JUDY WOODRUFF: The arrival of spring is a most welcome sight to many of us, but it also brings a serious health problem, ticks. They can lead to Lyme disease in humans, which can be a serious chronic condition.
Many suburban areas are trying to figure out just how to deal with an increasing number of ticks, which some blame on the growing population of deer in the U.S.
Researchers are enlisted in this battle as well.
Miles O’Brien has the story for our weekly segment on the Leading Edge of science.
And a warning: Some of the images in this story might disturb some viewers.
MILES O’BRIEN: This English manor in the woods near Boston is Denny Swenson and Wynn Swenson’s dream house. When they moved here 10 years ago, they were thrilled to see a lot of deer.
DENISE SWENSON, Local Activist: And it was so exciting, because they’re such beautiful animals. They seemed harmless. Wow, we felt like we had arrived.
MILES O’BRIEN: But, today, she is a more than a little wary of the deer. In fact, she believes controlling their numbers is the only practical way to stem the spread of Lyme disease. Humans are infected with Lyme from tick bites, and ticks like to feed on deer.
DENISE SWENSON: There’s a trail there that the deer love.
MILES O’BRIEN: This is deer country here?
DENISE SWENSON: Yes, yes. We have tons of deer.
MILES O’BRIEN: The state says that there are about 85 deer per square mile in the adjacent 7,000-acre Blue Hills Reservation; 10 per square mile is considered a density that could reduce the spread of Lyme.
Deer were hunted nearly to extinction a century ago in the U.S. Today, thanks to legal protection and regulated harvests, the deer herd nationwide has exploded to more than 30 million. This creates a host of problems, including more than a million deer-car collisions each year in the United States.
Suburbia offers the perfect habitat for deer to flourish, no human hunters or animal predators and a bounty of food.
DENISE SWENSON: They’re coming all the way up to the front door to eat. They’re really hungry, so they kind of need the rhododendrons as much as I do.
MILES O’BRIEN: Yes. This is kind of like the drive-through of a deer, right?
DENISE SWENSON: Yes. This is the drive-through for them, yes.
MILES O’BRIEN: Lyme is an infectious disease caused by a bacterium transmitted to humans by the bite of infected blacklegged ticks.
Symptoms often begin with a distinctive bullseye rash and evolve into various neurological problems, including facial palsy, severe headaches, muscular aches, and sensitivity to light.
Without antibiotic treatment, Lyme disease can lead to permanent motor, sensory and cognitive impairment. It is the most common tick-borne disease in the Northern Hemisphere. There are an estimated 300,000 cases a year all across the U.S. Both Denny and Wynn have had multiple cases of Lyme disease.
DENISE SWENSON: Oh, I will never forget those headaches. I will never forget the pain sort of sweeping around my body. I felt like I was being invaded by some crazy thing.
MILES O’BRIEN: The more she asked around, the more she got scared.
DENISE SWENSON: We did a neighborhood survey, and 30 households responded, and we found 30 cases of Lyme disease.
MILES O’BRIEN: You basically have a public health crisis here.
DENISE SWENSON: Yes, these are epidemic level numbers.
MILES O’BRIEN: A former journalist, Denny Swenson started researching.
The Lyme disease bacterium lives inside white-footed mice, the so-called reservoir. Ticks that bite the mice become infected propagators, or vectors, of Lyme. She quickly, concluded reducing the population of mice, or the ticks themselves, using chemicals, is neither practical nor prudent for the environment.
But what about targeting deer?
SAM TELFORD, Tufts University: There’s no animal as abundant as deer in these habitats, and these ticks do seem to like deer.
MILES O’BRIEN: Sam Telford is a professor of infectious disease and global health at Tufts University’s Cummings School of Veterinary Medicine. We met at a hunter inspection station during deer season in Webster, Massachusetts, 60 miles southwest of Boston.
SAM TELFORD: Do you mind if I check for ticks?
If I were to be here 20 years ago at the check station, at this check station, I could look all day and maybe find two or three ticks. Now, in the course of two hours, we have gotten probably 50 ticks off a deer.
MILES O’BRIEN: Fortunately for the deer, they are not susceptible to Lyme disease.
Telford’s fieldwork might make you squirm a little bit. He harvests thousands of ticks to study later in his laboratory. Lyme is just one of more than a dozen human diseases and infections spread by ticks. They are, by far, the biggest disease vector in the U.S.
Telford showed me a tube filled with two fully engorged female deer ticks.
Those are fully fed?
SAM TELFORD: These are fully fed.
MILES O’BRIEN: That’s all blood in there, right?
SAM TELFORD: That’s the end result of feeding for seven days. Each one of those will lay 2,000 eggs.
MILES O’BRIEN: So even though mice might be the Lyme disease bacterium reservoir, Telford believes controlling the deer population is the key.
SAM TELFORD: If you were trying to intervene to try to control the force of transmission of the agent of Lyme disease, what do you go after, something small or something that’s far more limited in numbers, but produce the ticks?
MILES O’BRIEN: In the late 1980s, he ran an experiment to test his theory on a small, isolated Cape Cod peninsula. A sharpshooter reduced the deer population from about 50 to fewer than eight. The numbers of ticks dropped precipitously, by 80 percent.
Ever since then, he has tried to convince people who live in suburban communities overrun by deer to take similar action.
SAM TELFORD: The reality is, some communities won’t tolerate hunting, and so there have to be alternatives.
MILES O’BRIEN: At the National Institute of Standards and Technology in Gaithersburg, Maryland, they’re trying birth control. The 600-acre campus is home to 180 deer. They are everywhere.
ANTHONY DENICOLA, White Buffalo Inc.: National Institute of Standards and Technology: We have created a monster. There’s no doubt. And it’s just whether or not we contain it in a realistic timeline, based on the growth of these deer populations and the ever-increasing conflicts with people.
MILES O’BRIEN: Wildlife ecologist Tony DeNicola runs a nonprofit organization focused on managing white-tailed deer herds in suburban environments. After they were tranquilized at NIST, the deer were surgically sterilized by veterinarians, 61 does over 10 days.
ANTHONY DENICOLA: Sterilization has the benefit of the social support of much of the public, eliminates a lot of the controversy around lethal programs. But, as you would expect, it is far more work in order to handle these animals, and you don’t get the immediate population impact.
MILES O’BRIEN: The Humane Society of the United States is a big advocate of alternatives to conventional hunting. That’s what they’re doing 20 miles north of New York City in the village of Hastings-on-Hudson.
KALI PEREIRA, The Humane Society of the United States: This is our third capture season for this project.
MILES O’BRIEN: Kali Pereira is the senior deer program manager at the Humane Society.
KALI PEREIRA: We’re using a product called PZP-22 to address population control in an urban environment that hunting is not an option for.
MILES O’BRIEN: PZP-22 is a birth control vaccine that lasts for 22 months.
About 70 females in the herd here are on this birth control drug. It’s a first-in-the-nation experiment that is a labor-intensive, ongoing effort. It requires patience.
KALI PEREIRA: Usually, these projects take you a minimum of five to 10 years before you see true population plateau and reduction.
MILES O’BRIEN: Slow as the approach is, it doesn’t draw controversy, which is what happens when the state of Massachusetts allows deer hunting with shotguns in the park near the Swenson house.
In two seasons, they have killed 122 out of an estimated 850 deer. Sam Telford says the ideal size of the Blue Hills herd is about 100. But is that a realistic goal?
Stephanie Boyles Griffin is the senior director of innovative wildlife management and services with the Humane Society.
STEPHANIE BOYLES GRIFFIN, The Humane Society of the United States: Attempting to reduce deer populations to reduce the transmission of Lyme disease has not been shown to really be effective. You would have to cull deer populations so low, and that’s really just not achievable in a lot of these urban systems.
MILES O’BRIEN: In Denny Swenson’s neighborhood, most people are committed to thinning the herd, but there is some ambivalence.
DENISE SWENSON: Killing them wasn’t my first goal at all, and I’m so heartbroken that we have to. But for the health of the deer and the health of the forest and the health of the people that visit the forest, we need to manage this problem.
MILES O’BRIEN: The explosion of the deer population in suburbia and the rapid rise of Lyme disease are warning signs of an ecosystem out of balance. The hunt for solutions won’t be cheap, easy or fast.
Miles O’Brien, the PBS NewsHour, Milton, Massachusetts.