Bardian SPRING 2011

felicia keesing
biodiversity’s impact
on infectious diseases
Associate Professor of Biology Felicia Keesing was lead author on an important article in Nature, “Impacts
of biodiversity on the emergence and transmission of infectious diseases” (December 2, 2010), the salient
points of which she reproduces here. The article garnered national and international attention, including
notice in the New York Times under the headline, “As Biodiversity Declines, Disease Flourishes.” Keesing has
received grants from the National Geographic Society, National Science Foundation, and National Institutes
of Health. Her awards include the Patricia Roberts Harris Fellowship, Anna M. Jackson Award, and prestigious
Presidential Early Career Award for Scientists and Engineers, which represents the priority the U.S.
government places on nurturing the professional development of outstanding scientists and engineers.
In March, a team on which she is an investigator received a $300,000 grant from the U.S. Environmental
Protection Agency to assess environmental risk for Lyme disease in Dutchess County, New York.
The Hall of Biodiversity in the
American Museum of Natural
History
©George Steinmetz/Corbis
Public health initiatives increasingly emphasize the importance of preventing the transmission of infectious
diseases, rather than just treating infections after they occur. A number of ambitious public
health efforts—including vaccination campaigns, the eradication of pathogens like polio, and focused
care for genetically susceptible individuals—are all examples of this new preemptive medicine. But
the full development of preemptive medicine must incorporate another type of strategy as well. Recent
research has demonstrated that biological diversity (biodiversity) in ecological communities—whether
in agricultural fields, coral reefs, barns, or the insides of human bodies—can affect the transmission
of infectious diseases. In a recent paper in Nature, my colleagues and I described how understanding
the ecology of infectious diseases in nature can help predict, prevent, and mitigate the spread of infections
in humans, wildlife, domesticated animals, and plants.
Biodiversity encompasses the diversity of genes, species, and ecosystems. Increases in human
populations have resulted in an unprecedented and precipitous loss of biodiversitythroughout the world.
Current extinction rates are estimated to be at least 100 to 1,000 times background extinction rates and
extinction rates over the next 50 years are estimated to be 10 to 100 times present extinction rates. Every
major group of organisms faces extinction threats: 12 percent of bird species, 23 percent of mammals,
32 percent of amphibians, and 33 percent of corals. Furthermore, the global abundances of birds, mammals,
amphibians, reptiles, and fish have declined by almost 30 percent since 1970. Collectively, these
declines and extinctions are caused by changing the earth’s ecosystems to meet the growing demands of
human populations for food, fresh water, fiber, timber, and fuel; and by climate change.
How might the decline of biodiversity affect infectious disease? Infectious diseases by definition
involve interactions between at least two species—the pathogen and its host. For example, humans
with influenza have been infected with a virus transmitted to them by another human. Often many
more species are involved, including other species of hosts. Tuberculosis, for example, is caused by
the bacterium Mycobacterium tuberculosis, which can be transmitted back and forth between humans,
cattle, and other animal host species. Some diseases also have vectors—meaning they transmit the
biodiversity 3