A surprising connection between invasive plants and Lyme disease

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Researchers from the Connecticut Agricultural Experiment Station returned from studying invasive woodland plant species one day to find themselves mysteriously crawling with ticks.

"I've been working in these forests for 30 years, and I'd never been covered with ticks like that before," recalls Jeffrey Ward, chief scientist with the station's forestry and horticulture division.

It was a puzzle that triggered new research and a surprising link between an invasive plant, our rising deer population, and one possible explanation for why Lyme disease has become such a health threat.

The woods through which Ward and his colleagues walked that day were filled with dense patches of Japanese barberry.

Introduced into New England in 1875, once Japanese barberry spread, having no natural predators or pests in North America, this ornamental import went wild. It can now be found in patches hundreds of acres across in some Connecticut towns.

Turns out that Japanese barberry is poisonous to deer. So deer browse on other woodland plants, which would otherwise compete with barberrry for space, sunlight and nutrients. Less competition gives this insidious invader more opportunity to spread, which it does with amazing speed in favorable locations.

"It spreads across the landscape like a fungus," Ward warns.

Dense patches of Japanese barberry leaves are a perfect place for ticks to cling.

In areas where there are lots of deer there are more ticks carrying Lyme disease.

An experiment carried out by Ward and his colleague Scott Williams, an assistant scientist at the station, found that woodland areas uncontaminated with barberry had about 10 Lyme-disease-ticks per acre. In sections with dense Japanese barberry, the number of disease-carrying ticks was as high as 126 per acre. When they killed off all the alien barberry they could find in a specific portion of forest, the Lyme tick count rapidly dropped to about 41 per acre.

And guess where you can find some of the biggest, densest concentrations of Japanese barberry in this state?

That's right: Lyme, Connecticut, the place for which the disease is named. "In Lyme, there are huge patches," Ward says.

It was in Lyme, in 1975, that doctors decided to classify the 50 cases of pediatric arthritis that had turned up as a new illness. (Later research traced indications of the disease as far back as 1883 or much earlier.)

The trip into the woods that started this line of research occurred back in 2007, according to Ward. Scientists at the station and at the University of Connecticut have been studying the connection ever since.

One confirmation of those studies is that, in states with high concentrations of Japanese barberry invasions, you also have high incidences of Lyme disease ticks.

This stuff isn't easy to kill. Recommended treatments includes burning it out with controlled fires, using propane torches, brush saws, or (if it's taller than 3 feet high) mechanical "drum choppers," expensive machines that sort of resemble a combination snow blower and roto-tiller.

Ward is still dazzled by the unanticipated connection between an alien plant and the spread of an insect-born disease.

Ward says the apparent link between Lyme disease and this plant was one orf the most interesting findings they've had.



Photo Gallery:  The Department of Forestry & Horticulture searches for Lyme Disease-causing ticks

PDF:  The Department of Forestry & Horticulture's January 2012 brochure of Lyme Disease information

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