The loss of biodiversity that can result from the development of rural countryside appears to be putting humans at increased risk of contracting Lyme disease, according to a paper published this winter in
Proceedings of the National Academy of Sciences.
Kathleen LoGiudice, an assistant professor of biology at the College, and colleagues investigated the relationship between biodiversity and Lyme disease, an illness transmitted between ticks and many vertebrates, including humans.
The researchers captured thirteen species of birds and mammals that host ticks, and tested ticks feeding on the animals for Lyme disease. They then calculated the contribution of each species to the total proportion of infected ticks. The results show that as biodiversity declines, Lyme disease risk increases. This is because in areas with high biodiversity, more ticks feed on species that do not effectively carry or transmit Lyme disease.
However, in degraded areas of low species diversity, the ticks feed mostly on white-footed mice, which transmit Lyme disease to forty to ninety percent of the ticks that feed on them. The authors suggest that because mice are one of the last species to disappear as habitat is degraded, loss of biodiversity increases the chance that ticks will feed on mice and pass on Lyme disease to humans.
The findings could have implications for land use
policy, LoGiudice says-although she cautions that her research is preliminary and the results need to be repeated several times before they could be used as a guide for policy.
But if the same results were found in further research, one conclusion might be that development in rural townships-even those with minimum lot sizes as large as five acres-can cause forest fragmentation that results in less biodiversity and a higher density of mice. The challenge to planners, then, would be to maintain enough continuous forest that can serve as habitat for “dilution hosts” such as squirrels, shrews, opossums, and raccoons that do not as readily transmit the disease.
Lyme disease is spread by ticks that live in wooded and grassy areas. The disease, which is caused by a bacteria and transmitted to humans from the bite of infected black-legged ticks, affects about 17,000 people each year, mostly in the northeast U.S., according to the Centers for Disease Control. New York State reported 5,036 cases outside of New York City in 2002, a twenty-six percent increase over 2001. The disease causes fatigue, fevers, and joint pains that can persist for weeks. Some patients develop severe arthritis. If not treated with antibiotics, Lyme disease can severely damage the heart and nervous systems.
LoGiudice was the lead author of the paper titled, “The ecology of infectious disease: Effects of host diversity and community composition on Lyme disease risk.” Her colleagues were Richard Ostfeld of the Institute of Ecosystem Studies in Millbrook, N.Y.; Kenneth Schmidt of Texas Tech University; and Felicia Keesing of Bard College. The research was done at the Institute of Ecosystem Studies.
The researchers have received a $1.6 million grant from the National Institutes of Health to expand their work over four years in six states-New York, Massachusetts, Connecticut, New Jersey, Pennsylvania, and Maryland.