The researchers followed up on an earlier study that showed that black-legged
ticks, which carry the disease, tend to hide under leaves, something their
northern counterparts don't do. They said this keeps them out of the way of most people.
The Rhode Island and USGS researchers go a step further, contending in their study published in the Jan. 11 issue of PLOS ONE
that the ticks hide under the leaves to retain moisture and stay alive. The northern insects don't have this issue. In fact, a lack of moisture kills off many ticks that could otherwise bite humans, the researchers argue.
"There has been a lot of research aimed at finding out what makes
black-legged ticks more efficient hosts for Lyme disease in the North than in
the South,” URI Professor Roger LeBrun said. “People have looked at everything
from the effects of temperature on tick life cycles to the types of animals the
ticks feed on. Probably all of these play a role. But our results suggest that
evolutionary pressure to conserve moisture by staying under the leaf litter
surface is a critical factor.”
Approximately 300,000 Americans get sick from Lyme disease each year, with a
disproportionate amount in the northern part of the country. For example, there
were 11 confirmed cases in Alabama in 2015, but Vermont, which has 700,000
fewer residents, had 491.
“In the North, when you walk through the woods you’re walking right through
tick habitat,” Howard Ginsberg, a USGS research
ecologist who leads the USGS Patuxent Wildlife Research
Center’s field station at URI, said. “In the South, you’re walking on top of the habitat.
We think that is a crucial difference.”
Climate called culprit in Lyme disease's prevalence in US North
Lyme disease is less common in the southern United States
because the ticks that transmit it tend to die from dehydration in areas with
high heat and lower humidity, researchers from the University of Rhode Island
and the Geological Survey (USGS) said recently.