The Great American Tick Invasion

Kevin Loria

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After spending mornings exploring the fields, forests, and gardens of their outdoor classroom just north of New York City, the students and teachers at Little Leaf at Andrus-on-Hudson nature school perform an essential task: the tick check.

The preschoolers sit in a circle on the ground and sing a song about ticks (“Tick, are you in my armpit? Tick, are you in my ear?”) while teachers inspect them one by one, examining their hair and checking behind their knees. They’re looking for deer ticks, which can spread Lyme disease and other illnesses, and are sometimes as small as a poppyseed.

Parents are also encouraged to apply insect repellent to their children before school and do another tick check after school. For added protection, Theresa McCaffrey, Little Leaf’s founder and director, had the perimeter of the garden classroom sprayed with the pesticide permethrin.

All of that might seem like an awful lot of work for a day outside in a grassy suburb. But for millions of Americans, it has become a necessity of daily life.

Disease-carrying ticks, found in all 50 states, have significantly increased their geographical range in the past 15 years, showing up in new places nearly every year and multiplying quickly.

Tick experts in the Northeast have stories about places so infested with ticks that they’re hesitant to name them, not wanting to brand a place as “Tick Heaven.” A Long Island entomologist recalled finding 250 ticks on a single bush. Last year a report from the Centers for Disease Control and Prevention showed that the number of tick-borne diseases more than doubled between 2004 and 2016.

Scientists are testing new approaches that may help curb the explosion of tick-borne illnesses, such as Lyme disease and babesiosis. But there are no large-scale tick-control solutions demonstrated to work, according to Richard Ostfeld, Ph.D., a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, N.Y. In the meantime, people are left to protect themselves against the serious threat of disease using the same precautions taken at the Little Leaf school.

Thomas Mather, Ph.D., director of the University of Rhode Island’s Center for Vector-Borne Disease, has been studying ticks since 1983. He’s known as “The Tick Guy,” and says that over the years he may have collected more black-legged ticks than anyone. The recent rise in tick populations is something Mather has observed firsthand. “If people could just see what I’m seeing,” he says, “they would never go outside.”

A Growing Epidemic

In a recent nationally representative survey of 2,052 Americans by Consumer Reports, 4 in 10 said they had experienced a tick bite. But many more are bitten without ever realizing it. Today, the CDC estimates that there are about 300,000 new cases of Lyme disease in the U.S. each year, most of them unreported.

And Lyme is just the best-known tick-borne illness. At least seven new diseases spread by ticks have emerged since 2004. (See “How a Tick Bite Can Affect Your Health.”) Some can be fatal if not caught early.

Ticks aren’t the only disease-spreading pests on the move. A study published in March predicts that as the world warms, a billion new people could be exposed to mosquito-borne diseases such as Zika, dengue, and chikungunya between now and 2080.

When disease-carrying mosquitoes reach a new area in the U.S., there are standard public health responses, including population control methods, with cities, towns, and counties conducting mosquito abatement campaigns. But when ticks move in, you’re often on your own.

And the problem shows no sign of abating: “The continued spread of ticks, the discovery of new tick-borne pathogens, and the spreading outbreak of human disease is a near certainty,” the Tick-Borne Disease Working Group, appointed by Congress, wrote in a report in 2018.

Yet tick-borne diseases have been underrecognized and vastly underdiagnosed. Funding for treating and especially preventing them is “orders of magnitude lower” than it is for other public health threats, the authors wrote in their report. A big part of the problem is that we don’t understand ticks as well as we do other disease-spreading pests.

“Most tools for control have been developed for mosquitoes, and ticks are very different organisms,” says Adriana Costero-Saint Denis, Ph.D., a vector biology program officer at the National Institute of Allergy and Infectious Diseases. “Research on ticks is lagging a bit behind.” And scientists are still discovering new illnesses spread by ticks that we don’t yet understand. 

A Mysterious Allergy

Ten years ago, researchers led by Thomas Platts-Mills, M.D., Ph.D., at the University of Virginia were just starting to learn that bites from Lone Star ticks were somehow causing a mysterious and potentially life-threatening allergy to red meat.

They’d been trying to explain why certain cancer patients were reacting poorly to a drug known as cetuximab. At the same lab, they’d been working to figure out what was causing a strange allergic reaction to red meat, which had been observed in a number of patients.

Platts-Mills and colleagues traced the drug reaction to a sugar (known as alpha-gal) found in animal products, which ended up in the medicine because it was produced using cells derived from mice. That was the first clue: The people allergic to cetuximab and to red meat were allergic to the same thing—alpha-gal.

What’s more, the people having adverse reactions to the drug and to red meat were all from the same Southern states. The question was why people in these places had all developed this unusual allergy, which at the time had not shown up elsewhere in the country.

As the team—based in Virginia—researched the mystery, three of the scientists themselves developed an allergy to red meat. And they realized they had something in common: They had all been bitten by ticks in the weeks or months before developing the allergy. They started asking patients allergic to alpha-gal about their own experiences with tick bites, and they soon saw that CDC maps showing the geographic range of Lone Star ticks overlapped exactly with the locations of patients reacting to alpha-gal.

By studying a cancer drug, they had inadvertently stumbled across a new tick-borne malady—one unlike any of the other diseases ticks were known to spread. 

“At the time, we didn’t know this thing was going to become huge,” says Scott Commins, M.D., Ph.D., a member of the original research team. They knew of just a few dozen cases then. Now, he says, there are more than 5,000 people with these allergies—and still no known cure or even explanation of why the phenomenon is triggered by tick bites. Stranger still, other species of ticks are somehow causing people to develop similar allergies to red meat on the other side of the world, in places such as Australia, South Africa, and Sweden.

The Diseases They Spread

Lone Star ticks have traditionally lived in the Southeast, but as the climate warms they’ve been spreading. They can now be found as far north as Maine. In addition to the meat allergy, Lone Stars carry Bourbon virus, Heartland virus, Southern tick-associated rash illness, and the pathogens that cause the bacterial infections ehrlichiosis and tularemia, which is so infectious it’s considered a potential biological weapon.

Eastern black-legged ticks, known as deer ticks, are expanding their range, too, bringing Lyme disease as well as babesiosis, Powassan virus, and more. So are dog ticks, which can carry the potentially deadly Rocky Mountain spotted fever, and Gulf Coast ticks, the vector for a milder illness called Rickettsia parkeri.

In 2017 researchers first reported spotting the invasive Asian longhorned tick in the U.S., after discovering hundreds of the pests on a New Jersey sheep, and hundreds more in its paddock. These ticks can essentially clone themselves, reproducing asexually and laying between one and two thousand eggs at a time. They have now been found in at least nine states. While there’s no evidence that this tick species is spreading disease here yet, in East Asia it has been known to cause several illnesses, including a deadly hemorrhagic fever.

“On the longhorn we still haven’t identified any pathogens, but I don’t see why we wouldn’t eventually—I think it may be a matter of time,” says Maria Diuk-Wasser, Ph.D., an associate professor in the department of ecology, evolution, and environmental biology at Columbia University who has been studying the longhorned tick’s invasion of Staten Island, N.Y. “It can basically invade anywhere.”

It’s quite likely, Ostfeld says, that the rates of tick-borne disease will continue to rise. Along with the warmer weather, which gives ticks a longer active season, environmental changes have led to growing populations of mice and deer, which carry the ticks that feed on them, helping the ticks to spread.

One frustrating problem, according to Ostfeld, is that even interventions that kill large numbers of ticks—such as spraying lawns with insecticides—don’t seem to lower rates of tick-borne illness.

And even if we had a better understanding how to kill ticks, there’s currently no national surveillance system tracking where ticks are spreading disease. CDC experts say there are ongoing efforts to improve surveillance, but it will be hard to coordinate a public health response to tick-borne illness before a surveillance program exists.

Nationwide, we need “to understand the geographic distribution of infectious ticks in order to understand the spread of disease and predict where people are at risk,” says the Tick-Borne Disease Working Group’s report. But there are still “significant gaps in information.” 

Until a more organized public health response emerges, taking the steps that McCaffrey’s preschoolers do every day can go a long way. (See “How to Protect Against Ticks,” below.) Experts say these measures offer fairly effective protection on an individual level, although they haven’t been enough to stop the spread of disease. Even in areas where awareness and vigilance are relatively high, tick bites are still common. 

Fighting the Fight

Some communities that have been struggling with ticks the longest are reaching for more innovative fixes.

On Shelter Island in New York, a large nature preserve, marshes, and forests full of oak and beech trees have long made the island a haven for ticks. Residents there are so familiar with tick-borne illness that locals say doctors will consider ticks as the cause for nearly any malady, says Jim Bevilacqua, M.D., chairperson of the town’s Deer and Tick Committee.

Years of attempts to persuade people to take steps to protect themselves haven’t necessarily stopped the spread of these illnesses, so the goal now is to try to get the deer population under control, Bevilacqua says. With fewer deer, the hope is that there will be fewer ticks.

In Dutchess County, N.Y., the heart of the Lyme epidemic, The Tick Project—co-led by Ostfeld—is testing a pesticide spray made from a tick-killing fungus and small bait boxes that can apply a drop of the pesticide fipronil to mice. If the new spray, the bait boxes, or the two combined successfully reduce tick-borne disease when deployed at the neighborhood scale, it will be a first.

To make a dent in the problem, efforts to control deer and other host populations will probably need to be combined with new types of pesticides, Diuk-Wasser says. In some places people prefer to use products that are marketed as organic or natural, she says, but experts say many of these products simply don’t work. Whether or not scientists can develop effective “natural” pesticides that are then widely adopted, people will still need to protect themselves on an individual level because none of these strategies alone will wipe out tick-borne illness. “There’s no magic bullet,” she says. 

Even if those remedies are effective at a local level, experts say other interventions—some requiring millions of dollars in public investment—are also needed. For Lyme, it might be possible to introduce a vaccine.

(A previous vaccine was discontinued because of a lack of demand and reports of side effects such as arthritis, though research showed that arthritis wasn’t in fact more common in people who had been vaccinated.)

Scientists are also working on ways to edit tick genes so that they can no longer spread disease, though such strategies are nowhere near ready for public use.

In the meantime, ticks will continue to spread and new tick-borne diseases will continue to emerge, often before we fully understand how they work or how they should be handled.

Commins says that in the back of his mind, the concern isn’t just that we’re short of solutions for diseases like babesiosis, the hundreds of thousands of Lyme infections every year, and more. It’s that we still haven’t even begun to grasp the extent of the problem. The fact that scientists are just now discovering that ticks can spread an allergy, for example, suggests that “there are perhaps other things that tick bites can do that we don’t quite recognize yet,” he says. “There may be more to the tick bite story than we realize.”

How to Protect Against Ticks

1. Before You Go Outside

Use one of CR’s top-rated insect repellents to cover your exposed skin. You can also use clothing treated with the insecticide permethrin. Wear long sleeves and pants, and tuck your pants into your socks.

2. When You Get Inside

Toss your clothes in the dryer on high for 10 minutes to kill ticks that may be hanging on. The CDC also recommends taking a shower to wash off unattached ticks. Do a thorough body check, especially in places where ticks tend to attach themselves, such as inside the bellybutton, between the legs, in and around the ears and hair, and the back of the knees.

3. If You Find a Tick

Remove it using a fine-tipped pair of tweezers, the CDC says. Grasp the tick as close to the skin as possible and pull straight upward steadily—don’t twist or jerk your hand. Ticks tend to crawl around on skin before they find a place to attach, so you might be able to find a tick before it bites. The longer they’re attached, the more likely they are to transmit disease. For example, a tick is usually attached for 36 to 48 hours before it transmits Lyme disease.

Editor’s Note: This article also appeared in the July 2019 issue of Consumer Reports magazine.

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