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

"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 And, according to the latest research (some of it as-yet unpublished), fragmentation and loss of biodiversity play a part in both diseases.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.