from one person to another.

As the natural ending of the first han-tavirus episode demonstrates, ecosystems can usually survive occasional extremes. They are even strengthened by seasonal changes in weather conditions, because the species that live in changeable climates have to evolve an ability to cope with a broad range of conditions. But long-lasting extremes and very wide fluctuations in weather can overwhelm ecosystem resilience. (Persistent ocean heating, for instance, is menacing coral reef systems, and drought-driven forest fires are threatening forest habitats.) And ecosystem upheaval is one of the most profound ways in which climate change can affect human health. Pest control is one of nature's underappreci-

of the U.S. and western Canada. During a La Niña, weather patterns in the affected areas may go to opposite extremes.

The incidence of vector-borne and waterborne diseases climbs during El Niño and La

Niña years,especially in areas hit by floods or droughts. Long-term studies in Colombia, Venezuela, India and Pakistan reveal,for instance, that malaria surges in the wake of El Niños. And my colleagues and I at Harvard of the U.S. and western Canada. During a La Niña, weather patterns in the affected areas may go to opposite extremes.

The incidence of vector-borne and waterborne diseases climbs during El Niño and La

Niña years,especially in areas hit by floods or droughts. Long-term studies in Colombia, Venezuela, India and Pakistan reveal,for instance, that malaria surges in the wake of El Niños. And my colleagues and I at Harvard

Nino Map Health Hantavirus Dengue

Mosquito-borne:

Disease Outbreaks

Dengue fever Rodent-borne: Hantavirus pulmonary syndrome ^ Encephalitis Waterborne: 6 Cholera

Malaria Noninfectious: O Respiratory illness resulting

& Rift Valley fever from fire and smoke

Mosquito-borne:

Disease Outbreaks

Dengue fever Rodent-borne: Hantavirus pulmonary syndrome ^ Encephalitis Waterborne: 6 Cholera

Malaria Noninfectious: O Respiratory illness resulting

& Rift Valley fever from fire and smoke

University have shown that regions stricken by flooding or drought during the El Niño of 1997-98 (the strongest of the century) often had to contend as well with a convergence of diseases borne by mosquitoes, rodents and water (map). Additionally, in many dry areas, fires raged out of control, polluting the air for miles around. ENSO is not merely a warning of troubles to come; it is likely to be an engine for those troubles. Several climate models predict that as the atmosphere and oceans heat up,El Niños themselves will become more common and severe—which means that the weather disasters they produce and the diseases they promote could become more prevalent as well.

Indeed, the ENSO pattern has already ^ begun to change. Since 1976 the intensity, duration and

O pace of El Niños have ■a increased. And during the 1990s, every year was marked by an El Niño or La Niña extreme. Those trends bode ill for human health in the 21st century.

ated services to people; well-functioning ecosystems that include diverse species help to keep nuisance organisms in check. If increased warming and weather extremes result in more ecosystem disturbance, that disruption may foster the growth of opportunist populations and enhance the spread of disease.

Unhealthy Water

Beyond exacerbating the vector-borne illnesses mentioned above, global warming will probably elevate the incidence of waterborne diseases, including cholera (a cause of severe diarrhea). Warming itself can contribute to the change, as can a heightened frequency and extent of droughts and floods. It may seem strange that droughts would favor waterborne disease, but they can wipe out supplies of safe drinking water and concentrate contaminants that might otherwise remain dilute. Further, the lack of clean water during a drought interferes with good hygiene and safe re-hydration of those who have lost large amounts of water because of diarrhea or fever.

Floods favor waterborne ills in different ways. They wash sewage and other sources of pathogens (such as Cryptosporidium) into supplies of drinking water. They also flush fertilizer into water supplies. Fertilizer and sewage can each combine with warmed water to trigger expansive blooms of harmful algae. Some of these blooms are directly toxic to humans who inhale their vapors; others contaminate fish and shellfish, which, when eaten, sicken the consumers. Recent discoveries have revealed that algal blooms can threaten human health in yet another way. As they grow bigger, they support the proliferation of various pathogens, among them Vibrio cholerae, the causative agent of cholera.

Drenching rains brought by a warmed

Indian Ocean to the Horn of Africa in 1997 and 1998 offer an example of how people will be affected as global warming spawns added flooding. The downpours set off epidemics of cholera as well as two mosquito-borne infections: malaria and Rift Valley fever (a flulike disease that can be lethal to livestock and people alike).

To the west, Hurricane Mitch stalled over Central America in October 1998 for three days. Fueled by a heated Caribbean, the storm unleashed torrents that killed at least 11,000 people. But that was only the beginning of its havoc. In the aftermath, Honduras reported thousands of cases of cholera, malaria and dengue fever. Beginning in February of this year, unprecedented rains and a series of cyclones inundated large parts of southern Africa. Floods in Mozambique and Madagascar killed hundreds, displaced thousands and spread both cholera and malaria. Such events can also greatly retard economic development, and its accompanying public health benefits, in affected areas for years.

Solutions

The health toll taken by global warming will depend to a large extent on the steps taken to prepare for the dangers. The ideal defensive strate gy would have multiple components.

One would include improved surveillance systems that would promptly spot the emergence or resurgence of infectious diseases or the vectors that carry them. Discovery could quickly trigger measures to control vector proliferation without harming the environment, to advise the public about self-protection, to provide vaccines (when available) for at-risk populations and to deliver prompt treatments.

This past spring, efforts to limit the West Nile virus in the northeastern U.S. followed this model. On seeing that the virus had survived the winter, public health officials warned people to clear their yards of receptacles that can hold stagnant water favorable to mosquito breeding. They also introduced fish that

Weather and the West Nile Virus

This diagram offers a possible explanation for how a warming trend and sequential weather extremes helped the West Nile virus to establish itself in the New York City area

MILD WINTER

Weather and the West Nile Virus

MILD WINTER

Weather Extremes Mosquitoes

eat mosquito larvae into catch basins and put insecticide pellets into sewers.

Sadly, however, comprehensive surveillance plans are not yet realistic in much of the world. And even when vaccines or effective treatments exist, many regions have no means of obtaining and distributing them. Providing these preventive measures and treatments should be a global priority.

A second component would focus on predicting when cli-matological and other environmental conditions could become conducive to disease outbreaks, so that the risks could be minimized. If climate models indicate that floods are likely in a given region, officials might stock shelters with extra supplies. Or if satellite images and sampling of coastal waters indicate that algal blooms related to cholera outbreaks are beginning, officials could warn people to filter contaminated water and could advise medical facilities to arrange for additional staff, beds and treatment supplies.

Research reported in 1999 illustrates the benefits of satellite monitoring. It showed that satellite images detecting heated water in two specific ocean regions and lush vegetation in the Horn of Africa can predict outbreaks of Rift Valley fever in the Horn five months in advance. If such assessments led to vaccination campaigns in animals, they could potentially forestall epidemics in both livestock and people.

A third component of the strategy would attack global warming itself. Hu

Livestock Vaccination Africa

SATELLITE IMAGE revealed that the sea-surface temperature of both the western equatorial Indian Ocean and the eastern Pacific was warm (boxes) and that the Horn of Africa was lush with vegetation (green) because of heavy rains. This pattern indicated that the Horn was at risk for an epidemic of Rift Valley fever in livestock and people. Satellite surveillance is being used increasingly to detect conditions conducive to disease outbreaks, so that preventive measures can be taken.

SATELLITE IMAGE revealed that the sea-surface temperature of both the western equatorial Indian Ocean and the eastern Pacific was warm (boxes) and that the Horn of Africa was lush with vegetation (green) because of heavy rains. This pattern indicated that the Horn was at risk for an epidemic of Rift Valley fever in livestock and people. Satellite surveillance is being used increasingly to detect conditions conducive to disease outbreaks, so that preventive measures can be taken.

man activities that contribute to the heating or that exacerbate its effects must be limited. Little doubt remains that burning fossil fuels for energy is playing a significant role in global warming, by spewing carbon dioxide and other heat-absorbing, or "greenhouse," gases into the air. Cleaner energy sources must be put to use quickly and broadly, both in the energy-guzzling industrial world and in developing nations, which cannot be expected to cut back on their energy use. (Providing sanitation, housing, food, refrigeration and indoor fires for cooking takes energy, as do the pumping and purification of water and the desalination of seawater for irrigation.) In parallel, forests and wetlands need to be restored, to absorb carbon dioxide and floodwaters and to filter contaminants before they reach water supplies.

The world's leaders, if they are wise, will make it their business to find a way to pay for these solutions. Climate, ecological systems and society can all recoup after stress, but only if they are not exposed to prolonged challenge or to one disruption after another. The Intergovernmental Panel on Climate Change, established by the United Nations, calculates that halting the ongoing rise in atmospheric concentrations of greenhouse gases will require a whopping 60 to 70 percent reduction in emissions.

I worry that effective corrective measures will not be instituted soon enough. Climate does not necessarily change gradually. The multiple factors that are now destabilizing the global climate system could cause it to jump abruptly out of its current state. At any time, the world could suddenly become much hotter or even much colder. Such a sudden, catastrophic change is the ultimate health risk—one that must be avoided at all costs. E9

The Author

Further Information

PAUL R. EPSTEIN, an M.D. trained in tropical public health, is associate director of the Center for Health and the Global Environment at Harvard Medical School. He has served in medical, teaching and research capacities in Africa, Asia and Latin America and has worked with the Intergovernmental Panel on Climate Change, the National Oceanic and Atmospheric Administration, and the National Aeronautics and Space Administration to assess the health effects of climate change and to develop health applications for climate forecasting and remote-sensing technologies.

The Emergence of New Disease. Richard Levins, Tamara Auerbuch, Uwe Brinkmann, Irina Eckardt, Paul R. Epstein, Tim Ford, Najwa Makhoul, Christina dePossas, Charles Puccia, Andrew Spielman and Mary E. Wilson in American Scientist, Vol. 82, No. 1, pages 52-60; January/ February 1994.

Climate Change and Human Health. Edited by Anthony J. McMichael, Andrew Haines, Rudolf Slooff and Sari Kovats. World Health Organization, World Meteorological Organization, United Nations Environmental Program, 1996.

The Regional Impacts of Climate Change: An Assessment of Vulnerability, 1997. Edited by R. T. Watson, M. C. Zinyowera and R. H. Moss. Cambridge University Press, 1997. Summary from the Intergovernmental Panel on Climate Change available at www.ipcc.ch/pub/ reports.htm

Biological and Physical Signs of Climate Change: Focus on Mosquito-Borne Diseases. Paul R. Epstein, Henry F. Diaz, Scott Elias, Georg Grabherr, Nicholas E. Graham, Willem J. M. Martens, Ellen Mosley-Thompson and Joel Susskind in Bulletin of the American Meteorological Society, Vol. 79, pages 409-417; 1998.

Other Web sites of interest: www.heatisonline.org and www.med.harvard.edu/chge

Form from Fire

Self-propagating heat waves can engender new and improved materials, but only recently have researchers found ways to monitor these ultraquick chemical reactions by Arvind Varma

Think of a burning trail of gunpowder. The fire races along its length, leaving nothing behind except loose ash and gases. Now imagine igniting the end of a different trail of powder. This time the bright, glowing wave of heat that surges through the mixture leaves a solidified mass in its wake. This seemingly paradoxical effect—that burning need not always use up materials or break them down—is entirely real and is the essence of one of the most promising innovations in materials science: combustion synthesis.

Scientists have known about combustion synthesis for three decades, and they have learned to create more than 500 compounds, many of which have proved to be invaluable as ball bearings, nuclear safety shields, abrasives, high-temperature superconductors and other technologically advanced items [see box on page 61 ]. But despite this long history, trial and error has been the primary means of invention. For example, a researcher might eventually realize that starting with finer powders can make the synthesized material stronger, but he or she could only guess at the reasons why. As a result, the applications of combustion synthesis have remained highly specialized. Only recently have engineers begun to understand how a heat wave actually propagates through the original mixture, leaving the desired material in its wake. Knowing precisely what happens between starting components and final product is the best way for researchers to refine techniques of combustion synthesis for widespread use.

Since prehistoric times human beings have been burning things for advantageous ends. About 13,000 years ago people discovered that baking a piece of malleable clay transformed it into hard ceramic. Modern technologists have learned how to fire special clay powders in a furnace to produce ceramic shields that are strong and heat-resistant enough to protect spacecraft. In both cases, the process applies external heat to break the chemical bonds of the original material and to rearrange them into a new structure.

When scientists observed in the late 19th century that shuffling chemical bonds can release significant heat energy, they began to wonder whether it might be possible to use this energy directly to synthesize useful materials. In 1972 scientists in the former Soviet Union discovered how to harness enough of this energy to drive a synthesis reaction without continuing to heat the mixture. Thus, combustion synthesis not only makes a new solid from disparate starting components, it also self-propagates—once heat is applied to start the reaction, it runs on its own. And all it takes to ignite a combustion-synthesis reaction is a brief heat pulse from sources such as a tungsten coil or a laser beam, which use significantly less energy than do industrial furnaces, the most common method for creating advanced materials.

Saving energy is just one of many advantages that combustion synthesis holds over conventional techniques of materials production. The energy-consuming nature and size of furnaces limit the volume of material that can be converted. Combustion synthesis can yield objects of virtually any size,

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