In parks, in backyards, in woods that are lovely, dark, and deep, a many-legged menace now stalks the land. I speak of ticks, and I come bearing absolutely no good news. In recent decades, ticks have made the leap from nuisance to genuine public-health threat: Their numbers are rising. Their ranges are expanding. And the diseases they carry are multiplying. Lyme cases have more than doubled since 2000, in which time scientists have also discovered eight new tick-borne diseases—plus an unusual and potentially dangerous tick-induced meat allergy called alpha-gal syndrome.
“The ticks are winning,” a CDC scientist wrote in a recent paper. To put it even more bluntly, humans are losing and are on the retreat. Ilia Rochlin, a tick researcher at Stony Brook University, told me he stopped hiking in the Pine Barrens of New Jersey after he and his wife came across hundreds and hundreds of newly hatched lone star ticks on a trail several summers ago. And on Long Island, where he lives, “it is impossible to go hiking in most areas,” Rochlin said. “Just because of ticks.”
Tick prevention today is a matter of individual responsibility. If you can’t avoid ’em, you’re supposed to pretreat clothes with the pesticide permethrin, tuck your pants into your socks, and check your entire body for ticks—a real pain, honestly, just to hang out in your backyard. Maria Diuk-Wasser, a tick researcher at Columbia, told me her own family doesn’t always listen to this advice. “I’m like, oh my God, if we don’t even do it here …” The tick problem has reached an inflection point: It is too big to address with personal protective measures alone.
What we need, tick experts now argue, is widespread tick control, akin to mosquito control that has been carried out by state and local agencies for more than a century. Rochlin, who used to work in mosquito control, pointed out that his predecessors in New York were chiefly concerned with malaria. Yes, malaria—now known as a tropical disease—once killed hundreds of New Yorkers every year. In the early 20th century, a massive national mosquito-eradication effort, which led to the CDC’s creation, ultimately expunged the disease from the country. “Compare this huge success story of malaria control in the United States,” Rochlin said, with “this humongous failure to control tick-borne disease.” Today, the number of Americans who contract diseases from tick bites dwarfs the number falling ill from mosquito bites.
To beat the ticks, we need new tools, such as pesticides and vaccines. We need the political will to actually use existing ones, namely, killing deer. We need to make the United States into an environment hostile to ticks—something Americans have accomplished once before, just not on purpose.
When the colonists arrived in what would become the United States, they began turning forests into farmland and hunting white-tailed deer, which neared extinction by 1900. This turned out to be an excellent, if unintended, tick-control strategy. It deprived the parasites of habitat and, more crucial, their key host animal. In low numbers, infected ticks crossed over only occasionally to bite humans.
But as farming declined in the 20th century, forests regenerated. Deer populations rebounded, this time without natural predators such as wolves to keep them in check. Ticks flourished too. In recent decades, two formerly obscure tick species have enormously expanded their reach: the black-legged or deer tick, which is best known for spreading Lyme, and the lone star tick, best known for causing alpha-gal syndrome. (The lone star tick, at least, seems to be reclaiming its former range; it was likely in modern-day New York in the 1700s, before disappearing to the south and not reappearing this far north again until the 1990s.) The two species collectively carry a number of other, lesser-known pathogens, too, including anaplasmosis, babesiosis, Powassan virus, Ehrlichia, and Bourbon virus. These diseases likely once circulated primarily among animals, but they are now spilling over into humans because of the sheer number of ticks that are out and looking for blood.
No one thinks we should solve our modern tick problem by chopping down all of the trees. But everyone I spoke with agreed: We have to do something about the deer. “Deer are the key.” The “common denominator.” The “crux of the issue.” The “main driver of all that is evil today in the northeastern United States.”
That last quote is from Sam Telford III, an epidemiologist studying tick-borne diseases at Tufts University, who calls himself “the nation’s biggest advocate for killing deer.” Ticks rely on the blood of deer to reproduce, his argument goes. A single deer, Telford told me, can feed 1,500 female deer ticks, each of which can lay 2,000 eggs. That’s 3 million deer ticks per deer, over one breeding season—even higher for the more fecund lone star tick. Killing deer is therefore “the biggest bang for your buck,” he said. This strategy was most convincingly implemented in 1997 on Monhegan Island, off the coast of Maine, where residents fed up with Lyme disease hired a sharpshooter to cull all of the deer. After that, Lyme virtually disappeared from the island.
We know very well how to kill deer (“Rifle,” Rochlin deadpanned), but doing so is unpopular. It makes animal-rights activists livid, the general population squeamish, and even hunters unhappy about competing for fewer deer. Lately, though, Telford said, people have become desperate enough about ticks to reconsider. On Martha’s Vineyard, which has come under recent siege by lone star ticks, hunting is having a resurgence. The island extended its hunting season and plans to build a new deer-processing facility.
Hunting can accomplish only so much, though. It can reduce the density of deer from 70 to 40 per square mile, but breaking the disease-transmission cycle requires going below 10, according to Kirby Stafford III, an emeritus chief scientist at the Connecticut Agricultural Experiment Station, where his department studied this exact issue. Moreover, hunting in many of the suburbs home to tick-infested deer is impossible because of all the people who live there, too. On New York City’s Staten Island, where hunting is illegal, the city has been giving vasectomies to male deer for the past 10 years. The deer population has fallen by nearly half, but the tick story is more complicated; while tick numbers have gone down, the proportion carrying Lyme has gone up.
An alternative idea: Make the deer themselves tick resistant. A device called the “4-poster” station lures deer with corn as bait, before rubbing permethrin—the same pesticide we humans use—onto the animals as they snack. But that approach has not proved terribly successful. (Too expensive; limited range.) “Not practical,” concludes Stephen Rich, a microbiologist at the University of Massachusetts at Amherst, who has tested these bait stations on Cape Cod and nearby Chappaquiddick Island. Lately, he’s homed in on a different idea: Turn the blood of deer into tick poison, as we already do to dogs. Rich is exploring the use of fluralaner, sold for dogs as Bravecto: He hopes to apply it to captive deer this fall, before expanding to Chappaquiddick next year, where his team will be pouring the fluralaner onto deer that have been tranquilized.
Or perhaps a vaccine could make ticks simply fall off their host. Animals such as rabbits and cattle naturally become resistant to ticks after repeated bites, likely by mounting an immune response to tick saliva; this is the biological basis for anti-tick vaccines that scientists are trying to develop in humans. Durland Fish, a tick researcher at Yale, argues a deer version could be simpler to develop for biological and regulatory reasons. The challenge then becomes how to vaccinate deer. The USDA currently air-drops fish-meal-flavored oral rabies vaccines to raccoons, and researchers are now studying how to similarly entice deer. “I’m like, what kind of deer crack can we put in there?” says Jean Tsao, a tick researcher at Michigan State University who has tested baits locally. Currently, it’s alfalfa, which has not quite hit the “deer crack” threshold.
In speaking with tick researchers, I sometimes got a sense of mosquito envy. “I’m still amazed,” Tsao told me, when she goes to mosquito-control meetings. “They know what size droplet to spray that will be effective as the plane is flying over to kill mosquitoes down below.” They know what time of day to spray and where. And those same conferences discuss all kinds of ideas for new mosquito pesticides, Diuk-Wasser, the researcher at Columbia, said. “But there’s funding to do that,” which is not the case for ticks.
Existing chemicals are very effective at killing ticks, but they are very effective at killing friendlier bugs, including pollinators, too. Scientists are studying how to target their application—to certain habitats or certain times of the year—to minimize harm to other bugs. (Tick researchers I spoke with were largely skeptical of popular natural yard sprays that are derived from essential oils.) And they are searching for more specific alternatives, such as fungi that kill only ticks.
Ultimately, tick control will likely require a combination of strategies, rather than any one magical solution. Hunting, vaccines, and pesticides applied both to deer and in the larger environment could all play some role. When Lyme first appeared in isolation in the U.S., we conceived of it as a medical problem, Fish told me, putting the bulk of public research dollars into medical treatments. But the subsequent appearance of so many novel tick-borne conditions points to a larger ecology problem. Better than finding stand-alone treatments for each of these conditions is preventing Americans from getting sick in the first place—by making ticks less abundant across the land.