Excluding deer could be a counterproductive strategy for controlling tick-borne infections, because the absence of deer from small areas may lead to an increase in ticks, rapidly turning the area into a potential disease hotspot, according to a team of U.S. and Italian researchers.
"Deer are referred to as dilution hosts or dead-end hosts," says Sarah Perkins, a postdoctoral researcher at Penn State's Center for Infectious Disease Dynamics. "They get bitten by ticks but never get infected with tick-borne pathogens, such as the bacteria causing Lyme disease."
However, deer are critical to adult female ticks in the last stages of their three-part lifecycle. Ticks use them for a final blood meal before dropping off to produce thousands of eggs, Perkins explains. Currently, health officials believe that removing deer from the equation could disrupt the tick lifecycle and leave fewer ticks to feed on rodents, which, unlike deer, can transfer a range of tick-borne pathogens. Ultimately the tick-borne disease will fade out.
However, previous field studies show that removing deer sometimes leads to higher tick densities and sometimes lower, and the outcome seems dependent on the size of area from which deer are excluded.
"Very few studies have looked at how removing the deer affects the intensity of tick bites on rodents, and how it relates to the size of the area from where the deer are excluded," explains Perkins, whose findings are published in the current issue of the journal Ecology.
Researchers first collected data from published information on tick densities in deer excluded areas ranging in size from roughly 2.5 acres to 18 acres. Next, over a six-month period, they captured rodents from a 2.5-acre deer excluded area in the Italian Alps in a known hotspot for tick-borne encephalitis -- a disease passed to humans through the bite of an infected tick.
"From previous studies we found that tick densities decreased in (geograp
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Contact: Amitabh Avasthi
axa47@psu.edu
814-865-9481
Penn State
30-Aug-2006