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PRI's Environmental News Magazine

Lyme Disease Surge

Air Date: Week of September 1, 2000

Lyme Disease has risen dramatically in the past few years. So the tiny creature that’s responsible for infecting people, the deer tick, has earned an infamous reputation. But the disease doesn’t really begin with a tick bite. Ecologists say the real culprit is an environment that’s friendly to both the ticks and animals they feed on. Living On Earth’s Diane Toomey reports.

Transcript

CURWOOD: This is Living on Earth. I'm Steve Curwood. It's the scourge of the suburbs, the price you may pay for a walk in the woods. Lyme Disease is a tick-borne illness that can cause flu-like symptoms and fatigue. If left untreated it can lead to brain damage. The incidence of Lyme Disease is on the rise, and in the Northeast and upper Midwest, where most of the disease-spreading ticks live, long pants and full body checks are now a summer regimen. Now there is new research that takes an ecosystem approach to combating the illness. It works by preventing the disease from being spread in the first place. Living on Earth's Diane Toomey reports.

DANIELS: I would like to know what a tick thinks.

TOOMEY: Fordham University ecologist Tom Daniels says researchers understand very little about the tick lifestyle. Although he has years of data looking at how tick numbers fluctuate with environmental conditions, that's just scratching the surface, he says. We do know a tick makes use of a number of different animals as hosts, a polite term to describe where it gets its blood meals.

DANIELS: This thing lives for two years and most of the time it's waiting for something to come by. And so, I would like to know what dangers it encounters. Why it chooses not to get on some hosts as opposed to feed on others, but to know why we find them in some areas of the woods and not others.

TOOMEY: For now, Daniels is making use of the tick knowledge he does have.

(Tape tears)

TOOMEY: Daniels is suiting up to go tick hunting. He wraps masking tape around the ankles of his jumpsuit so ticks can't jump in. Then he heads out into a patch of woods on private property in Westchester County, New York, an area where Lyme Disease is endemic. This tony neighborhood, just outside New York City, is a prime example of why the illness is on the rise. As more and more people move into suburbia, they move into the natural territory of deer ticks, the kind that spread Lyme Disease. What's more, suburbia, brimming with ornamental plants and full garbage cans, attracts the mice and deer that are the major hosts for deer ticks. And more hosts means even more ticks.

(Footfalls)

TOOMEY: Daniels drags a white corduroy cloth behind him. August marks peak season for larvae, the beginning stage in the troika that make up a tick's lifestyle after it hatches. Daniels wants to estimate how many larvae are on this property. A few of them have grabbed onto the drag cloth. To the untrained eye, they look like little more than specks of dirt.

DANIELS: So far we've got three. Now look, just by handling the cloth, I've got two of them on my hand. And that's just one of the bonuses of doing tick work.

(A lint roller sweeps)

TOOMEY: Daniels meticulously collects the larvae with a lint roller. This head count is part of an effort to gauge the effectiveness of a federally-funded tick reduction project. Although many people in Lyme Disease country would like to see a reduction in the exploding number of deer, Daniels' experiment is being done in the spirit of, "If you can't beat 'em, feed 'em." He stops at a large metal box with troughs on either side.

DANIELS: This reservoir here is filled with about 200 pounds of corn. Corn spills out into these side troughs. The deer are attracted to the corn, and when they come in to feed on it, they have to rub their head and neck against these treated rollers to get at the corn.

TOOMEY: The rollers apply a pesticide to the deer's neck and shoulders, where ticks are most likely to feed. There are two dozen of these feeders set up in a two square mile area here. Even if it proves effective, Daniels knows this method isn't a panacea.

DANIELS: Not everyone will want a feeder, and it does take some maintenance. But if it shows, if it proves to have some impact, and you can envision entire neighborhoods, perhaps, setting up a series of feeders, it wouldn't have to be on every property.

TOOMEY: There is a lot of Lyme Disease in Westchester, but it's a county further north than New York that wins the prize for greatest number of Lyme cases in the country. And Duchess County where ecologist Rick Ostfeld keeps track of Lyme Disease by keeping tabs on the white-footed mouse. Here's why: when a tick hatches, it doesn't have Lyme Disease. While people can blame ticks for their infection, the ticks can blame the mice.

OSTFELD: White-footed mice are the main host for the larval stage of the tick, and the main source in the environment where the tick picks up the Lyme Disease. The more mice there are, the more ticks get to feed on mice, the more of them get infected with Lyme. And then the higher the number of infected ticks there are one year later when the nymphal stage feeds, and that's the stage that infects most people.

TOOMEY: No one is sure why white-footed mice, compared to other host animals, have such a high concentration of Lyme bacterium swimming in their bloodstream. What is known is that a tick has about a 90 percent chance of getting the bacterium after it bites one of the ubiquitous white-footed mice. So Ostfeld, as part of his research, monitors mice populations.

(Clicking)

OSTFELD: Oh, boy, here we have a flea colony. If I were a mouse, I wouldn't want to live there either.

TOOMEY: Ostfeld checks in on the wooden mouse nesting boxes he and his team have attached to some trees in this oak forest. This property belongs to the Institute for Ecosystem Studies, an almost 2000-acre independent research center that serves as Ostfeld's laboratory. By tracking the whereabouts of newborn mice, Ostfeld hopes to find out which elements of the forest influence the mouse population here. He opens up another nest box.

(Hinges creak)

OSTFELD: Nobody home. And that's going to be the way it's going to be, because we have low mouse density this year. Because last year was a year of zero acorn production, so the mice didn't have a winter food supply, and they're very low this summer.

TOOMEY: Ostfeld theorizes that acorn production can be used as a kind of leading indicator for Lyme Disease. For instance, two years ago acorn production soared. That led to lots of mice last year, and according to the theory should predict more infected ticks this year. Ostfeld opens up another nest box. This one yields a single mouse.

OSTFELD: Let's just see if we can find some ticks. It's a clean mouse. (Snips) Ah, here's a tick. Here's one on the tip of the ear. It's a little, tiny bump that you can barely see.

TOOMEY: Ostfeld says another factor that probably influences Lyme Disease risk is the level of biodiversity in a given area. Lots of different animals mean mice have to deal with predators and competitors, so their numbers drop. What's more, greater biodiversity might produce something called the dilution effect. If a tick has lots of menu choices -- birds, chipmunks, squirrels -- its chances of being infected with Lyme drop, since those animals don't transmit the bacterium as efficiently as the white-footed mouse.

TOOMEY: To test the theory, Ostfeld has sent research assistant Brian Allen out to collect ticks from different parts of Duchess County, from forested plots dozens of acres in size to small fragmented pieces of land called back yards.

ALLEN: People have cooked for me and people give me beers and sodas and everything at the end of the day.

TOOMEY: When he brings the ticks back to the lab, Allen must grind them up so they can be analyzed for the presence of the Lyme bacterium.

(Grinding)

ALLEN: A properly ground tick should explode on contact between the grinder and the side of the vial.

(Grinding)

TOOMEY: The data from the study haven't been analyzed yet. But if the biodiversity theory holds, we may, by creating more and more suburban landscapes, be inadvertently increasing our risk of Lyme Disease. For Living on Earth, I'm Diane Toomey.

 

 

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