Is Killing More Deer the Answer to Reducing Tick Diseases?

So, wouldn’t it be great if we could shoot our way out of those problems? Whitetails especially are key hosts for several tick species, including Lone Star ticks, dog/wood ticks, and the infamous blacklegged tick, aka the “deer tick.”

Deer ticks not only transmit Lyme, but also anaplasmosis, ehrlichiosis, babesiosis, and Powassan diseases—as well as alpha-gal syndrome, the incurable red-meat allergy that permanently eliminates beef and venison from victims’ menus. Even though deer don’t carry Lyme disease in their system, and typically don’t host deer ticks during their infectious nymphal stage, adult deer can sustain hundreds of hitchhiking deer ticks. As deer disperse or move about their home range, they spread adult deer ticks as they drop off to lay their eggs below leaf litter in forests, farmland woods, and backyard woodlots.

After deer tick offspring hatch and start growing, they can contract and spread Lyme disease and other ills to humans. Depending on the area, roughly 25% to 50% of deer tick nymphs carry Lyme disease.

Deer are also major hosts of the Lone Star tick during all of its life stages. These ticks are notorious for spreading tularemia (rabbit fever), ehrlichiosis, heartland virus, bourbon virus, and the alpha-gal allergy. And because deer also carry dog ticks, aka wood ticks, they help spread Rocky Mountain spotted fever, widely considered the U.S.’s most serious tick-borne disease because victims often require hospital care.

Uncertain Disease Links
Therefore, as whitetail populations increasingly live amongst people, tick-borne ailments remain common. The Centers for Disease Control estimates at least 300,000 Americans get diagnosed for Lyme each year, and the actual number could be 440,000, given that many small rural hospitals lack the staff and time to report Lyme cases.

And even though most people love seeing deer, that love can sour when people realize children get hit disproportionately by Lyme disease. According to CDC data from 2008 to 2018, kids 9 and under accounted for 25,594 (14%) of the nation’s 178,653 confirmed Lyme disease cases those years. The only group harder hit was 50- to 59-year-olds with 32,170 (18%) cases.

But hammering deer herds to reduce their numbers doesn’t always cut tick numbers, let alone curtail tick ailments. Adult deer ticks can sustain their numbers by attaching to other midsized mammals like dogs, foxes, coyotes, raccoons, or people. Deer numbers seem to have little impact either way on dog/wood tick populations.

Likewise, controlled springtime burns reliably reduce ticks by destroying their leaf litter habitats. Most burns, however, cover small areas and aren’t burned every year. As researchers at Old Dominion University in Virginia report, no control technologies succeed in all situations, and most have limited application.

Sprayed poisons often kill not only ticks but also honey bees, or they selectively kill ticks but require expensive annual applications. Still others involve bait boxes and tick tubes, which can be effective but logistically impossible if covering large areas. Perhaps the most intriguing effort involved a “tickbot,” a robot that drags a permethrin-treated cloth through the woods while attracting ticks with carbon dioxide. The ticks die when contacting the permethrin. Again, though, you’d need a large budget to field a tickbot army for treating large areas.

Absence of Evidence
Even so, tick-borne disease experts like Professor Sam Telford at Tufts Cummings School of Veterinary Medicine in Massachusetts argue that reducing deer numbers should be a “cornerstone of integrated tick management.” Telford also thinks it’s “unethical to wait for long-term methods to work and do nothing to prevent infection in the interim.”

He writes that most herd-reduction efforts aren’t sustained, and research to evaluate how smaller deer herds affect human health is difficult and expensive. For instance, the only proven way to reduce Lyme disease at community levels is the Lymerix vaccine. In the late 1990s it reduced incidence by 60% to 80% but cost over $25 million.

Therefore, because most herd reduction efforts don’t last long enough, no one can confidently conclude that lower deer densities won’t reduce tick-borne diseases. “Such a conclusion is based on absence of evidence, not evidence of absence of an effect,” Telford wrote. He also said such assumptions harm “future attempts to use deer reduction as part of an integrated tick-management system.”

Telford argues that we didn’t have tick-borne epidemics until three main factors coincided: reforestation, suburbanization, and dense deer herds. Of those three factors, society has only one option to disrupt disease cycles on community levels: lower deer densities in smaller, site-specific locations. “Deer reduction would be most effective as part of an integrated tick-management program that comprises short-term and long-term approaches,” he wrote.

Telford concedes that long-term control efforts, and research to monitor tick numbers and disease rates, would be expensive. But bigger research investments could be justified, given the costs of tick-borne ailments.

Lorraine Johnson, chief executive officer and “Lyme Policy Wonk” columnist for LymeDisease.org, recently reported the combined costs of early and late chronic Lyme disease to the U.S. economy ranges from $1.1 billion to $1.6 billion annually. But if you figure that some chronic cases last a decade and longer, Lyme’s annual toll could range from $26.1 billion to $76.6 billion. She based those totals on data from the CDC and Johns Hopkins University that analyzed medical costs, indirect medical costs, travel for treatment, and lost productivity.

Johnson wrote that too many patients still aren’t diagnosed and treated early enough when treatments are most effective. Failure rates when treating early and late Lyme cases remain high, ranging from 35% to 50%. In fact, 63% of early Lyme patients developed late/chronic symptoms such as joint pain, memory loss, debilitating fatigue, musculoskeletal symptoms; and pain, weakness, and numbness from nerve damage. Those patients incurred $3,800 in medical costs because of Lyme disease on average, and required 66% more healthcare visits and 89% more emergency room visits in one year.

Too Many Deer?
David Clausen, a retired Wisconsin veterinarian who served six years on the state’s policy-setting natural resources board, worries about the deer’s role in tick-borne diseases. Clausen is also a lifelong deer hunter, and thinks hunters should be shooting more deer in states with overabundant herds.

“I’m amazed how suburban my county in northwestern Wisconsin has become, which means more people living among deer,” Clausen said. “We’re all seeing more deer, we’re seeing more Lyme disease, and we’re seeing more tick-borne diseases like the Powassan virus, which ticks can pass to people in 15 minutes, not 36 to 48 hours like Lyme disease. And yet everyone seems afraid to say what’s so obvious: We have too damned many deer.”

Dr. Grant Woods, owner/creator of “Growing Deer-TV” and The Proving Grounds in southwestern Missouri, has twice battled Rocky Mountain spotted fever and tested positive for Lyme disease. He thinks tick-borne diseases warrant an aggressive national response that includes prescribed fires, chemical treatments, permethrin-treated clothes, and deer herd management. But he’s skeptical that society is ready to tackle these complex challenges.

“We’re all rightfully worried about chronic wasting disease, but ticks cause real problems that kill some people quickly and plague other people for life,” Woods said. “In the past you’d take antibiotics for 10 days and you’re fine, but now you’re seeing Powassan disease killing people in 10 days, and chronic Lyme and red-meat allergies causing prolonged agony. Even with all that, it seems society lacks the will to control these diseases.”

Woods, however, thinks deer probably get too much of the blame, given their visibility and wide distribution. “Yes, we should look at deer numbers, but we have to look deeper than that,” he said. “I’m not buying that deer are the No. 1 evil link to ticks. If we could census the poundage of deer and rodents on the landscape, we’d have more pounds of rodents than deer. Lots of birds, rodents, and bigger mammals make life possible for ticks.”

Seeking Solutions
Meanwhile, wildlife agencies and health departments keep seeking possible solutions. The U.S. Fish and Wildlife Service, for instance, is trying to eradicate cattle tick fever around the Laguna Atascosa National Wildlife Refuge in Texas. The F&WS’s multi-pronged effort includes prescribed fires; increased bag limits to reduce whitetail numbers; mandatory check-station inspections for ticks on hunter-killed deer; emergency hunts to reduce exotic animals like Nilgai, an Asian antelope; and mechanical feeders that dispense ivermectin-treated corn to deer.

Ivermectin appears to kill ticks and other parasites on deer more effectively than permethrin, and the F&WS now allows its use on corn bait for deer hunting on private lands in Texas. If ivermectin sounds familiar, it’s because some people have self-medicated with veterinary ivermectin to treat COVID-19 symptoms. The Food and Drug Administration advises people not to take any form of ivermectin unless it’s prescribed by licensed healthcare providers.

Tests show pigs and cattle take 21 and 28 days, respectively, to shed ivermectin residues from their systems. Research also shows it likely takes deer two to three weeks to shed ivermectin after eating food treated with the drug, but the Texas Parks and Wildlife Department recommends a February to July feeding period, and instructs hunters to cut off ivermectin-treated bait 60 days before hunting.

“We made that recommendation several years ago to the Texas Animal Health Commission, and they’ve been adhering to it, as has the U.S. Department of Agriculture,” said Mitch Lockwood, the TPWD’s big game program director.

“You’ll always have stumbling blocks when trying to treat wildlife diseases, especially when you must account for people ingesting what you put out there,” Woods said.

Elusive Links
But linking deer to tick-borne diseases seems too convenient for some scientists. A 2012 study led by Taal Levi, then at the University of California-Santa Cruz, found red fox numbers more reliably predict Lyme disease increases than do deer numbers. In fact, when Cruz analyzed wildlife data from the 1970s to early 2000s for the Northeast and Midwest, Lyme disease seldom correlated with deer abundance.

Cruz explained the fox connection this way: Coyote numbers increased nationwide in the late 1900s, and they killed and harassed red fox, reducing their numbers. Coyotes don’t prey heavily on small rodents, so mouse, shrew, vole, and chipmunk populations climbed. Rodents often carry Lyme disease and make ideal hosts for deer ticks during their nymph stage.

In fact, a 2008 study found 80% to 90% of Lyme-infected tick nymphs picked up the bacteria from shrews, Eastern chipmunks, and white-footed deer mice. The deer tick’s nymph stage is also when it usually spreads Lyme disease to people.

Cruz reports that landowner wildlife surveys from 1970 to 2000 by the Wisconsin Department of Natural Resources showed red fox declines and coyote increases statewide, trends that mirror hunting data. For instance, Wisconsin hunters killed about 25,000 red foxes in 1984, but less than 5,000 in 2009, an 80% decline. Meanwhile, the state’s coyote kill increased 660% from 6,847 to more than 52,000 those years. Cruz found similar predator hunting trends in Minnesota, Virginia, and Pennsylvania during those years.

A 2017 study in the Netherlands also reported decreased Lyme disease where red foxes and stone martens actively preyed on white-footed mice and other small rodents. The lead researcher, Tim Hofmeester, trapped hundreds of mice and voles, counted their tick loads, and tested the ticks for Lyme disease and two other diseases. Hofmeester found that tick nymphs in areas with active foxes and martens had 15% the infection rate of nymphs living where fox and martens were less active.

But Hofmeester said rodent numbers differed little in his study areas, suggesting the predators weren’t suppressing rodents. He thinks the lower infection rates mean rodents move less when predators are present, reducing their opportunities to carry nymphs near people.

Punching the Feather Bed
All these complexities suggest we’ll never shoot our way free of Lyme disease or other tick-borne ailments. Even straight-forward efforts to reduce disease by killing ticks directly usually prove futile.

Most who try fail, and soon sound like Franklin D. Roosevelt a century before when he struggled to change the U.S. Navy’s bureaucracy while serving as its assistant secretary. As he prepared the Navy for World War I, a frustrated Roosevelt declared: “To change anything in the Na-a-vy is like punching a feather bed. You punch it with your right and you punch it with your left until you are finally exhausted, and then you find the damn bed just as it was before you started punching.”

Feature image via Captured Creative.