The goal, federal and state health officials say, is to find a new way to prevent the widespread illness, which is spread by tick bites and can cause fever, headaches and fatigue — and, if untreated, may even affect joints, nerves and the heart.
"The question is, does it actually prevent a common, sometimes severe disease — and second, what's the lowest dose you can do?" said Dr. Clifford S. Mitchell, assistant director for environmental health and food protection in the state Department of Health and Mental Hygiene.
Environmental activists, though, contend that the study itself is putting the families at risk. Adults and children alike are being exposed to a pesticide that is classified by the Environmental Protection Agency as a possible carcinogen, critics say, and that is being studied by the EPA for possible harm to reproductive and immune systems, among other things.
"It's improper to be conducting a human experiment like this," said Jay Feldman, executive director of Beyond Pesticides, a national group based in Washington. He and other activists contend federal and state health officials have not adequately informed volunteers about all the potential health risks.
The study, now in its second year, was underwritten by the U.S. Centers for Disease Control and Prevention. The pesticide also is being tested on yards in Connecticut and New York. Last year, 440 other Maryland families participated.
Lyme disease, so named because it was first reported in Lyme, Conn., is a bacterial illness transmitted when people are bitten by blacklegged ticks, more commonly known as deer ticks. It has become a major health concern in the Northeast and Mid-Atlantic, where a burgeoning population of deer have helped spread the disease beyond forests into suburbia.
There were 30,000 cases reported in 2010, according to the CDC, with the vast majority in those two regions. Maryland had 1,600 cases that year, well below the peak of more than 2,500 cases reported in 2007. But health officials believe that doctors often miss or don't report cases, and the actual number could be 10 times higher.
Many people living in the most affected states already have resorted to spraying their yards with pesticides to get rid of ticks, said Katherine Feldman, the state public health veterinarian. A survey in Connecticut found that 29 percent of homeowners contacted already pay a pest-control company to treat their properties, she said.
Health officials said it appears that a significant number of people do get bitten by infected ticks around their homes, not just when they go hiking through tall grass or a forest.
There's also evidence, they say, that the number of ticks in a yard can be reduced significantly by applying bifenthrin, a synthetic chemical similar to the natural insecticides produced by flowers like chrysanthemums.
"We know that pesticides are extraordinarily effective against ticks," Mitchell said. "We don't know if they result in a decrease in human disease."
Feldman, the state health veterinarian, said volunteers were recruited for the study by mailing fliers to residents in ZIP codes that have had a high incidence of Lyme disease.
The fliers sought single-family households with at least two people who were willing to have a "single, no-cost, commonly used pesticide application" to their yard and answer "short surveys" about ticks and their yards. For their trouble last year, they were offered $40 gift cards to a local grocery store, paid for by the CDC, according to the state veterinarian. The reward for this year's recruits has been scaled back to $25 gift cards.
Veronika Carella, who lives in western Howard County, was among those invited to participate last year. She said she was appalled because her two children, now in college, have been registered for years on the state's list of chemically sensitive people. Though their 3.5-acre yard has woods and five resident deer — and her elderly mother contracted Lyme disease, most likely elsewhere — Carella said she believes the disease can be prevented without resorting to pesticide use.
Carella and others contend that prospective volunteers weren't informed clearly enough about the potential long-term health risks from being exposed to the pesticide.
"When you get a prescription, you're told all the things that can happen to you, including perhaps dying," said Ruth Berlin, executive director of the Maryland Pesticide Network, a coalition that seeks to limit pesticide use. She said the basic message given to prospective volunteers was that the pesticide is safe, which she disputes.
An EPA analysis of bifenthrin notes that there were nearly 1,300 incidents involving the pesticide from 2002 to 2009, and that while most were of "low severity," it appeared that even low amounts of the chemical can cause skin and respiratory irritation and dizziness.