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 being published this week in Proceedings of the NationalAcademy of Sciences.
Kathleen LoGiudice, an assistant professor
of biology at Union
College,
and colleagues investigated the relationship between biodiversity and Lyme
disease, an illness transmitted between ticks and many vertebrates, including
humans.
The researchers captured 13 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 40 to 90 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 said. For example, development in rural townships –
even those with minimum lot sizes as large as five acres – can cause a forest
fragmentation that results in less biodiversity and a
higher density of mice. The challenge to planners, she said, is to maintain
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, transmitted to humans by a
bacteria from the bite of infected black-legged ticks, each year affects about
16,000 people, mostly in the northeast U.S.,
according to the Centers for Disease Control web site: http://www.cdc.gov/ncidod/dvbid/lyme/diagnosis.htm
LoGiudice was lead author of the PNAS paper
titled, “The ecology of infectious disease: Effects of host diversity and
community composition on Lyme disease risk.” The paper is to appear on-line
this week at http://www.pnas.org and
forthcoming in the paper edition of the journal. (The paper is to appear under the heading, “PNAS Early Edition.”)
LoGiudice's
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.
LoGiudice and her colleagues captured
species ranging from mice to deer and then “took the ecosystem apart to determine
how much each species was contributing to the infection prevalence in the
ticks,” she said. Using these data, they calculated that the more host species
there were, the lower the disease risk would be. These results were strongly
supported by seven years of data collected at the same study area. Thus, in
areas with more biodiversity, there appears to be a “buffering of human risk of
exposure” to Lyme disease.
For more information,
contact Kathleen LoGiudice, department of biological sciences, Union
College;
518-388-6409, fax 518-388-6429, or e-mail .