As Lyme Disease Cases Spike In Virginia, DC, Researchers Offer Sly Solution

WASHINGTON, DC — As you enjoy a leisurely walk in the woods or fields this summer, nearly invisible ticks may be waiting in the grass to make you a meal and potentially pass along dangerous pathogens. Lyme disease, one of the most common tick-borne illnesses, is on the rise — the Centers for Disease Control and Prevention say there may be as many as 300,000 cases of the infection per year in the United States, though many of these could go undetected.

In 2015, according to the most recent data, more than 28,000 people had confirmed cases of Lyme in the country. Virginia reported 1,102 confirmed infections in 2015, about 25 more than the previous year, and nearly four times the 274 confirmed cases a decade ago. That puts the state's rate of infections at 13.1 per 100,000 people. In Washington, D.C., there were 78 confirmed infections in 2015, compared with 10 a decade earlier, for a rate of infection of 11.6 per 100,000 people.

In other parts of the country, even more cases were reported. Pennsylvania was the hardest-hit state, with 7,351 cases in 2015, compared with 4,287 a decade earlier. That's a rate of 57.4 infections per 100,000 people. And adjacent Maryland reported 1,249 confirmed infections in 2015, about 100 more than the previous year, although far less than the 2,576 confirmed cases a decade ago. That puts the state's rate of infections at 20.8 per 100,000 people.

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But a new study may point to a promising approach to fighting the spread of the disease and help explain why it has been on the rise. And it all comes down to foxes.

Tim R. Hofmeester, a graduate student at the Netherlands' Wageningen University, led a recently published study that exposes humanity's part in driving up the spread of tick-borne illnesses like Lyme. By fracturing habitats and disrupting ecosystems, humans have allowed the ticks that feed on wild mice to flourish — and these intrusions are coming back to bite us.

Hofmeester and his team monitored 20 different outdoor locations across the Netherlands, tracking predators, mice and the ticks that feed on them. The result is that as predatory animals like foxes proliferate — causing the tick-bearing rodents to scurry and hide in their burrows — fewer of the disease-carrying insects will infest our forests and fields.

But in places where predators are scarce, the ticks run wild.

"The results suggest that predators can indeed lower the number of ticks feeding," the authors write, "which implies that changes in predator abundance may have cascading effects on tick-borne disease risk."
This study shows an effect that scientists had long suspected might occur, but they previously lacked the evidence to prove it.

The authors advise that the finding "calls for the appreciation and protection of predator species such as red fox," which are frequently harmed by human populations.

Perhaps surprisingly, the study found that an increase in the predator population doesn't actually decrease the amount of mice in a given location, which would seem to be the most natural explanation for the reduction in the tick population. Instead, foxes keep the ticks away through other means.

"Many prey species show decreased movement and increased refuging behavior in the presence of a predator," the authors write. In other words, the mice are too busy hiding from foxes to end up as tick food.
These findings are particularly important in light of the rapid increase in rates of Lyme disease and other tick-borne disease, as the CDC has reported.

“Since the late 1990s, the number of reported cases of Lyme disease in the United States has tripled and the number of counties in the northeastern and upper Midwestern United States that are considered high-risk for Lyme disease has increased by more than 300%," Research Biologist Rebecca Eisen of the CDC said. "One explanation for this trend is that the ticks that can transmit Lyme disease have expanded their geographic range and are now being found in places they weren’t seen 20 years ago."

Other research suggests that human impacts on the environment are driving up the rates of diseases like Lyme by boosting tick populations. Climate scientists say that as temperatures rise due to global warming and spring comes earlier, ticks have more time to thrive.

“As the climate warms, the ticks become active earlier and earlier in the season," said Richard Ostfeld of the Cary Institute of Ecosystem Studies in New York, explaining part of the recent rise in Lyme disease infection rates.

What this means is that we should expect that our intrusions on natural systems will have unforeseen side effects. If we disturb fox habitats, we leave ourselves more vulnerable to Lyme disease and other tick-based illnesses. Managing our relationship with the environment — even for our own good — calls for a delicate touch.

VIDEO: What You Should Know About Lyme Disease

Photo: US Department of Agriculture