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Luring mice to combat Lyme disease
Updated 11:11 pm, Monday, April 8, 2013
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Assistant professor Neeta Connally holds a rodent targeted tick control device in her lab at Western Connecticut State University in Danbury, Conn. Monday, April 8, 2013. Photo: Michael Duffy / The News-Times
The fight against Lyme disease involves spraying yards, killing deer and checking daily for ticks to make sure no blood-seeking travelers are residing on our bodies.
But what about the great, scurrying reservoir of Lyme bacteria -- white-footed mice?
A scientific study is underway to learn whether treating backyard mice with an insecticide, delivered in a black plastic bait box, can reduce the number of human cases of Lyme disease.
"We know it can reduce the number of ticks and the number of mice carrying Lyme disease," said Neeta Connally, assistant professor of biological and environmental science at Western Connecticut State University in Danbury. "The purpose of the study is to see if it can reduce the number of Lyme disease cases in humans."
The work is being conducted by the Centers of Disease Control and Prevention, the Connecticut Emerging Diseases Program, which is run by the Yale University School of Public Health and the state Department of Public Health, and Western.
In the second year of a three-year study, the CDC is seeking 500 homeowners in 15 towns in Fairfield and Litchfield counties including Bethel, Bridgewater, Brookfield, Easton, Monroe, New Fairfield, New Milford, Newtown, Ridgefield, Roxbury, Trumbull, Weston, Westport, Wilton and Woodbury.
"I don't think we'll have any trouble," Connally said about finding willing participants.
Treating mice to stop a human disease is an indication of how complicated Lyme disease can be.
The black-legged ticks that carry and spread the bacteria that causes the disease, Borrelia burgdorferi, need three meals of blood during their lives. Their first comes in the larval stage. If they feed on white-footed mice, or other small rodents at this stage, their meal may include the Lyme bacteria.
Their next meal comes in the following spring or summer when ticks are nymphal stage -- tiny, poppy-seed size insects. If they latch onto a human being for this feeding, they can transmit the bacteria.
Most humans get Lyme disease in late spring and early summer from nymphal ticks.
Their final blood meal comes in the fall. By then, the ticks are adults. While they can still spread Lyme disease at this stage, they're much easier to see and to remove.
The bait boxes are intended to break the chain of transmission at the mouse level.
They look like little mazes. The mice walk into them, lured by the food in the box. To get to the food, the mice have to walk though soft fabric wicks treated with Fipronil, the insecticide commonly used on pets to kills ticks. The wicks brush the mice and kill the ticks on them.
Connally said the federal Environmental Protection Agency has approved the use of Fipronil.
"It's already on the market," she said.
Mouse bait boxes have been commercially available for years. Kirby Stafford, an entomologist at the Connecticut Agricultural Experiment Station in New Haven, used them in studies on tick control on Mason's Island in Stonington and found they caused a marked reduction in overall tick numbers and the number of ticks infected with the Lyme bacteria.
"You are treating the transmission system," he said.
The ongoing study, however, looks at the next step, whether the bait boxes can reduce the number of human cases of Lyme disease.
To do that, the study will be a double-blind study, the method considered the gold standard of scientific research.
Half of the families that enroll in the study will receive bait boxes with Fipronil. The other half will get boxes with a placebo.
None of the people involved with the project, the CDC, Connally and her students at Western, the state Department of Public Health or the Yale School of Public Health, will know which families get the bait boxes with the insecticide and which get the placebo, until the study ends and the researchers start analyzing the data.
Dr. Randall Nelson, an entomologist and epidemiologist with the state Health Department, said other studies are underway to find the best method of controlling the spread of Lyme disease.
The CDC is funding a $900,000 study in Redding, to be carried out by the agricultural experiment station, that will look at the best combinations of methods to stop the disease.
Nelson said the bait box study is focused on scurriers.
"The concept of using bait boxes is not new, but the specific focus is," he said. "We want to look at mice and the part they play in the environment."
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