Connecticut's War on Lyme Disease
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There’s little argument that historically, the best defense against infectious diseases has been vaccination. In 1998, the FDA approved a Lyme vaccine, LYMErix, which reduced new cases of the disease by nearly 80 percent. Yet, in 2001, manufacturer SmithKline Beecham voluntarily withdrew LYMErix from the market amidst problems with sales and reports by some who were vaccinated that as a result, they developed musculoskeletal ailments including arthritis.
A class-action suit was brought against SmithKline Beecham, claiming that the vaccine was harmful. Dr. Peter Krause, senior research scientist at Yale University School of Public Health—who participated in the development and testing of LYMErix—says, “The data supporting such a claim just isn’t there. Within any immunized population, there will always be a certain percentage of people who will develop the disease in question, which probably would have developed anyway. But because it happened around the time they got the vaccine, these people assume the vaccine was responsible.
“There’s still great interest in developing a vaccine,” he adds, “but it probably won’t appear in the near future.”
Deer are one of the most important links in the cycle that spreads Lyme disease. “Adult female ticks feed on the deer; when engorged, they drop off and lay 2,000-3,000 eggs,” says Stafford.
He points out that one can trace the history of Lyme by charting the ebb and flow of native deer populations since American Colonial times. “There was a Swedish naturalist named Pehr (Peter) Kalm who came to the U.S. around 1750, and for 20 years published a journal of his travels that noted how bad the ticks were,” he says. “A century later, the state etymologist of New York traveled the same route Kalm had and reported that he couldn’t find any ticks. What had happened in the intervening 100 years? Well, the forests were cut down, largely for agriculture, and the deer were hunted out. The best estimate we have for the number of deer we had in Connecticut in 1896 is 12 animals.”
In the 20th century, as farming moved westward and New Englanders began building and heating their homes with fuel sources other than wood, forests gradually returned, and the deer with them. “Now, a lot of people in Connecticut may see more than 12 deer in their back yards any given day,” says Stafford.
The deer population in certain communities seems overwhelming. In 1995, in Groton, it had reached 70 to 80 per square mile. “They were reporting 20 new cases of Lyme a year,” says Howard Kilpatrick, a wildlife biologist (and manager of the deer program) with Connecticut’s Department of Energy & Environmental Protection (DEEP). So, DEEP undertook a project in which the deer population in the area was reduced to 12 per square mile through a controlled hunt, and that number was maintained for five years. “Cases of Lyme dropped to two or three a year,” Kilpatrick says. “They’ve continued to allow hunting in that community.”
Such successful deer-herd culling is not an easy achievement, and it’s one that has to be approved on a town-by-town basis. “There will always be anti-hunting groups that oppose killing deer,” Kilpatrick says. Bringing the herd numbers low enough to affect the spread of Lyme (as indicated by this study) means killing up to 80 or 90 percent. A growing number of municipalities in Connecticut have been willing to make the sacrifice, particularly in Fairfield County. “The towns of Wilton, Ridgefield, Redding and Darien have all opened lands to hunting because of concerns about too many deer. Fifteen years ago, that wasn’t the case,” he says.
DEEP’s current deer study, centered on Mason’s Island, strives to reduce tick populations without killing their hosts. Deer are attracted to feed stations outfitted with paint rollers that apply a tickicide to their heads and necks. Now in its fifth year, the project has reduced tick numbers by half. A similar strategy has been tried with field mice, another critical player in the development of Lyme—they’re the primary incubators for nymph-stage ticks, and carriers of the bacterium that these ticks transfer to other hosts. Mice enter a bait-box and get painted with fipronil (the active ingredient in Frontline tick repellent). For up to a month, any tick that enters their nests is killed. “The downside,” says Stafford, “is that this approach tends to be very expensive, as mice have a very small home-range of a half-acre or so.
“We know we can kill ticks, but trying to demonstrate the impact of that on disease has been much, much tougher,” he adds. “You can reduce their numbers, but it only takes one tick to spread Lyme disease.”