A few months ago, the icy breath of the north that normally tucks itself over the Arctic during the winter blasted into the Northeast, prime tick country. This prompted climate scientists to look for links between a weakened polar vortex and a warming world. But those who study arachnids were interested in other signs … like fewer ticks.
In January, Thomas Mather, PhD, an entomologist known to many as the “tick guy,” trudged through thick snow in Kingston, R.I., looking for the spot where he’d buried vials of deer ticks the day before. The overnight temperature had fallen to a tick-numbing three degrees. Locating the vials, he sprinkled the tiny black specks on his palm. They sat there like pepper. Then they began to move.
For ticks, it seems, the ice age was a snowbird’s vacation. So don’t drop your guard, warns Mather, director of the University of Rhode Island’s Center for Vector-Borne Disease and its outreach arm, the TickEncounter Resource Center (TERC). Mather has spent two decades studying the rise of the blacklegged tick—commonly called the deer tick—in Rhode Island.
“I’m pretty certain that we won’t really be able to credit winter’s serial polar vortices for whatever the ticks are or are not doing in the spring,” he says. It’s not about the weather, but cycles. In their two-year lifespan, ticks feed on the blood of hosts during three growth stages: larval, nymphal and adult. According to Mather, the deer tick problems we’re facing in 2014 were largely decided last August and September by the number of larval ticks that found infected rodent hosts. “That will determine both the summer nymph populations and fall’s adult tick abundance,” Mather says.
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In recent years, those cycles have produced record numbers of nymphs at the sites his team sample each summer. So many, in fact, that he considers it a public health crisis in his state, which is part of the East Coast “tick-belt.”
Mather says that human and pet encounters with ticks are skyrocketing, and while ticks don’t always carry a disease, they may, and many of those diseases are dangerous.
Between 2006 and 2010, Veterinary Week reported a 30 percent increase in the rate of dogs exposed to tick-transmitted diseases. Among them: The aggressive lone star tick can transmit ehrlichiosis, one of the most common and dangerous tick-borne diseases in dogs. The brown dog tick and American dog tick also spread ehrlichiosis, babesiosis and Rocky Mountain spotted fever (RMSF).
Then there’s the deer tick. Although there are hundreds of species of ticks—all of which are relatives of spiders and mites, in the U.S. —the deer tick is number one on the most unwanted list. It spreads several dangerous infections, Mather says, and topping that list is Lyme disease.
Trail of Infection
The deer tick in the East and the related western blacklegged tick are the only known transmitters of Lyme disease in the United States. The trail of infection typically begins with rodents or, in the West, lizards, natural reservoirs of the Lyme bacterium, Borrelia burgdorferi. Ticks need a blood meal to reproduce, and acquire the bacterium when they bite an infected host. The next time they bite, they inject the bacterium into their unlucky meal source.
Where Lyme is found, so are deer, but the “deer tick,” as it’s commonly called, is actually the blacklegged tick, and it feeds on many different mammals, birds and reptiles. This tick has been on a tear in the Northeast, its range expanding, its pathogens mutating, ever since the disease it spreads—long known in Europe—was recognized in 1975 in Lyme, Conn.
Lyme disease was first diagnosed in a dog about 25 years ago, and now it’s one of the most common tick-borne diseases in dogs in the U.S., notes Cornell University’s Baker Institute for Animal Health. In several of the most affected states, one out of 15 dogs tested positive for Lyme disease in 2011, according to a study by the Centers for Disease Control and Prevention (CDC). And where dogs test positive, so do humans. In 2012, 95 percent of human cases were reported from 13 states concentrated in the Northeast and upper Midwest.
In parts of the Northeast, up to half of the deer ticks are infected with Lyme disease. In California, where Lyme also exists, the infection rate is far lower, with the disease mainly occurring in four northwestern counties.
A dog’s risk in such areas goes up and down. As noted on the Baker Institute’s website, even within highly infected regions, there are “hotspots of tick infestation and Lyme disease risk,” which “mingle with non-infested areas with much lower risk.” Even so, far fewer infected dogs than people develop the disease. Studies suggest that more than 75 percent of dogs in hyperendemic areas may be exposed to infected ticks, yet only about 5 percent develop Lyme. However, Lyme is only one of the diseases deer ticks spread to dogs; among the others are ehrlichiosis, babesiosis and anaplasmosis (“dog tick fever”).
There’s also a growing list of new diseases involving deer ticks, including one caused by the bacterium Borrelia miyamotoi, which mimics Lyme disease, and the rare but increasing Powassan virus and its variant, deer-tick virus. Powassan hasn’t been found in dogs, but dogs with neurological issues aren’t commonly tested for this rare disease, and such tests aren’t readily available.
In fact, even with available tests, diagnosing Lyme disease in dogs is challenging. Unlike viral diseases such as Powassan, Lyme is a bacterial infection and can be treated with antibiotics. But its symptoms, if any, mimic many other diseases. One common sign, lameness, takes two to five months to appear, according to the Baker Institute, and, unlike people, dogs don’t develop the telltale bull’s-eye rash around the bite.
A CDC study found that people in areas with a higher-than-average number of dogs with Lyme disease are at greater risk of getting it themselves. There’s no evidence that dogs spread it directly, but they may bring infected ticks into homes and yards.
And since dogs have a way of getting people outside, down that trail and—bag in hand—under that bush, it’s easy to see why the CDC says that dog owners face an elevated risk for Lyme disease.
Tick-Bite Protection and Prevention
Going outdoors is not the problem. What increases the risk of being infected is entering tick habitats. Especially if you go in thinking that ticks fall off trees. Or that they pounce, or fly. Surveys find that most people don’t know enough about ticks and their habits to ward them off.
“When it comes to tick-bite protection and disease prevention, we’ve learned that people tend to only focus on it after the fact,” Mather says.
That’s why TERC, which Mather heads, came into existence. Its goal is to entice people to learn more than they ever wanted to know about Ixodes scapularis (blacklegged or deer ticks)—ticks that carry the Lyme disease pathogen—and other species as well.
The idea for TERC began around 2004, when Mather decided to start “an aggressive, grassroots, tick-bite prevention program.” The tally wasn’t nearly as appalling back then, but by 2013, CDC estimates of the number of Americans diagnosed with Lyme disease each year hovered around 300,000, a whopping 10 times higher than anyone thought.
Although Mather felt that scientists already had solutions, “the link between science and people’s lived experiences with ticks was largely missing.” To fill this gap, his team took their fieldwork in a new direction: into tick-afflicted neighborhoods and to meetings with stakeholder groups. “People kept asking if we had a brochure or website,” he says. “After hearing that, oh, like 50 times, we started brainstorming.” They knew that brochures usually end up in the trash, but could a website reach people? “TickEncounter is what we came up with,” he says. It launched in 2006.
Today, the Internet teems with tick-related websites and information, and Mather believes it’s more important than ever to promote “a common core message” so the facts are clear to people. TickEncounter aspires to be the place people turn to for reliable and up-to-date information. The site isn’t soft on the facts; many people are susceptible, even likely to fall victim to tick-borne disease, which can be devastating. But simple preventive behaviors work. Before people can take action, Mather says, they need to believe in their own ability to successfully use those practices.
TERC’s unique graphic interface empowers users to snitch on the tiny army, ratting on its whereabouts and force-strength by season and region. The TickSpotters program, which includes crowd-sourced surveillance, recently added veterinary clinic reporting. Every two weeks, participating clinics send in patients’ ticks for identification. “These data are informing our ‘Current Tick Activity’ databases,” he says. Posts are updated every two weeks for nine U.S. regions. They plan to add an online dashboard with a map of results to show tick trends across America.
In February 2014, the TickSpotters page reflected the effects of the frigid weather, showing low tick activity in New England. Things were heating up on the West Coast, however, home to the western blacklegged tick. In fact, it’s always tick season somewhere, and people and pets can get Lyme disease even in winter.
“Pet owners seem most [affected] by adult ticks because they can see them,” Mather says, but the nymphs “are potentially more dangerous.” Nymph season is May through August, months during which people and dogs tend to spend the most time outside. Nymphs lurk in moist leaf litter in or near the edge of wooded areas. Because they’re so tiny at this stage, nymphs attach to small mammals near ground level, such as mice, which often carry Lyme. According to the Baker Institute, only repeated exposure to nymphs causes infection in dogs.
Adults, being larger, tend to bump into their hosts at higher altitudes. They wait aboard grasses and bushes, closest to animals’ largest body surface. They’re mainly a threat to dogs in fall and early spring. In winter, they only seek hosts when temperatures rise above freezing. Adults also transmit Lyme, babesiosis and anaplasmosis.
Despite the threats ticks pose, it’s not easy designing public education programs that work for everyone, health officials say. The problem is different for places in which ticks are entrenched and those with an emerging infestation. The bad news is, the number of the latter is definitely growing.
More Ticks, More Diseases
According to the U.S. Geological Survey, the temperate, humid, northeastern U.S. is a favorable place for ticks. More so all the time, it seems.
Ninety percent of canine Lyme cases now occur in the Northeast, according to the Companion Animal Parasite Council, whose website includes a “parasite prevalence” map by state, with confirmed canine cases by county. Lyme disease has also shown up in Northern California and on the Oregon coast, but there isn’t much evidence of spread.
The deer tick has even moved into Canada, where average temperatures have increased by 2.5º F over the past 60 years. One study suggests that tick-inhabitable regions in Eastern Canada will expand from 18 percent to more than 80 percent by 2020.
A 2013 study by researchers at the University of Toronto found that in the U.S., Lyme disease is shifting northward; the study noted large increases in 21 states between 1992 and 2007. This may be due “at least in part to the effects of climate change,” wrote the researchers. A Yale study also found links between Lyme disease outbreaks and milder weather in the Northeast. The 2004–2007 survey found the greatest risk in southern Maine through Washington, D.C., Minnesota and Wisconsin. Newer hotspots appeared to be cropping up in Illinois, Indiana, Michigan and North Dakota.
Warmer winters, which allow ticks to breed throughout the year, may be a factor, the researchers say. Warm, moist air may also extend their life cycle. They dismissed the Southeast as a location for Lyme disease, only acknowledging the lone star tick. But some say there’s growing evidence of a Lyme or Lyme-like infection there, too. In North Carolina, Lyme disease is up slightly, with a few cases diagnosed per year, but other diseases are being reported. RMSF cases rose 50 percent in 2012 compared to 2011. In June 2013, a child died from RMSF.
In 2009, the Ixodes affinis tick, native to South America and previously seen only in coastal Florida and Georgia, was found in North Carolina. Recently, the more southerly Gulf Coast tick, which transmits canine hepatozoonosis, was spotted there as well. This disease affects muscle cells and results in a debilitating and usually fatal condition. The aggressive lone star tick, historically found in southern and south-central states such as Texas and Florida, has been marching north and east for decades, scientists say. It has even worked its way into Maine and Ontario, Canada.
According to the CDC, cases of RMSF, mainly found in the Southeast, cropped up in an area of eastern Arizona where it had never before been seen—mostly in communities with many free-roaming dogs, who likely carried the brown dog tick. Newer deer tick pathogens are expanding their range, as well.
Many things are tipping the balance, scientists say, and they’re all wrapped together. They include the prevalence of deer, invasive plants, bird migration and traveling pets. Then there’s the sprawl of suburbs into woodlands, which exposes more people and pets to tick-borne diseases.
Some point to dwindling biodiversity, as animals that keep tick numbers down are increasingly shut out of their habitats by development and other human activities. Though ticks aren’t known to be any animal’s food source, opossums—rarely welcomed in the suburban landscape—groom themselves meticulously, and in the process, kill ticks by the thousands. As Rick Ostfeld, senior scientist at the Cary Institute of Ecosystem Studies, remarked, “Many ticks try to feed on opossums, and few survive the experience.”
Warmer weather and drought may be causing oaks to overproduce acorns some years, creating a boom in the white-footed mouse population. More acorns, more mice; more mice, more ticks. When the acorn crop crashes, fewer mice reproduce, and ticks are driven to seek fresh blood.
Some scientists think ticks migrate, following animal hosts that may be moving with the shift of plants.
And they may find perfect habitat in a dog’s backyard.
Tools to Stem the Tide
Farmers who take a sustainable approach often use a technique known as integrated pest management (IPM) to control pests and avoid toxic chemicals. Pet owners can learn from these farmers’ practices, which combine a range of methods and as few synthetic chemicals as possible. The U.S. Environmental Protection Agency’s website describes IPM as “an effective and environmentally sensitive approach” that can be applied in homes and gardens.
In fact, surveys find that homeowners in suburban neighborhoods in the Northeast are reluctant to spray chemicals to kill ticks. And at any rate, ticks are adapting to traditional pesticides. A recent CDC study found that spraying bifenthrin in a suburban area failed to reduce tick bites. Homeowners do widely accept methods such as brush and leaf-litter control or landscape barriers, which experts say offer medium levels of control.
TERC doesn’t rule out pesticides to control deer ticks, but suggests careful targeting to limit their use. Their recommended approach combines host-specific “Tick Tubes” and habitat-specific perimeter sprays. They also discuss many other ways to keep ticks in check, including their web-based TickEncounter Risk Calculator. By answering questions about their landscaping and other factors, people can use it to help determine the risks their yards offer, and can receive customized action plans.
At a 2013 EPA conference on tick-borne disease and IPM, Mather discussed his work, including the top protective actions people can take. Among them are knowing the ticks in your area and how to identify their life stages and seasonal patterns; taking protective actions, such as daily tick checks; and, of course, including pets in the plan. Even when a tick finds a dog, it has to be embedded for 24 to 48 hours to spread infection; quick removal drastically reduces the risk. TERC is also working on a vaccine for people, pets and wildlife.
So, the key to successful tick control lies in your own back yard, where about 75 percent of tick bites are said to occur. Seeing one tick is not enough to launch weapons. Signs of deer near your home, though, may be an important clue. To discourage ticks and their hosts, mow regularly, remove weeds and leaves, and make sure garbage and composting containers are rodent-proof. Prevention might also mean removing exotic vegetation or other welcoming habitat. Invasive bush honeysuckle and Japanese barberry, for example, attract white-tailed deer and mice (and thus, their ticks), a study found. Managing the growth of these plants significantly reduced the abundance of infected ticks. Paving or laying down gravel in heavily used areas also helps limit tick turf.
There is no one perfect solution to what seems to be nature's new normal. Come heat or hail, ticks are on the march. As summer unfolds, they’re sure to be out in force, seeking the most inviting habitats and hosts. Dog owners just have to think more like farmers … and tick guys.