What You Need to Know About Ticks

A few weeks ago, on a pleasantly cool day, this reporter and his dog, an Alaskan malamute named Bear, headed for a small set of trails in an area of woods not far from the New York-New Jersey border. With bicyclists plying their way on the shoulder of a nearby highway and the Hudson River rushing along beyond the wooded landscape, man and dog walked along the well-maintained trails, yielding to other visitors and trying to stay away from the tall grass.

There used to be a commonly held belief that ticks couldn’t survive below a certain minimum temperature, preventing their spread to northern climates. Now researchers are rethinking the relationship between tick populations and temperature. Photo credit: Uwe Mäurer

Memories of the day were somewhat dampened after returning home. Bear, whose deep malamute hair is a jungle of fluffiness, brought home an intrepid hitchhiker. Crawling in that furry maze and thankfully not attached to his skin, was a tick, no doubt on the hunt for some dog blood—or human blood, for that matter. Another one was found crawling nearby. This episode plays out across the U.S. and the rest of the world on a regular basis.

According to experts in the field, ticks have gone through some changes over the past few years.

“I think one of the biggest concerns that you see within the published literature for ticks is that ticks’ geographical regions are expanding,” said Dr. Janet Foley, a professor and researcher at the School of Veterinary Medicine at the University of California, Davis. Foley, who studies the ecology and epidemiology of infectious diseases, also serves as co-director of the Center for Vector-Borne Diseases, an institution on the frontlines of tick and mite research.

“Clearly ticks are expanding farther north,” she said. “[W]e’re finding a lot of tick species moving into new areas. And a lot of that has to do potentially with climate change [and] animal husbandry practices if we’re cutting forests or recreating grasslands … So as a whole ticks themselves are really becoming an emerging problem, not that they always weren’t anyway, but they are getting worse.”

Foley said the expansion of their range has brought them into Canada and she called some of them “very, very aggressive human biters” that can potentially transmit disease.

The Centers for Disease Control & Prevention (CDC) lists on its website the tick species in North America, including the American dog tick, blacklegged tick, brown dog tick, Gulf Coast tick, lone star tick, Rocky Mountain wood tick and western blacklegged tick. To the untrained eye, these insects may seem invisible (in the case of poppy-seed-sized nymphal ticks) or indistinguishable (small insect with eight legs—must be a tick). Encounters with a particular species depend on where one lives and these geographical ranges may be in the process of changing.

For example, the CDC reports that the American dog tick—perhaps the species found on Bear—is found on the East Coast, Midwest and parts of the West Coast. This particular tick can transmit Rocky Mountain spotted fever. Another candidate for Bear’s tick would be the blacklegged variety, also known as a deer tick. This is the species that can spread Lyme disease, which the CDC states can cause fever, headache, fatigue and a skin rash. Antibiotics can be used to treat the disease.

Foley and her colleagues are actively involved in tick-related research, both in the laboratory and out in the field. Her particular interest lies in ecology and how tick-born disease and mange, which is caused by mites, take advantage of complex, natural communities.

“What we are doing is diagnostic testing, so surveillance, collecting ticks to see if they are currently infected with a pathogen,” she said. “We dissect them. We remove the DNA, [and] do diagnostic testing that way … Ticks are notoriously difficult to work with in the lab because they have such a slow life cycle. The western blacklegged tick can take three years to go through its whole life cycle and that’s a long time to keep them.”

According to Foley, there used to be a commonly held belief that ticks couldn’t survive below a certain minimum temperature, preventing their spread to northern climates. The line seemed to be drawn along the southern border of Canada, although exceptional populations abounded.

Researchers, including Foley, are now rethinking the relationship between tick populations and temperature. “[W]e are seeing them north of [the U.S.], so the question is, it’s not so much that it gets too cold once, but maybe the average cold is less cold than it used to be,” she said. “Or another thing might be and I think this is more likely … what if it warms earlier in the spring? What if it actually gets just as cold as it used to but starts giving them a little more time in the spring to come out? Then they don’t have to stay in hibernation as long.”