October 23, 2013
The Truth about Lyme Disease
Killing deer can make matters worse
In a number of states, we hear a rallying cry for deer hunts to be implemented to reduce the devastating effects of Lyme disease.
Fear of this disease, and anger about our seeming inability to control it, spurs near-hysteria in some communities.
However, what is less well known is that hunting deer will not protect people from Lyme disease.
- It's a serious public health issue.
- The black-legged tick spreads the disease by ingesting and spreading a bacterium that is transmitted through blood.
- The black-legged tick itself becomes infected with Lyme disease-causing bacteria by feeding on an infected "reservoir host," an organism that carries high levels of the bacteria in its bloodstream. In most areas, this first host is the white-footed mouse.
- Deer are one of many vertebrate hosts that carry this tick. Other hosts include mice, chipmunks, raccoons, squirrels, and lizards, in addition to many popular songbirds, totaling well over 60 species.
- The black-legged tick has three active life stages (larva, nymph, and adult), which each take a single blood meal from a host. The tick seems to prefer a progressively larger host to feed upon at each life stage.
- Killing deer will not reduce the risk of Lyme disease for people.
Originally, the tick was called a "deer tick," a misnomer that has perpetuated the false belief that deer alone are responsible for Lyme disease. In truth, Lyme disease has a complex ecology in which multiple hosts and varying landscapes affect both its presence and its impact on people.
Until an effective vaccine is developed for this disease, the most important thing people can do is to practice vigilance in finding and removing ticks before infection can occur.
Killing deer can make matters worse with respect to human infection. Although adult ticks prefer a large host like deer, they will switch to alternative hosts when their preferred host species isn't available or the ticks will congregate at higher densities on any remaining deer.
Scientists warn people to be extra vigilant in areas where deer have been hunted because such areas have larger numbers of ticks "questing" for a new large host in the absence of deer—leaving people and dogs extra vulnerable. Even when the deer population is reduced by as much as 86 percent or to as low as nine deer per square mile—tick numbers do not decline enough to reduce tick reproduction or human disease.
Bottom line: You don't need to be a scientist to understand that killing one host of a multi-host disease is an exercise in futility.
If one were to really try to exterminate Lyme disease by focusing on the tick's hosts, that would mean killing most mice, chipmunks, squirrels, raccoons, skunks, rabbits, popular songbirds, and even lizards—a costly, unachievable, socially unacceptable proposition.
Another reason deer hunts don't help reduce the disease is timing. The regular hunting season occurs in November to January when many of the ticks have already dropped off the deer to lay eggs, so killing deer at this time of year has little impact on the tick's reproductive cycle.
New scientific research shows that Lyme disease incidence, and human health risks, are affected more by the abundance of the larval tick's host (white-footed mice and chipmunks) and the food resource those small hosts rely on (acorns) than by the abundance of deer.
4-Poster bait box system
One proven way to reduce tick numbers is the 4-Poster bait box system. It attracts deer to corn bait stations where a tick-killing product is applied to the deer's neck and shoulders. In essence, this device uses deer to kill ticks and has shown dramatic reductions in tick numbers in areas where it has been used. The 4-Poster bait box is commercially available in the United States, but using and maintaining it requires a special license. For more information, see http://www.liebertonline.com/toc/vbz/9/4
Homeowners can use Damminix Tick Tubes—tubes filled with permethrin-treated cotton balls which mice use for nesting material. This kills the ticks in their early larval stage when they attach to mice as their first host. Damminix tubes are an effective approach to reducing ticks and are commercially available at garden or hardware stores or the Internet.
- Check your body thoroughly for ticks immediately after removing clothing and placing everything in the washer. Do the same for your child until he is old enough to do so for himself. This is the single most important way to find ticks before they engorge themselves and are able to transmit the disease. It generally takes about 36 hours before the tick has consumed enough blood to transmit Lyme disease—thus if a tick is found within 24 hours of attaching to a person, it is unlikely it could have transmitted enough of the bacteria to cause Lyme disease.
- Steer clear of overgrown fields or wooded areas with tall grass or plants, especially in May, June, and July, when the ticks that transmit Lyme disease are most active. Stay on wide well-maintained trails instead.
- Wear light-colored clothing to make ticks easier to see. Expose as little skin as possible by tucking pant legs into socks, wearing long sleeves, and tucking in shirttails. This way you can more easily see and remove ticks before they attach themselves to your skin.
- Use insect repellent with Deet (20 to 30%) on socks and pant legs. Check with your pediatrician about the safest way to protect children from ticks; guidelines can change.
- If you find an embedded tick, remove it with fine-tipped tweezers clamped as close to the head as possible. Cleanse the area with an antiseptic.
- Modify your landscape by clearing out underbrush, rock or wood piles, stone walls, or any crevices that provide nesting or cover areas for small rodents. Keeping the grass low-cut will also reduce the number of small rodents who host the larval ticks.
An interview with Dr. Tamara Awerbuch of the Harvard School of Public Health explains in detail why killing deer won't reduce Lyme disease.
A scientific study—and entire book on Lyme disease—by leading Lyme disease expert Dr. Richard Ostfeld confirms that human risk of exposure to Lyme disease is correlated with the abundance of immature (rodent) hosts and their food resources, not deer numbers.
A study [PDF] in the Proceedings of the National Academy of Sciences found that the Lyme disease increase in the United States for the past 30 years is uncorrelated with deer abundance—and influenced more by the range-wide decline of the red fox, a key small-mammal predator.