Healthy, Diverse Bird Population Is Good For Human Health, Too

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William & May biologist John Swaddle examines a young bluebird. Photo courtesy of the College of William and Mary

WILLIAMSBURG, VA (06/25/2008)(readMedia)-- Researchers from the College of William and Mary have discovered that what's good for an area's bird population also is good for people living nearby-especially during an outbreak of West Nile virus, a disease which can be passed from wildlife to humans.

A study by biologist John Swaddle and an undergraduate student, Stavros Calos '08, found that areas which have a more diverse bird population show much lower incidences of West Nile virus infection in the human population. West Nile develops rapidly in bird populations, then can be passed to humans or other animals through a vector mechanism, often a mosquito.

The findings, published in the online peer-reviewed journal PLoS One, constitute the largest-scale application to date of the "dilution effect." Swaddle explained that the dilution effect is a pattern whereby increased biodiversity in wildlife results in lower risks of humans contracting "zoonoses," animal diseases which can infect humans. The dilution effect was first reported in Lyme disease, where ticks spread the disease from small mammals to humans. The Swaddle and Calos study is the first to demonstrate the dilution effect in a disease that has bird hosts. Other zoonoses of concern, such as avian flu and bubonic plague, Swaddle said, may fit the dilution effect as well.

"We don't yet know the precise mechanism that drives this pattern, but it's likely to be due to diverse areas having relatively few of the bird species that are particularly competent hosts and reservoirs for the virus," Swaddle said.

Host competence, he explains, refers to a set of qualities that make a particular species of bird best able to contract the disease and pass it on through a vector. The highest levels of host competence are found in crows, jays, thrushes and sparrows-the very birds that tend to thrive when avian biodiversity is reduced.

Swaddle pointed out some implications of his research. Very small changes in land management, he said, could attract more bird species, with the increase in biodiversity paying off in the form of lower human infection rates during outbreaks of West Nile or other zoonoses in the bird population.

Swaddle is an associate professor of biology and director of the environmental science and policy program at William and Mary. He began the work in conjunction with the interdisciplinary biomath program, which uses mathematical tools to explain biological phemonena. He completed the work during the past year as a sabbatical fellow at the National Center for Ecological Analysis and Synthesis in Santa Barbara, California.

"Biodiversity is giving us a public health service that people have rarely considered and the value of this service should be considered when developing land and managing bird populations in the future," Swaddle said.

The study is available at http://www.plosone.org/doi/pone.0002488.

Contact: Professor John Swaddle, William and Mary Department of Biology 757-221-2231

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