LYME DISEASE

Archive: Where foxes thrive, Lyme disease doesn't

John Ferro
Poughkeepsie Journal
  • %22The nature here is terrifying%2C%22 said the wildlife researcher%2C Taal Levi.
  • Taal Levi%27s work is adding to the deepening understanding of how ecology %u2014 and specifically%2C the interplay between wildlife species %u2014 accelerate the spread of infectious disease.

Published Sept. 20, 2012

Taal Levi has studied environments from Brazil to Alaska. But nothing scares him so much as Dutchess County for its abundance of disease-carrying ticks.

"The nature here is terrifying," said the wildlife researcher who studied local woodlands for several weeks this summer. "It's more dangerous to walk around the forest here than it is to walk around the forest in Brazil."

Dutchess County has consistently ranked among the top counties in the nation for per-capita rates of Lyme disease, caused by the bite of the black-legged tick. Levi, a National Science Foundation postdoctoral fellow from the University of California at Santa Cruz, believes that where the population of foxes declines, Lyme disease increases. And contrary to popular wisdom, he thinks deer have little to do with the growing menace of what are also — perhaps unfortunately — called deer ticks.

Levi's work is adding to the deepening understanding of how ecology — and specifically, the interplay between wildlife species — accelerate the spread of infectious disease. Scientists and advocates say that studies like Levi's that seek to stop the spread of Lyme are underfunded and overshadowed by the debate over how to treat chronic Lyme disease, as reported in Sunday's Poughkeepsie Journal.

Taal Levi, a researcher at Cary Institute for Ecosystem Studies, removes a motion sensor camera from a wooded area in Poughquag on Thursday, July 12, 2012. The images captured of large and small mammals near a bait set up are being used in a Lyme's disease study.

According to Levi's theory, foxes are indiscriminate and voracious killers of mice and small rodents. Mice are especially good carriers of Lyme disease because their immune systems don't seem to fight off the pathogen and they don't remove ticks from their bodies well. By comparison, opossums can remove as much as 96 percent of the ticks on their bodies, Levi said.

Levi used statistical data to show that as fox populations went down, Lyme went up. The statistical connection between Lyme and other species wasn't as consistent. The study was published in the Proceedings of the National Academy of Sciences in June.

This summer, he tested his theory at the Cary Institute of Ecosystem Studies in Millbrook. Results are pending.

A coyote roams a small forested area in Dutchess County during the night. This photo was captured by a motion-sensitive camera as part of a study to examine the impact of different predators on the rates of Lyme disease. This photo was taken June 25, 2012.

Levi believes that the return in the Northeast of coyotes in the last half-century, which prey on foxes, is leading to fewer foxes in some areas, and a resulting increase in Lyme.

Just how ticks became more abundant in recent decades is not fully understood. Richard Ostfeld, a disease ecologist with the Cary Institute, said one theory is that ticks were nearly wiped out when forests were clear-cut and converted to agricultural lands in the 18th and 19th centuries.

The ticks that survived, Ostfeld speculates, did so in small refuges on the north shore of Long Island and the shore of southern New England. It is believed that the Lyme disease bacterium — which is not new and genetic signs of which were discovered last year in the frozen body of a 5,300-year-old Neolithic man — persisted in these places as well.

As farming has given way to development, woods have become more abundant. Ticks have followed, supported by rodents and the like whose natural predators have been conveniently eliminated.

"So you have a situation in which the stage is set," Ostfeld said. "The ticks are there. The good reservoir hosts are there. But the pathogen is not there yet. And you need something to bring the pathogen in, because then, the play begins."

Ostfeld speculates that Lyme was transported from the refuges by birds and the ticks that bit them.

Other tick-borne pathogens, which birds do not carry, have advanced more slowly on the backs of small mammals.

Those theories don't explain, however, why the disease has become endemic.

It's one thing to have some mice running around, spreading the Lyme pathogen to a few ticks. It's another thing to have places in Dutchess County where as many as 65 percent of the ticks are infected with the Lyme bacterium.

Those rates have been determined by ongoing Cary Institute studies at 188 sites around Dutchess County.

Field researchers drag canvases across the ground, collect ticks and then test them to determine the infection rates. The study seeks to understand what types of topography are more likely to have a higher concentration of ticks.

When Ostfeld read Levi's statistical analysis, Ostfeld was intrigued and thought Levi could add to Cary's research. Levi placed motion-sensor cameras that captured images of the wildlife in each of the sites.

The early data are startling.

Where Lyme disease infection rates in ticks are lowest, Levi's cameras have documented a clear presence of foxes and, to a lesser degree, bobcats. The low-infection sites have very little coyote activity.

"You don't see this pattern with any other species," he said.

In areas with high rates of infected ticks, it's not as clear what the impacts of foxes and coyotes are. But Levi points out that the data collected by his cameras is being compared with last year's tick-infection rates. Once Cary is done processing this year's infected-tick rates, the patterns should be clearer, he said.

Levi's research challenges the common wisdom that deer are most to blame for spreading Lyme. His statistical analysis showed little correlation between the prevalence of deer and the incidence of Lyme. If that were the case, Levi said, "then why is Lyme disease so relatively rare in Western New York when deer are more abundant than in places here that have lots of Lyme disease?"

One theory is that deer are much better at clearing the Lyme pathogen from their system than mice. The response of various mammals' immune systems to Lyme and other diseases is still being studied.

Other species, such as opossum, are very effective at grooming ticks. To understand this, researchers at Cary placed different species into cages, covered them with ticks, waited for the biting arachnids to jump off and then counted how many survived. Opossums, Levi said, can eat or remove as much as 96 percent of the ticks that land on them.

The risk to humans is when the balance between ticks, their hosts, predators and the surrounding ecology is disrupted. Ostfeld and others have argued that one of the most dangerous consequences of suburbanization is the increase in small patches of forested areas, or forest fragments, where mice thrive and their predators don't.

The research is only just beginning to enter the discussion about Lyme and how to prevent its spread. At a July 31 meeting of the Ulster County Lyme Disease Advisory Committee, New Paltz resident Irwin Sperber referenced Ostfeld's research and called on local governments to find ways to limit development that creates conditions for the spread of Lyme disease.

"There is too much of what we call checkerboard development," Sperber said. "If we want to stop this horrible epidemic, we have to crack down on the kind of irresponsible and unduly accommodating zoning boards that allow for development every which way but loose."

John Ferro: 845-437-4816; jferro@poughkeepsiejournal.com; Twitter: @PoJoEnviro.


About this series

This is the fourth installment in a Poughkeepsie Journal series on Lyme disease. On Sunday, the Journal reported in Part 3 that research into controlling ticks is lagging. Part 1 reported the dramatic rise in Lyme cases, both nationally and locally. Part 2 reported on the controversy surrounding the treatment of chronic Lyme disease. To view previous stories and a replay of an online chat, go to www.poughkeepsiejournal.com/lyme.