Science Wednesday: Biodiversity and Lyme disease – In the Field

Each week we write about the science behind environmental protection. Previous Science Wednesdays.

Recognizing that there is a need for more scientific studies characterizing the mechanistic pathways linking social stressors (deforestation, habitat fragmentation, climate change), biodiversity, and human disease transmission, EPA developed a Biodiversity and Human Health research initiative to develop and sponsor long-term and pilot research projects.

The Biodiversity and Human Health research projects are the first of their kind at EPA, in subject matter and approach. The approach is interdisciplinary, involving ecologists, public health specialists, social scientists, and earth scientists. One unique part of the studies is that decision-makers are included in the research process, so that new findings of scientific knowledge can quickly be put into practice.

Starting tomorrow, I’ll be making a field site visit to one EPA-sponsored research project.

Rick Ostfeld, of the Cary Institute of Ecosystem Studies is leading a project entitled “Mechanisms Linking Host Biodiversity to Lyme Disease Risk: An Experimental Approach” to investigate how differences in animal community composition affect Lyme disease transmission in Duchess County, NY.

People get Lyme disease by being bitten by a tick infected with the spirochete bacterium, Borrelia burgdorferi. Ticks acquire the Lyme disease bacterium by feeding on small mammals such as white-footed mice (Peromyscus leucopus) and chipmunks that are already infected.

Not all mammals are equally efficient or competent at transmitting the bacteria to ticks when fed upon. In fact, white-footed mice appear to be the most competent animal host reservoir of Lyme disease in the northeastern U.S. So, the more white-footed mice that are in the forest, the greater chance more ticks will be infected, and the greater chance you have of getting bitten by an infected tick.

In a previous blog, I mentioned that forest destruction and fragmentation in the U.S. have been shown to reduce mammalian species diversity, and to increase populations of the white-footed mouse. Rick and his team will be manipulating the composition of small mammals across a variety of forest plot types to see how high and low levels of mammal diversity may affect Lyme disease infection rates among feeding ticks.

In a seminal paper, Rick and his colleagues proposed the “dilution hypothesis” to help explain how high biodiversity can decrease the risk of Lyme disease transmission. It predicts that infection rates for a specific pathogen (e.g. Lyme disease bacterium) will be lower in highly diverse host communities. Why? The “incompetent” reservoir hosts dilute rates of transmission between vectors (ticks) and competent hosts (white-footed mice). With EPA support, Rick’s team will be collecting and analyzing field data to help characterize the scientific mechanisms that can explain how different levels of biodiversity affect Lyme disease risk.

image of authorFor more information on EPA’s Biodiversity and Human Health activities, see:
http://www.epa.gov/ncer/biodiversity

About the author: Montira Pongsiri, PhD, MPH, is an Environmental Health Scientist in EPA’s Office of the Science Advisor.

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Follow the action from our field trip. We’ll posting updates from EPA’s new research Twitter account: @useparesearch.