Connecting the dots: the emerging science of conservation medicine links human and animal health with the environment.

Last June, Jeff Kaminski was a promising graduate student in Virginia Tech's Department of Fisheries and Wildlife Services, conducting field studies in Appalachia on the effects of logging on small mammal populations. In July, he was dead of acute respiratory distress, the victim on hantavirus pulmonary syndrome (HPS), a rare infection spread the exposure to the saliva, feces or urine of rodents.

HPS was unknown in the U.S. until 1993, when it erupted without warning in the Southwest. By late 2003, 353 cases had been reported. Thirty eight percent of the people infected died.

Why did HPS appear in 1993, and could our evolving climate be a factor? Dr. Eric Chivian and Sara Sullivan, both of the Center for Health and the Global Environment at Harvard Medical School, point to an unusual confluence of events in the Four Corners area, where New Mexico, Utah, Arizona and Colorado come together. A six-year drought, they report, ended that year with heavy snow and rainfall. The drought killed off owls, snakes, coyotes and foxes, natural predators of the native deer mouse, which then enjoyed a 10-fold population increase.

Many more deer mice increased the possibility of human exposure. "In this case," the scientists wrote, "a change in climate triggered the outbreak of a highly lethal infectious disease." And they added, "It is not known how many viruses or other infectious agents in the environment, potentially harmful to man, are being held in check by the natural regulation afforded by biodiversity."

In other words, the complex web of interlocking species, treasured by environmentalists but frequently disrupted by human activity, may be valuable for a whole new reason: Its delicate balance protects our health.

Vampire Bats: Silent Carriers

In 1998 and 1999, a previously unknown but murderous virus outbreak killed more than 100 people (40 percent of those infected) after showing up on the Leong Seng Nam pig farm in Malaysia. Horses, cats, dogs and goats were also infected with the virus, which was named "Nipah," after one of the villages affected. The virus soon spread to Singapore, sickening nine slaughterhouse workers who came into contact with Malaysian pigs.

Why did the specter of Nipah virus first make itself known on a remote pig farm in Malaysia? Scientists now say that the world's largest fruit bat, known locally as a flying fox, was the culprit. The pens that once held thousands of pigs are empty now, but still there are the large, overhanging mango and jackfruit trees that attract the bats. Could it be, scientists speculate, that the wholesale burning of millions of acres of forest in neighboring Borneo and Sumatra, destroying fruit trees, forced the increasingly endangered bats to look elsewhere for food?

It seems certain that the bats found a haven at Leong Seng Nam, that they were harboring Nipah virus, and that they then passed the virus on to the penned pigs (possibly by dropping half-eaten fruit). The pigs subsequently spread the virus to the farm workers who worked in close proximity.

The Palisades, New York-based Consortium for Conservation Medicine (CCM), a new coalition with a wide-ranging mandate, will test the environmental theory of Nipah virus spread with a four-year, $1.4 million grant from the National Institutes of Health. The grant is just one indicator that the scientific community is beginning to understand that some of our most serious health problems may have environmental roots.

CCM is a collaboration based at the Wildlife Trust that includes the Harvard Medical School, the Johns Hopkins Bloomberg School of Public Health, the federal National Wildlife Health Center and the Center for Conservation Medicine at Tufts. CCM's mission is to "strive to understand the link between anthropogenic environmental change, the health of all species, and the conservation of biodiversity."

Hantavirus in the U.S. and Nipah virus in Malaysia are different in many ways, but both bring together human health, animal health and environmental factors, the three interlocking circles of "conservation medicine." As reported in Environmental Health Perspectives, 19th century health-care practitioners were expected to have training in the natural sciences (as did Charles Darwin, making his pioneering work possible), but specialization in the 20th century drove the two fields apart. Today, doctors rarely talk to veterinarians, and neither has much interaction with wildlife biologists. Conservation medicine (some like the phrase "ecological medicine" better) is an attempt to bring them back together. The term "conservation medicine" was first used by M. Koch in a 1996 paper entitled "Wildlife, People and Development," and the field has grown dramatically since then.

The emerging field of conservation medicine carries with it a sense of urgency, prompted by a wholesale destruction of ecosystems that were still intact in Darwin's day. Diseases shared by humans and animals are called "zoonoses," and three quarters of all emerging diseases are zoonotic. "Diseases are moving from animals to humans and from one animal species to another at an alarming raw," says Lee Cera, a veterinarian at the Loyola University Stritch School of Medicine and a principal with the Conservation Center of Chicago. "When I went to school we were told, 'This disease won't go from a dog to a cat.' Then all of a sudden a dog virus decimated the lions of the Serengeti. How did it happen? When did it happen?"

Conservation medicine aims to answer these questions. It's an attempt to integrate complementary fields that had previously worked in isolation: human and veterinary medicine; infectious disease research; public health; and environmental science. Wildlife Trust, and its partner CCM, attempted to bring the parties together at a series of landmark conservation medicine symposia at Columbia University last July.

Parasitologist Peter Daszak, executive director of CCM, cites the West Nile Virus as an example of an emerging human disease transmitted from animal carriers, which is encouraged by greater international travel and commerce. There are many other examples: monkeypox, HIV, hantavirus, avian influenza (which in Thailand may now be moving from human to human), Marburg, Pfiesteria, Ebola and Lyme disease. SARS, for instance, was found in three species of wild animals tested in a marketplace in China. As USA Today described it, "As encounters between man, beast and the germs they carry increase, more strange new diseases can be expected to emerge."

At the heart of the problem are the same environmental issues that set up a conflict between development and ecosystem protection. Loss of animal habitat and increasing human incursion into wilderness areas (often spurred by human population growth) sets up new points of contact. International trade in exotic species breaks down previously existing barriers. Climate change causes species migration. Global travel, including ecotourism (which emphasizes wilderness visits) can move exotic jungle viruses into the modern world, as dramatically documented in Richard Preston's bestselling book The Hot Zone. In 1950, three million people a year flew on commercial jets; by 1990, 300 million did. Two million people cross international borders every day, carrying with them huge amounts of agricultural products, live animals, soil, ballast water--and disease-causing microbes.

In 1972, scientist Kent Campbell came down with a serious illness on a visit to Ireland. A senior scientist at the Centers for Disease Control, Thomas Monath, had discovered that rats carried the frightening and frequently lethal African microbial disease Lassa. The disease could be spread by airborne transmission, and Campbell was himself a victim of it. He survived (after being airlifted inside an airtight Apollo space capsule from London to Washington), and the world gained a new perspective on the ability of formerly exotic diseases to get a foothold in the modern world.

According to Louise Taylor of the U.K. Centre for Tropical Veterinary Medicine, 60 percent of all the 1,415 known species of infectious organisms that affect human health (causing a quarter of the world's deaths) can be transmitted by animals. Approximately 175 of these infectious organisms are linked to diseases that have only recently emerged, or have increased in severity (and geographic distribution) in recent years. There are 63 emerging diseases just among marine life, reports the book Conservation Medicine, and these include tuberculosis in fur seals and chlamydiosis in sea turtles.

Dying Frogs

Should we be alarmed by the worldwide disappearance of frogs? Are they an indicator species, a harbinger of global environmental crashes ahead? Jasper Carlton, director of the Biodiversity Legal Foundation, told High Country News that he believes that frogs and other amphibians are the proverbial canary in the coal mine. "Leopard frogs, boreal toads, spotted frogs and tiger salamanders are experiencing serious declines" he says. "We often attribute species decline to habitat destruction. What is particularly alarming is that many amphibians occupying undisturbed wilderness habitats are also disappearing at a previously unseen rate. These declines appear to be widespread and have been particularly serious for 20 years."

In 1993, environmental officials in Australia asked Rick Speare of James Cook University to help investigate the mysterious disappearance of upland frogs in Queensland. In this case, there was no shortage of evidence, because dead or dying frogs littered the O'Keefe Creek study area near Cooktown. Identifying the problem was of crucial importance, not least because the study area is the last known habitat of the sharp-snouted day frog.

The scientists benefited from the opportunity to make on-site pathological examination. Bacterial septicaemia was quickly ruled out, with the evidence pointing to a toxic or preacute viral cause. The only consistent lesions found on the specimens studied were heavy--but unfortunately unidentified--skin infections. Such infections had been observed before, but had been dismissed as related to minor parasites.

But further study, in part through a grant from Australia's Nature Conservation Agency, showed that this "minor" skin parasite was, in fact, the primary pathogen. The culprit was identified as an undescribed variation of the amphibian chytrid fungi, or chytridiomycosis. The chytrid has now been identified in 23 species of Australian frogs, seven of them endangered. This same parasite caused 100 percent mortality in a mass dieoff in Panama, and was also identified as a cause of mortality in frogs at the Washington Zoo. It has also been found in Africa and Europe.

What emerged was an international detective story. The parasite varies little from continent to continent, so evidence suggested it had recently migrated around the world. Enter the Consortium for Conservation Medicine.

Working with a National Science Foundation grant, the Consortium is investigating the possibility that the carrier is Rana catesbeiana, a bullfrog that is also a globally traded food item. While Rana is itself relatively resistant to chytridiomycosis, it may be an efficient carrier of it. The frogs of Australia (part of a pattern of declining amphibian populations around the world since the late 1890s) may be victims of what the Consortium calls "pathogen pollution," the anthropogenic introduction of non-native hosts or parasites to new locations.

Medical Hubris 

Laurie Garrett, author of The Coming Plague: Newly Emerging Diseases in a World Out of Balance, writes that in the postwar environment, powerful medical weaponry (antibiotics, vaccines, water treatment, anti-malaria drugs) gave scientists confidence that they could eradicate infectious disease from viral, bacterial or parasitical sources. In 1900, nearly 800 Americans out of every 100,000 died each year of infectious disease. By 1980, the number was down to 36 per 100,000. The Health for All accord, signed in 1978, set a goal of 2000 for eliminating many international scourges. But amid all this optimism, the numbers started rising. In 1995, 63 people per 100,000 died.

"The grandiose optimism rested on two false assumptions," Garrett wrote in the journal Foreign Affairs, "that microbes were biologically stationary targets, and that diseases could be geographically sequestered." Scientists, she said, "have witnessed an alarming mechanism of microbial adaptation and change ... Anything but stationary, microbes and the insects, rodents and other animals that transmit them are in a constant state of biological flux and evolution."

Conservation medicine is a realization that modern science is fighting a new kind of war, one that we're ill equipped to wage. Conservation medicine is still a very small field, but it is increasingly gaining recognition from mainstream funding sources, such as the National Science Foundation, the World Bank, the National Institutes of Health, and private grantmaking foundations. Ongoing studies are both uncovering new disease pathways (from animals to humans, and vice versa) and helping devise effective treatment. Here are some examples:

* RWANDA: The Volcano Veterinary Center was created in 1986 at the request of renowned mountain gorilla researcher Dian Fossey to provide emergency care to Rwanda's sick or injured gorilla population. One possible explanation for a high death rate among mountain gorillas noted in the late 1980s is an outbreak of measles. Mountain gorillas share 97 percent of their genetic makeup with humans, and are very susceptible to human diseases. Contact with them has increased exponentially as their fame has grown. Without question, their lives have been disrupted by human contact. Ecotourism is one avenue of contact, and the standards for tourists visiting the great apes are more relaxed than those for visitors to zoos or primate centers. The increasing human population (with a growth rate of 3.7 percent annually) in the region is also a threat. Gorillas have close encounters with trackers, guides, researchers and veterinarians, not to mention poachers and farmers. Bacteriological studies have shown the presence of salmonella, Cryptosporidium parvum, the parasite giardia and campylobacter among gorilla populations. Gorillas have become habituated to human presence, and "there is a concern that the habituation is enhancing transmission of pathogens infectious to both people and the gorillas," says parasitologist Thaddeus Graczyk of the Johns Hopkins Bloomberg School of Public Health, who also works with penguins that have been infected with avian malaria from North America.

* NEW ENGLAND: The alarming declines in common loon populations in New England are being studied by Dr. Mark Pokras of the Tufts Center for Conservation Medicine (CCM). Mercury poisoning is believed to be a cause. "The common loon serves as an important environmental sentinel for mercury because, like humans, it feeds on freshwater fish," Tufts CCM reports. The center has documented weight loss and death in common loons resulting from mercury poisoning, which comes from local sources and arrives via aerial transportation. The Wildlife Conservation Society reports that pending Bush administration proposals to relax standards on mercury emissions from coal-fired power plants could further adversely affect common loon populations (already declining precipitously) in the Adirondacks. "Models indicate that, partly due to mercury contamination, reproductive rates of loons may already be too low to maintain their populations in portions of Maine and eastern Canada," says David Evers of the Adirondack Cooperative Loon Program. Another result of human interaction is lead poisoning resulting from ingestion of fishing sinkers. Dr. Pokras has successfully influenced the Massachusetts Fish and Wildlife Agency to regulate lead sinkers in the Quabbin and Wachusett reservoirs, and they've been banned in New Hampshire and Maine.

* PERU: Researchers are making a link between destruction of the Amazonian rainforest and an explosion of malaria-bearing mosquitoes that thrive in sunlit ponds, according to a report in the journal Nature. A team from Johns Hopkins University collected 15,000 mosquitoes from a jungle road in northeastern Peru and counted how many were Anopheles darlingi, which transmits malaria. They then tabulated their results with statistics on deforestation using satellite images. An even one percent increase in deforestation increases the number of malaria-bearing mosquitoes by eight percent, says researcher Jonathan Patz. The study showed that the insects "ran wild" after 30 to 40 percent of the forest was destroyed. Malaria researcher Phil Lounibos of the University of Florida points out that the problem wouldn't be as acute if the A. darlingi mosquitoes hadn't been imported in the first place--a direct result of the establishment of tropical fish farms in Peru.

The Wildlife Trust: Emerging Leaders

Conservation medicine clearly needs a well-organized champion, able to synthesize the vast amounts of new scientific data from disparate sources. That work has fallen to the Wildlife Trust, which shares a leafy campus along the Hudson River in Palisades, New York with Columbia University's Lamont-Doherty Earth Observatory and CCM, whose work it fosters.

Wildlife Trust has a long history. The parent organization was founded in 1963 by British naturalist and author Gerald Durrell (brother of Lawrence Durrell, author of the "Alexandria Quartet" books). Mary Pearl, the executive director of Wildlife Trust, describes Durrell as "the Marion Perkins of England," with a wide following for his animal-themed books. Durrell became convinced that zoos had a responsibility to carry out conservation work, and to that end started breeding colonies of endangered animals at Jersey Zoological Park, which he founded. His work pioneered inter-zoo exchanges of animals and scientific information. Today, the British organization he founded continues as the Durrell Wildlife Conservation Trust, while the U.S.-based Wildlife Trust that developed from it (founded in 1971, and originally known as Wildlife Preservation Trust International) has undertaken a different mission.

There are many overlaps between the U.S. and British groups, however. The Durrell Trust has been active in attempting to restore critically endangered black lion tamarins (which live on just two percent of their historical forest habitat) to the wilds of Brazil. Three were reintroduced in 1999. The Wildlife Trust also works with black lion tamarins (and uses one on its logo), but its work concentrates on improving and connecting isolated pockets of tamarin habitat in Brazil.

The Wildlife Trust is not just the "go to" organization on conservation medicine; it virtually launched the discipline. The Trust conducts original research, bringing together teams of physicians, vets, ecologists, wildlife epidemiologists and public health officials to study the many strands of emerging diseases.

"We take a complex, multidisciplinary approach," says Pearl, who came to the Trust in 1994 from the Wildlife Conservation Society. "The stumbling block with many scientists is that they focus on pathogens in wild animals without considering the full environmental picture of how they got there."

The same problem exists with media accounts of disease outbreaks. Pearl points to a U.S. outbreak of monkeypox (a squirrel, rat and primate virus that can also affect humans) in the Midwest last year. Monkeypox is rare, and it usually occurs only in rainforests in central and western Africa. How did it get here? It turns out that pet traders in Wisconsin brought in an infected rainforest rat from Gambia. It infected the dealer's prairie dogs, which were then sold at a "pet swap" attended by people from other Midwestern states. Some of them got sick with a disease serious enough to kill 10 percent of those infected. The Centers for Disease Control and Prevention eventually confirmed 37 cases in five states.

It was a sensational story, treated as such by the media. "What the news stories don't tell you is that these disease outbreaks are predictable and therefore somewhat preventable," says Pearl. "But we have to systematically address the pathogen pollution that can occur in live animal markets, the exotic pet trade, unmonitored travel from outbreak areas and intensified livestock operations that reduce animal immunity to wildlife disease."

Alonso Aguirre, director for conservation medicine at Wildlife Trust (and both a veterinarian and wildlife biologist), specializes in the diseases of marine animals. He's seen pathogens that not only have the potential to wipe out critically endangered species (like the fibropapillomatosis tumors that increasingly infect green, loggerhead and olive ridley turtles), but also have the potential to move back and forth between unrelated animal species, and to infect humans. Aguirre cites seal populations with toxoplasmosis (a disease usually found in cats that can be a danger to pregnant women who change litter boxes); and Dutch seals with influenza B virus (identical to the human form that broke out in the Netherlands in 1995). Canine distemper has also infected both seals and dolphins in Western Europe and Russia. One theoretical method for human-seal transmission is marine mammal rehabilitation, which involves physical contact with possibly sick animals.

Aguirre notes that occurrence of the turtle tumors has been associated with such manmade phenomena as heavily polluted coastal areas, high human populations, agricultural runoff and biotoxin-producing algae. He has made a close study of endangered and declining Hawaiian monk seals, which have many challenges including human overfishing and a disease that causes blindness. The sight problem Can ocular condition of unknown etiology") was first noted in 12 female pups brought into captivity for rehabilitation purposes in 1995. "The blindness could have been caused by something human," Aguirre says. "It's possible our activity has introduced a pathogen."

Aguirre cites many such examples of diseases crossing species boundaries and international borders. "We should be very worried," he says, "because several diseases or pathogens have been linked to the wildlife and bushmeat trade, and to wildlife translocations worldwide." In addition to monkeypox, he cites SARS and new HIV-related viruses acquired through African consumption of wild-caught bushmeat. "In addition," he says, "we have ticks with Rift Valley fever carried in with tortoises imported from Africa, and exotic Newcastle disease introduced from the illegal bird trade, both turning up in California."

The solutions are potentially drastic, says Aguirre, who calls for increased enforcement and surveillance of the illegal wildlife trade, especially at airports. "It's a very difficult issue to tackle," he says, "because the trade is also tied in with drug and gun smuggling." He also calls for reform of international endangered species treaties (like the Convention on International Trade in Endangered Species of Wild Fauna and Flora, or CITES) and organizations (like the World Conservation Union) in areas where they have become "politicized, corrupted or inefficient."

Wildlife Trust casts a wide net, with projects ranging from sea turtle health assessments in Long Island Sound (part of a program on the New York bioscape) and manatee rehabilitation and evaluation in Florida to cattle impacts on tapirs in Argentina and flamingo health studies in Chile. Governed by a volunteer board, it has an annual budget of $5 million and an endowment of $6 million.

Front Line Research

The Wildlife Trust administers CCM, which conducts collaborative scientific research on emerging infectious diseases, pathogen pollution, climate change, the health of marine systems and problems affecting endangered species. CCM works with veterinary and medical students, promotes conservation medicine at workshops and conferences, and informs policymakers through Congressional briefings and other forums. CCM is studying West Nile virus through a seven-year, $557,000 contract from the New York State Department of Health. The Consortium is studying how the loss of bird biodiversity could produce high levels of West Nile infection, and also how carrier mosquito breeding is affected by local drought and flood cycles. It has worked to keep West Nile out of Hawaii, where it poses a dramatic threat.

Another CCM project is based in the Rocky Mountains, and studies interspecies disease transmission. Brucellosis, for instance, can move between elk, bison and cattle, resulting in controversial bison "roundups" when the animals stray out of Yellowstone Park. Other transmittable diseases include anthrax, affecting bison and livestock; rabies; whirling disease (present in trout in Yellowstone); and chronic wasting disease, which affects western deer and elk, bearing similarities to mad cow disease. Under the direction of Colin Gillin, CCM scientists are studying the possible effect of opening wildlife "corridors" on the health of livestock, wildlife and humans.

And, of course, CCM studies amphibian declines. Peter Daszak was a co-discoverer of chytridiomycosis, the fungal disease that is now associated with mass amphibian die-offs in Panama and Australia. "The fungus has been around for a long time," Daszak says. "It's found on amphibians in museums, and it blocks the way they breathe through their skin. But why did it suddenly spread to devastating effect? We started to see a pattern in the huge trade of amphibians for food, and for the pet trade. Bullfrogs, for instance, don't die from the infection but they spread it."

Monitoring how diseases spread is an important part of CCM's work. West Nile is a passenger in airplanes, says Daszak, and its spread is facilitated by dramatic increases in air travel. He describes a plausible scenario by which West Nile could reach Hawaii. There is an average of one and a half mosquitoes per flight, he says, and while only a tiny percentage are infected with West Nile, the law of averages suggests that a carrier will eventually make it off a plane and bite a bird. "And if a mosquito slips through, it will be only a matter of days before West Nile is all over the island," Daszak says, noting that avian malaria has already wiped out a third of the endemic bird species in Hawaii. (Native birds are surviving at high altitudes, above the reach of mosquitoes, but global warming is sending the biting bugs higher and higher each year.)

As part of its work, CCM has met with key health and military officials in Hawaii, and found them very supportive. "But it's a difficult agenda to push proactively," Daszak says. "If we're successful, nothing happens."

Environmental Factors

In most of the cases CCM studies, environmental factors play a huge role. Nowhere is this more true than with deadly Nipah virus, for which there is no known cure. Daszak says that the widespread deforestation in Sumatra, fueled by paper industry logging, eventually meant that fruit bats "ran out of resources. It's not enough to say, 'Let's eliminate fruit bats.' It's a much more complex situation than that." And now CCM's work has spread to Bangladesh, India and Madagascar, all of which harbor fruit bats and different strains of virus.

Sharon Collinge of the University of Colorado-Boulder studies incidence of bubonic plague (the same disease that killed a third of Europe's population in the 14th century)not in humans, but in prairie dogs. When it reaches a prairie dog colony, plague can kill 95 to 99 percent of its residents. Plague no longer kills humans quite as efficiently as it once did, because it is curable with antibiotics, but 10 to 20 cases still occur each year. Between 1957 and 2000, 48 plague cases were reported in the U.S. (nine of them fatal). In seven of those cases, prairie dogs were implicated as the carrier.

Collinge works in Boulder, which had a 14 percent human population rise between 1990 and 2000. The city's undeveloped growth boundary--an attempt to stop urban sprawl--hosts 218 prairie dog colonies, most of them in close proximity to human populations. The close quarters provide a possible pathway for plague to spread from "dogs" to humans.

Should people be alarmed? Collinge's team hasn't found plague in Boulder's prairie dogs, though outbreaks have occurred elsewhere. The gun-happy hunters profiled in our July/August issue cite their carrying disease as one reason to pull the trigger, but Collinge says that prairie dogs "are not good plague carriers, and getting rid of them would not stop the spread of disease" (which could be taken up by other small animals). Further, she says that prairie dogs are "both keystone species and ecosystem engineers," providing food for eagles and, through their burrowing, increasing the capacity of the soil to hold water and vegetation.

Collinge's work represents an ideal cross-pollination of medical and veterinary sciences. Dr. Pokras of Tufts University says such cross-boundary collaboration is exactly what's needed. "We need to get the vets out of the barn," he says. "We need to change the mindset of all the groups--vets, physicians, scientists, conservation biologists, environmentalists-to be more broadminded and visionary."

Pokras notes that the veterinary profession has always been driven by economic factors, first working on horses in the 1700s, then moving on to cattle, sheep, pigs and other economically important species in the 1800s. Pets came later, as people acquired the means to keep non-work animals. Only very recently have vets worked for zoos and nonprofit groups. "Starting in the early 1980s," Pokras says, "a variety of veterinary schools--including Tufts and Cornell--took big steps to get involved in conservation projects. But vets still mostly talk to their peers, and publish in their own journals."

One hurdle, Pokras says, is recognizing the skills of other professions, and learning to speak the same language. As noted in Conservation Medicine, the first book on the subject, "The rich terminology of the biomedical and veterinary sciences poses particular difficulties for ecologists and conservation biologists." For instance, even the word "ecosystem" has different meanings for the different interest groups.

"We see the world in a different way," Pokras says. "It's like the five blind men and the elephant. But we need to overcome this problem because conservation on a global scale is so complex that no one group has the knowledge, skills and perspective to grasp it all and develop appropriate solutions."

Weapons of Mouse Destruction

An 1860 painting by Gustave Corbet entitled "Fox in the Snow" provides a dramatic example of the age-old predator-prey relationship. The fox catches the squirrel, just as it has for centuries. But what happens when humans inadvertently disturb the balance of nature by removing the predators? The role of predators in helping suppress disease is highlighted in work by Richard Ostfeld of the nonprofit Institute of Ecosystem Studies (which combines research and education work). Mammals are the most common reservoirs of zoonotic disease, and rodents play the leading role, implicated in the spread of plague, Lyme disease, hantavirus and Rocky Mountain spotted fever.

"We know that predators affect prey numbers," Ostfeld says. "If mice are a zoonotic disease reservoir, and the human infection escalates with reservoir abundance, habitats that include foxes would have a lower incidence of disease."

In the case of Lyme disease, for example, a bacterial pathogen causes the disease to occur in white-footed mice, which then passes it on through blacklegged ticks. Without the predators that prey on mice, their population explodes and increases the chance that infected ticks will cause human Lyme infection. Ostfeld says the process of suburbanization, reducing forests to small fragments, increases risk because these parcels support fewer predators. "The risk of human exposure is four or five times higher in smaller forest fragments less than five acres than it is in larger parcels," he says. "That's where the weapons of mouse destruction come in."

Jeff Kaminski, the Virginia graduate student, was working with white-footed mice. "We're going to see more cases of that kind," Ostfeld says. "Rodents are resilient to human disturbances and they're reservoirs for pathogens that can attack people. As we encroach on and modify natural habitats, allowing rodent populations to explode, these outbreaks will increase. The evidence is very convincing that we're engaging in risky behavior. We need the political will to change how we modify the environment. I'm hopeful that we can stop habitat destruction, because if we reduce habitat fragmentation there's an immediate positive effect. Disease risk can be reduced in decades."

Few people would connect the loss of foxes and other predators to outbreaks of Lyme or West Nile, but that's exactly why conservation medicine is such an important new field. As Ostfeld notes, there are now tens of thousands of Lyme disease cases each year, but West Nile is catching up, spreading "at a phenomenal rate, several hundred miles per year. In five to 10 years it might surpass Lyme." And, according to the latest research (some of it as-yet unpublished), fragmentation and loss of biodiversity play a part in both diseases.

Addressing the Problem

A major report on changing ecosystems and their impact on human health is forthcoming from the Millennium Ecosystem Assessment, convened by the United Nations, in 2005. Also shedding light on conservation medicine is a new journal entitled EcoHealth.

The Tufts Center for Conservation Medicine is helping to create the Atlantic Coast-based Seabird Ecological Assessment. It is also part of an ambitious, multiyear research project called Yellowstone to Yukon (Y2Y) that is studying wildlife issues in the last tracts of wilderness in continental North America.

Columbia University's Earth Institute is using science and technology to assist public health efforts, through (among other tools) natural resource management and biodiversity preservation. Its Goddard Institute for Space Studies has examined the impact of global warming on urban environments, using New York City as a model. Cynthia Rosenzweig, a senior Goddard research scientist, says the alarming loss of wetlands in Jamaica Bay is in part due to global warming. "Our researchers realized that something was happening out there that went beyond the usual stresses on this highly manipulated ecosystem," Rosenzweig says.

The Global Fund is a multi-billion dollar international financing mechanism designed to help developing countries fight the infectious diseases AIDS, tuberculosis and malaria with practical initiatives. The Earth Institute's Center for Global Health and Economic Development is supporting the Global Fund through its Harlem-based Access Project, which helps developing countries apply for fund money, and then launches on-the-ground programs.

Josh Ruxin, an assistant professor of public health at Columbia, runs the Access Project, which has worked in such African countries as Ethiopia ($11 million in first-round funding), Nigeria ($28 million), Malawi ($42 million) and South Africa ($26 million). Devastated by AIDS and other plagues, many African countries have experienced a steep decline in life expectancy. In Zimbabwe, torn apart by both a political and public health crisis, life expectancy has plummeted more than 40 percent since 1990. In 2000, according to a UN report, the average Zimbabwean could expect to live to be 33.9 years old.

Ruxin, who started the Access Project during an earlier stint at Harvard, says that the state of public health pedagogy is antiquated and not suitable for the global health disasters we face today. I observed that there were no health systems in place, no money, and no good, management expertise to confront these modern scourges.

Ruxin points out that while the Global Fund has received $4 billion in global commitments, it has actually received only $1.8 billion from donor countries. The U.S. is part of the problem, he says, noting that President Bush has not lived up to the $15 billion commitment he made to fight AIDS around the world.

Both malaria and tuberculosis are on the list of diseases that confident postwar public health officials thought would be eradicated by 2000. Instead, they've become Third World scourges. Active tuberculosis cases can be treated with rounds of drug therapy if funding is available, says Ruxin, and prevention would make great strides if insecticide-treated bednets were universally available.

Awash Teklehaimanot is director of the Center for Global Health's malaria program and an internationally known expert on the mosquito-transmitted disease. Far from being eradicated, he says, malaria is now a threat to 40 percent of the world's population in 90 countries. There are 500 million clinical cases each year, and 2.7 million deaths. Most victims are children under five.

Malaria is at the center of conservation medicine controversies. Temperature is important for mosquito breeding, so populations can soar because of climate-induced warming. Rainfall creates the pools that mosquitoes breed in, and paradoxically so does drought (by drying up flowing rivers and leaving stagnant water).

An often-touted public health treatment for malaria is long-lasting DDT, the scourge of environmentalists since its role in ecosystem poisoning was exposed in Rachel Carson's Silent Spring. Teklehaimanot argues that DDT, if contained in low-volume localized indoor spraying, need not create environmental disasters. (Although banned in the U.S., it is still produced in Ethiopia and other countries.) Other aerosol insecticides last only a few hours; DDT, however, has a life of nine months to a year, making it a cost-effective treatment for underdeveloped countries.

"Malaria is a disease of poverty," says Teklehaimanot, "and this is one of the cheapest treatments available." In 1999, the World Wildlife Fund called for a global ban on DDT, claiming that up to 82 percent of the pesticide escapes into the environment. More recently, however, Teklehaimanot says WWF removed DDT from its list of 12 persistent organic pollutants presented at the Johannesburg summit, having designated it acceptable for certain public health uses. It has also been endorsed for that purpose by the World Health Organization (WHO).

Despite these signs of resurgence, however, DDT will remain a very controversial chemical. And this will be one more topic under discussion in the growing and increasingly important field of conservation medicine.

Public Health at a Crossroads

In her 2000 book Betrayal of Trust: The Collapse of Global Public Health, the aforementioned author Laurie Garrett outlines an international crisis, a complement to her earlier The Coming Plagues. She cites a partially classified 2000 CIA report that predicted widespread deterioration of global health. Its key indicators were "persistent poverty in much of the developing world, growing microbial resistance and a dearth of new replacement drugs, inadequate disease surveillance and control capacity, and the high prevalence and continued spread of major killers such as HIV/AIDS, tuberculosis and malaria."

A WHO report estimates that infectious disease causes 25 percent of global deaths. The present infrastructure is ill-equipped to handle this growing burden. As Garrett points out, WHO itself, "once the conscience of global health, lost its way in the 1990s. Demoralized, rife with rumors and corruption, and lacking in leadership, WHO foundered." Taking up the slack, she reports, was the World Bank, which became the world's largest public health funder by 1997.

But this is the same World Bank whose renewable energy portfolio is approximately $200 million per year, compared to the $2.5 billion it loans for other energy projects, most of them based around global warming-aggravating fossil fuels. These loans are very much a health issue. WHO estimates that 160,000 people die annually because of the effects of climate change.

Mark Walters, author of Six Modern Plagues and How We Are Causing Them, sees a "perfect storm of emerging disease." Humans, he says, "are animals, and we all share the same disease grid. No longer can we pretend that we're on some kind of pedestal above creation."

Walters asks, "How late are we in combating this avalanche of new diseases?" He traces successive waves of epidemics that began 10,000 years ago, when humans first domesticated animals. "Mutant cow viruses gave rise to smallpox," he says. "Measles developed from distemper, a virus in dogs. These animal-to-human exchanges caused wave after wave of major epidemics. But then it equilibrated, as people began to live with diseases. But civilizations built up, commerce developed, and populations began to mix, precipitating what may now be the fourth great wave of historical epidemics. And for the first time, we know why these epidemics are occurring."

Our growing medical knowledge, coupled with the relative stability of the Earth's ecosystems, led to centuries of improving human life expectancy and well being. But we're upsetting that stability and disrupting those ecosystems. "We're giving up the home court advantage, upsetting the evolutionary playing field," says Walters, whose work as a journalist and author is complimented with a veterinary degree. "Over the past century or more, humans have so disrupted the global environment and its natural cycles that we risk evicting ourselves from our shelter of relative ecological stability."

This kind of talk makes Waiters a Cassandra in the eyes of some conservative thinkers. National Review wrote that the book "resembles an age-old religious pronouncement--and a misguided one at that." Its sin? "Worshipping Mother Nature." The reviewer surveyed our progress in eradicating some former scourges, such as smallpox, and concluded, "Those suffering the most from disease epidemics need more trade and economic growth to escape from--not return to--the life of the primitive."

But victories with smallpox and other diseases are far from enough to get us to the goal so confidently outlined by the 1978 Health for All accord, which predicted a near-total victory over infectious disease by 2000. Researcher Jonathan Patz of the Johns Hopkins Bloomberg School of Public Health estimates that 2.5 million people are at risk from dengue fever infection, spread primarily by the Aedes aegypti mosquito, with between 250,000 and 500,000 cases of the most severe form occurring every year.

Malaria is an even deadlier scourge. And as Patz has written in his studies of the Northern Peruvian Amazon, a pattern of development, road construction and logging have resulted in a 50-fold increase in malaria cases. It's pretty simple, really. The destruction and clearing of ancient rainforests for development encourages mosquito breeding. And when those mosquitoes are infected with the emerging diseases we thought would be long gone by now, it makes people sick. CONTACT: Wildlife Trust, [phone], www.wildlifetrust.org.