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

E: The Environmental Magazine, Nov-Dec, 2004 by Jim Motavalli

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?"