We read with interest the online comments in response to the article headlined “Vineyard Legislators Back Chronic Lyme Treatment Bill.” People clearly recognize the severity of the problems caused by Lyme disease and other tick-borne illnesses. However, there appears to be considerable confusion about ticks, the role of their different host animals and what can be reasonably be done to reduce the high incidence of Lyme disease and other tick-borne illnesses on Martha’s Vineyard.
People can do many things to protect themselves from tick-borne illness, including wearing protective clothing, using tick repellents and conducting frequent tick checks. There are also many things people can do to reduce the number of deer ticks in their yards, including removing dead leaves, trimming branches to increase sunlight, spraying the edges of the yard to kill ticks, and creating a three-foot-wide gravel or mulch buffer around the edge of their yard. Detailed information about these and other techniques can be found on the boards of health website at mvboh.org.
But while making individual yards safer is important, it represents a patchwork solution at best, given the Island’s large deer population. Aerial surveys and estimates from the Massachusetts Division of Fisheries and Wildlife indicate that Martha’s Vineyard may have as many as 5,000 deer, or 50 deer per square mile.
Significantly reducing the number of deer is the only documented economically feasible way to reduce the incidence of Lyme disease over a large area such as the Vineyard. Studies published in peer reviewed scientific journals demonstrate that reducing the number of deer in an area results in a decrease in the number of ticks and the number of people in that area getting Lyme disease.
A recent study done in a Connecticut community following a hunt to reduce the herd found that reducing deer density to 5.1 deer per square kilometer resulted in a 76 per cent reduction in tick abundance and 80 per cent reduction in resident-reported cases of Lyme disease. Closer to home, blood samples from seasonal residents of Naushon showed a 40 per cent decrease in Lyme disease antibodies after coyotes reduced the island deer population by 85 per cent.
Because deer ticks get the Lyme disease bacteria when feeding on white-footed mice, people have suggested we should focus on reducing mice populations instead of deer. In theory this could work. In reality, there are so many mice and they reproduce so quickly that it would be almost impossible to reduce the mouse population enough to have an effect on the number of people getting Lyme disease.
Deer play a different, crucial role in the deer tick life cycle. In the fall, female deer ticks feed on deer and other larger mammals, including humans. On Martha’s Vineyard, the only significant natural host for adult deer ticks is deer; there are no foxes or coyotes and deer ticks do not feed well on raccoons, skunks or rabbits. Adult males do not feed, but are on the deer looking to mate with the females. Once the female has fed and mated, she drops off and lays as many as 2,000 eggs. If the adult female doesn’t find a deer or other large mammal to feed on, she will eventually die without laying eggs.
In short, although deer ticks do not get the Lyme disease pathogen from deer, deer are responsible for deer tick reproduction. Reducing the density of deer will reduce the number of female deer ticks that feed, mate and lay eggs, causing the tick population to decline over time.
Another important consideration is the increase in lone star ticks on Martha’s Vineyard and the Elizabeth Islands, since lone star ticks also depend on deer for their life cycle. At the moment, with the exception of a few hot spots, lone star ticks are present in low numbers on the Vineyard. However, we expect their numbers to increase, perhaps dramatically, over the next few years. A significant reduction in the number of deer represents our best chance of preventing an explosion in the number of lone star ticks and the problems this has caused on other Islands, including Cuttyhunk, Long Island, N,.Y., and Prudence Island in Rhode Island.
We recognize that any serious effort to reduce Lyme disease and other tick-borne illnesses will need to employ multiple methods at multiple points in the life cycle of a tick. An excellent summary of these alternatives is available at the following link: snyderfarm.rutgers.edu/pdfs/Managing-Urban-Deer-CT.pdf.
Nonetheless, along with public education, we believe that a reduction in the number of deer is the most feasible and cost effective step we can take to reduce the incidence of tick borne illnesses on the Vineyard over the long term. Starting to manage deer more effectively now will make the Island safer for our children’s children.