Connecting the Dots (Continued)

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.

© Wildlife Trust

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 r

elationship. 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 bed nets 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 Walters 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.