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 of hantavirus pulmonary syndrome (HPS), a rare infection spread by 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 rate," 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 internat
ional 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.
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."
Bullfrogs are a globally traded delicacy. Is that trade also spreading a deadly amphibian skin parasite, a phenomenon known as "pathogen pollution"?© Digital Vision
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.
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:
One risk factor for endangered mountain gorillas is common measles, spread by increasing tourism-based contact between apes and humans. Mountain gorillas share 97 percent of their genetic makeup with us, and are very susceptible to human diseases.© Digital Vision
"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.
Alonso Aguirre, director for conservation medicine at Wildlife Trust, specializes in the diseases of marine animals—some of which could make the leap to humans.© Wildlife Trust
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 Marlon 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 ("an 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 examp
les 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.