Scientists have tried all sorts of strategies for stopping the blacklegged tick, the carrier of Lyme disease, from biting us.
Lyme disease is a bacterial infection that affects an estimated 300,000 people in the United States each year, primarily in the Northeast and upper Midwest.
Stopping the tick bite in the first place is key to limiting Lyme disease.
"I spend a lot of time counseling people on tick bite avoidance," says Dr. Anne Norris, an infectious disease specialist at the University of Pennsylvania Perelman School of Medicine. "Right now prevention techniques are all we have. We don't have an effective vaccine."
But researchers have tested more strategies for keeping ticks away from us. Many more.
In a review paper published Wednesday in the Journal of Medical Entomology, scientists Lars Eisen and Marc Dolan of the Centers for Disease Control and Prevention analyze the past 30 years of evidence for techniques to prevent blacklegged tick bites. They focus on studies that looked at preventing nymph bites (as opposed to bites from ticks in the larva or adult stages) because nymphs, which are active from May through July, are the most likely to spread Lyme.
Many of the strategies are designed to limit exposure by reducing the number of ticks in backyards, or at least the part of backyards more likely to be used by humans. They include:
Create a barrier. Ticks love to hang out in the area where a lawn meets the woods. If you have a wooded edge on your property, you may want to consider removing this habitat by creating an artificial border about a yard wide between the woods and lawn. Scientists have tried making borders out of everything from crushed stone and wood chips to sand and sawdust. More research is needed — none of these materials stopped ticks in their tracks entirely — but sawdust from the Alaska yellow cedar seemed to be the most promising option.
Spray pyrethrin insecticides. Studies have shown that treating wooded areas with sprays made from pyrethrins, compounds found in chrysanthemum plants, can dramatically reduce the number of blacklegged ticks. But the effect wears off within a few weeks, so homeowners who want to try this strategy would have to reapply regularly. And the spray can kill beneficial insects like honeybees, too. Pyrethrins typically don't harm people or other mammals, but they can cause some irritation if touched or inhaled.
Put a robot on the job. OK, you can't actually hire a robot to remove ticks from your yard this summer, but you may be able to someday. Scientists have designed a robot to control tick populations. Dubbed the TickBot, this four-wheeled robot collects and kills ticks by dragging a permethrin-treated cloth. Early testing looks promising, but scientists haven't yet tested the robot on the blacklegged tick or looked at its long-lasting effects on tick abundance.
Help the mice help you. Rodents are one of the main carriers of Borrelia burgdorferi, the bacterium that causes Lyme disease. Ticks often pass the bacterium on to us after picking it up from rodent hosts, especially the white-footed mouse. If we could find a way to prevent mice from picking up ticks, we might be able to limit our own exposure to the disease. Enter the Damminix Tick Tubes. These are cardboard tubes filled with cotton balls treated with permethrin. Homeowners place the tubes in their yards and then mice use the cotton balls to build nests. The goal is for the permethrin to kill the ticks on the mice.
In some residential settings, tick tubes have proved to be highly effective at freeing white-footed mice from tick infestations. But in many cases, overall tick abundance in a treated area has remained high, possibly because the ticks survived on other vectors such as voles, shrews and squirrels.
Fence out the deer. Blacklegged ticks can't contract the bacterium that causes Lyme disease from deer, but the adult ticks do feed and reproduce on them. So reduce the number of deer in an area and you will likely reduce the number of ticks. Homeowners can consider using deer fencing to eliminate deer from their yards. Studies have shown that deer fencing can significantly reduce tick numbers, but this tactic typically only works for properties larger than 7 acres.
None of these methods is a "silver bullet," says review author Eisen. "It's looking more and more likely that there is no single method that will be sufficient to substantially reduce Lyme disease in the absence of a human vaccine."
Kirby Stafford, chief entomologist for the Connecticut Agricultural Experiment Station, agrees with Eisen's conclusion. "No one single tool other than waving a magic wand and making all the deer disappear will bring [tick] numbers down to a point where people aren't being infected," he says.
Eisen and Stafford both say that scientists now need to focus on testing combinations of tick-prevention techniques to find out which integrated approaches work best.