Kelly Oggenfuss is walking into the woods. Leading her team of four young researchers through a thicket of slender oak trees, she doles out assignments by letters corresponding to a grid. As early morning light filters through the canopy, Oggenfuss and her colleagues pull on latex gloves then disperse to gather surveillance data.
For 20 years, this has been a post-dawn ritual for Oggenfuss, a senior research specialist at the Cary Institute of Ecosystem Studies in Millbrook, New York, a bucolic town in the state’s Hudson Valley region. Four times a week from April to November — traditionally the most active tick season in the Northeast — she leads a platoon of field researchers as they don white coveralls, drive a pair of old Chevy Tracker SUVs down an overgrown dirt road, and hike to a five-acre tract designated “Henry Control” on the grounds of the institute. Their mission is to seek out and study ticks in one of the most tick-infested areas in America.
Oggenfuss and the others work methodically across a grid of 242 spring-loaded box traps, checking for rodents lured overnight by whole-oat seeds. Sharing updates via walkie-talkie, the team gathers after a squirrel is found in one of the traps. The new researchers transfer the animal to a plastic mesh sleeve and take turns examining it. A similar process unfolds with chipmunks.
Most often, the traps capture mice, which Oggenfuss and her team carry with them, still in the trap, until the grid check is complete. Then the group convenes around a collapsible table. As one researcher records data (grid location, gender, tag number, etc.), the others apply tags to the mice and collect blood, urine, and stool samples. Finally, Oggenfuss and her team meticulously comb the mice with tweezers and blow on their fur, pushing it aside in search of ticks.
“Look there’s a nymph,” says Oggenfuss. “And I’ve got one, two, three larvae. Can you see them?” She pulls a patch of the mouse’s fur back to reveal a blacklegged tick no bigger than a poppy seed burrowed into its head. The larvae are barely perceptible.
A researcher named Agi holds up another mouse. “Look,” she announces. “That’s a larva on top of that nymph. We have a co-feeding situation here.” The theory is that their feeding sites are so close that pathogens move between them easily, Oggenfuss explains. The potential result is one tick sharing infectious material directly with another through the host mouse as if it were a straw, speeding the spread of disease. “That could have an effect on infection prevalence,” Oggenfuss adds. “It’s one of the things we’re studying.”
Since 1992, the Cary Institute has been compiling a record of tick ecology that they believe to be the longest continuous study of this kind in the U.S. and possibly the world. Mostly its researchers encounter the blacklegged, or deer, tick (Ixodes scapularis), but in recent years, they’ve also been seeing increasing numbers of lone star ticks (Amblyomma americanum), which are native to the American Southeast but now range from northern Mexico to Canada. Over the years, an alarming number of ticks in the surrounding area have been revealed to carry Borrelia burgdorferi, the bacteria that causes Lyme disease, while others have tested positive for the pathogens that cause other tick-borne illnesses, including the potentially fatal Powassan virus.
Because ticks acquire pathogens from hosts, understanding tick-borne diseases means understanding ticks’ so-called disease reservoir, especially mice. If the urban rat was the primary carrier of bubonic plague, the country mouse is it for Lyme disease. And just as the fleas that fed on infected rats spread the plague, ticks that feed on infected mice transmit Lyme.
On this early May morning, the team’s trap yield is relatively modest — four mice, two squirrels, and a chipmunk. “It’s early days still,” says Oggenfuss. In August, during the so-called larval peak, the researchers sometimes catch as many as 220 mice and can find 150 or even 200 tick larvae crawling on a single mouse. It can be an unnerving moment. “When the ticks are looking for a feeding site,” Oggenfuss says, “the mouse fur just seems to move on its own.”
The process for counting ticks not affixed to hosts is called a drag — the researchers pull a one-square-meter sheet of fabric along the ground for 30 meters then tally the number of ticks affixed to it. Oggenfuss holds the Cary Institute record for ticks collected in a single drag: 1,700. As horrifying as that haul was — and it would, by extrapolation, put the tick population on the Cary Institute’s 2,000-acre campus at 2 billion — Oggenfuss is quick to note it was exceptional, and tick density is irregular. Her more conservative calculations of average tick populations, based on drags done during the same time of year (August, the larval peak), are only reassuring by comparison: upward of 20,000 ticks per acre, more than 100,000 on the Henry Control grid, and more than 40 million on the Cary Institute grounds.
The scary thing is, that’s nothing. Experts say the worldwide tick population is exploding,triggering a dramatic spike in the incidence of Lyme disease and a rise in other tick-borne illnesses, some of which, like Powassan, are far more dangerous than Lyme.
First identified in 1975 in the leafy New England town of Old Lyme, Connecticut, Lyme disease has now reached what experts consider pandemic proportions. According to the Centers for Disease Control and Prevention (CDC), the number of confirmed cases of Lyme disease in the U.S. has more than doubled in the two decades leading up to 2017 (the most recent year for which final figures are available) and increased 17% from 2016 to 2017 alone. More than half the counties in the U.S. are considered high-risk areas for Lyme, according to the CDC, and in some areas, as many as six out of 10 ticks carry the infection.
“It’s been a relentless expansion since the 1980s,” says John Aucott, director of the Lyme Disease Clinical Research Center at Johns Hopkins University School of Medicine. “There may be down years and up years, but the trends are in place, and there’s no indication that they’re going to reverse.”
We now live in a frightening new normal: It’s estimated that 300,000 people contract Lyme every year in the U.S., with victims found not just in traditionally tick-heavy areas like upstate New York and Maine, but also in all 50 states and Washington, D.C. While most people are cured quickly with antibiotics, some go on to experience lingering symptoms characteristic of Lyme, like headaches, fatigue, and joint and muscle pain, for months or longer after they’ve been treated, a condition known as post-treatment Lyme disease syndrome (PTLDS). According to a recent study led by experts at the Brown University School of Public Health, the number of people in the U.S. with PTLDS was estimated to be 1.5 million in 2016 and is predicted to rise to nearly 2 million by 2020.
“There is little doubt that [Lyme disease] is pandemic. It calls for a huge national and concerted international effort to bring it under control.”
Tick populations now exist on every continent, even Antarctica, and Lyme disease can be found throughout most of Europe, where it ranks as the most common vector-borne disease, and beyond. “To me, there is little doubt that it is pandemic,” says Mary Beth Pfeiffer, author of Lyme: The First Epidemic of Climate Change. “It’s in China, Russia, Japan, Australia. It’s moving fast into Canada. It is all across the U.S. It calls for a huge national and concerted international effort to bring it under control.”
The incidence of other tick-borne illnesses is also sharply rising. According to the CDC, the occurrence of those diseases in the U.S. has nearly tripled since 2004 and increased more than 22% from 2016 to 2017. In addition to Lyme, ticks transmit a slew of pathogens, including those that cause babesiosis, ehrlichiosis, anaplasmosis, southern tick-associated rash illness, tick-borne relapsing fever, tularemia, Colorado tick fever, Q fever, Rocky Mountain spotted fever, and Powassan encephalitis. Most of the bacterial diseases are treatable if diagnosed early. Others, like Rocky Mountain spotted fever, are potentially fatal, particularly in children, if not treated quickly. Incidences of spotted fever rickettsiosis, which includes Rocky Mountain spotted fever, increased more than 12-fold from 2000 to 2017 (up from 495 to 6,248). And while more rare still, cases of Powassan virus, which can kill one in 10 people who are infected and for which there is no treatment, are rising as well. In 2008, only two cases were reported. In 2016, that number jumped to 22 and again in 2017 to 33.
“Ticks account for more diseases than all other biting insects and arthropods in the United States,” says Ben Beard, deputy director for the Division of Vector-Borne Diseases at the CDC. “It’s hard to know what the maximum or the ceiling might be. All we can say is that the number of cases is growing every year.”
Alarms are going off all over the globe. South Africa, where tick-bite fever (a form of rickettsias) is common, has seen an increase in incidences of Crimean-Congo hemorrhagic fever (CCHF), which is deadly in 30% to 40% of cases. The tick that carries CCHF, a native of sub-Saharan Africa and eastern Europe, has been found in Spain, Portugal, Germany, and the United Kingdom, where it is believed to have been brought from Africa by migratory birds. Bites from the lone star tick have been shown to cause alpha-gal syndrome, which manifests in rapid-onset allergies to meat, typically beef and pork, that can result in unexplained anaphylactic reactions. There is no treatment, other than eschewing the consumption of red meat.
In North America, news reports in Maine and southern Canada this spring featured a shocking number of sightings of what are called ghost moose — skeletal-looking, malnourished, denuded animals that have rubbed off their fur in response to tick irritation after hosting up to 75,000 feeding ticks through the winter. Many emerged anemic after being the source of so many blood meals, and a number of calves died after losing too much blood to ticks — a vampire-like end to life known as exsanguination.
If Lyme disease has reached pandemic proportions, why haven’t we heard more about it? Because, experts say, Lyme doesn’t strike fear into people’s hearts the way some other illnesses, like Ebola or Zika, do. People respond to dramatic pictures or dramatic mortality, says Aucott.
“It’s hard for them to have a perspective on the real impact of Lyme disease because it doesn’t cause visible changes. People with Lyme disease don’t look sick.”