Unwelcome amenity may lurk in those woodsy new exurbs:

more Lyme disease

by Ashley Manton

Owners of homes built in isolated areas risk more tick bites and subsequent Lyme disease infections, researchers have found.

Although most cases of Lyme disease are reported in Northeastern states, incidence rates are increasing across the country. The disease is spreading northward into Maine and as far south as North Carolina. In 2005, 23,205 cases were reported nationwide, roughly 47 times the number of cases reported when nationwide data was first collected in 1982. Lyme disease was first identified in 1975.

According to Dr. Laura Jackson, landscape ecologist at the Environmental Protection Agency and lead researcher on a recent study investigating the relationship between landscape design and incidence rates of Lyme disease, the locations of development are significantly related to the increasing number of Lyme disease cases.

“When people go out to farmland and buy it up, the densities can be one unit per five or 10 acres, and that’s such low density,” said Jackson, whose study was published in the International Journal of Epidemiology. “You have people moving out into the exurban environment, and then you have a lot of reforestation going on, so the two of those forces combine to form these patchy landscapes, which are ideal for Lyme disease.”

These patches, created when development cuts the amount of continuous natural forest into smaller, divided pieces, bring people into closer casual contact with ticks. Evidence suggests that in these conditions, the relative densities of the white-footed mouse, the most effective reservoir for carrying the bacterium, are increasing.

Jackson’s study investigated the incidence rate of Lyme disease across 12 Maryland counties and, through the Maryland Department of Health records, linked individual cases to their residential locations. This provided a closer look at whether infection increases with landscape fragmentation.

As forestland is divided into patches for development, a number of species that do not carry Lyme disease cannot survive, so ticks can't feed of them. Predators of the white-footed mouse also disappear. So the mice and the infectious ticks are left, to increase together, Jackson figures.

The numerous experiments to check for links between human infection rates and forest fragmentation have debatable aspects, especially concerning the locations of these tests.

Harvard faculty member Dr. John Brownstein conducted a 2005 study in Lyme, Connecticut, and 12 surrounding towns, a highly urbanized area, and found different results. Brownstein found that although there are higher densities of infected ticks in areas that have been fragmented, living in highly urbanized areas decreases human risk of infection.

“This particular infection is really tied to the environment. If you keep fragmenting an area, you might get increasing ticks and increasing infection, but you’re putting people farther and farther away from the ticks,” Brownstein said. “It doesn’t matter if a tick is infected in the middle of nowhere and there’s no human to be infected. That’s no risk.”

According to Brownstein, because most people are infected near their homes, “if they’re not near the tick they won’t get infected.”

An approach that might help decrease the prevalence of the disease, Jackson said, is concentrating more on what will benefit the health of society and less on the desires of individuals. By clustering homes together and concentrating people in smaller areas, as opposed to sporadically spreading homes throughout forests on sizeable pieces of land, larger chunks of forests will remain in their unaltered, original states with more native biodiversity intact.

“Some diseases, diseases that are intimately entwined with the environment, are going to involve more landscape planning and design,” she said. “I wish people could become more enamored with town life again. When you talk about more high density, people say, ‘I don’t want it to be like New York City.’ But that’s an extreme example.”

She offered simpler solutions than complete urbanization, such as constructing more two- and three-story commercial buildings and reducing vast parking lots. These techniques would bring homes and businesses closer together. Although a Lyme disease vaccine was developed, it was not widely purchased, and its effectiveness was low.

One solution that has been “sort of effective,” according to Jackson, are mouse feeding stations. When white-footed mice enter these traps, the walls coat the mice’s fur with acaricide, a tick poison, killing the ticks that have attached themselves to the mice.

Dr. Richard Ostfeld, a tick expert at the Institute of Ecosystem Studies in Millbrook, New York, conducted a 13-year study investigating the relationship between ticks and their hosts, such as mice, chipmunks and shrews. He recently expanded the study from Dutchess County, New York into areas of Connecticut and New Jersey. These three states, along with Pennsylvania, have the four highest total cases of reported human infection.

“It’s phenomenal how many cases there are and there is very considerable underreporting,” Ostfeld said. “The threat of Lyme disease has such an effect on people’s attitudes toward nature: Whether they’re willing to walk off in the woods, let their dogs go off leashes and kids go off of trails and even if they are willing to garden.”

The Lyme Disease Foundation estimates that only one in every ten cases of Lyme disease, the most common vector-borne illness in the United States, is actually reported to the Center of Disease Control and Prevention.

As the numbers of Lyme disease cases are continually increasing, Jackson claims it is the everyday routines of people living in low-density areas that are most threatening for human infection.

“It has been found that the people who work out in forest environments like foresters, landscapers and people who go camping actually have lower rates of Lyme disease infection than people who contract it around their homes,” Jackson said. “These people are mindful of the dangers and take precautionary measures, but people who are living in sprawl-type areas are going to take out the trash or pull tomatoes from the garden and they’re not suiting up to go out. That’s why most of the exposure we see is around the home.”

Regardless of location and incidence rates, if not treated correctly, Lyme disease can linger for more than a decade and affect humans beyond the initial bull’s-eye-type rash and flu-like symptoms. The infection can lead to numerous muscular, skeletal and neurological risks, including arthritis and meningitis. To avoid the initial infections, Jackson said, precautionary measures, such as wearing long pants and long sleeves, tucking pants into socks, avoiding veering off of trails and performing tick checks should be taken.

Beyond adjusting individual, everyday actions and furthering entomologic studies, though, there is more scientific room for improvement.

“The other big wildcard in all of this is how humans respond to the landscape. We’ve been figuring out how ticks and their hosts respond to the landscapes, and we’re now trying to pursue, by partnering with social-scientists, how people respond to different landscapes,” Ostfeld said.