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Lyme, the tick-borne disease that’s spreading fast, explained

Summer is the season for Lyme. Here’s how to protect yourself.

Close Up Of An Adult Female And Nymph Tick Is Shown June 15 2001 On A Fingertip Ticks
In order for ticks to progress through their life stages, they need to feast on the blood of mammals. Here you can see an adult female (left) and a nymph tick.
Getty Images

If you’re spending time outdoors in America during the warmer months, there’s an increasing risk you’ll be infected with a disease spread by insects or ticks.

That’s the major finding of a recent report by researchers at the Centers for Disease Control and Prevention. When they looked at the number of illnesses spread by mosquitoes, ticks, and fleas between 2004 and 2016, they found that cases had more than tripled.

“It’s very important that the public is very aware that these are more than summertime nuisances,” said Lyle Petersen, an author on the report and the director of the CDC’s Division of Vector-Borne Diseases, last May. “You can get very severe diseases from ticks and mosquitoes.”

Out of the 642,000 total cases of mosquito-, tick-, and flea-borne illnesses tracked in the 13-year study period, 77 percent were from ticks. And of those, 82 percent were cases of Lyme disease, a debilitating and still mysterious illness.

Between 2004 and 2016, the researchers found, reported Lyme cases increased from 19,804 to 36,429. (But health officials think the real number of Lyme illnesses is closer to 300,000 every year.)

And one reason Lyme cases have crept up is that Lyme season has been getting longer, as the geography in which ticks can thrive and survive has expanded.

This at least partially due to climate change. “Temperature is very important,” Petersen told reporters. “If you increase the temperature, in general, tick populations can move farther north, expanding their range as well as increasing the length of tick season, which puts more people at risk for a longer period of time.”

Lyme disease typically peaks in May through July, when the ticks that carry the disease are most active. More than 90 percent of Lyme cases pop up in the Northeast, Upper Midwest, and mid-Atlantic. But the number of counties that are now deemed high-risk for Lyme has also increased by more than 320 percent since the late 1990s.

Here’s what you need to know about this growing threat.

1) Lyme disease spreads in humans when people get bitten by tiny vampires

Lyme is the most common vector-borne disease in the US, more common than West Nile or Zika virus. But unlike Zika, which is transmitted from mosquitoes to humans, the bacteria that causes Lyme, Borrelia burgdorferi, reaches people through tick bites after moving through a chain of other species.

B. burgdorferi typically live in mice, chipmunks, birds, and deer in wooded areas. And these are all animals that ticks feast on. The tick is in fact quite vampire-like — not an insect, but in the same family as the spider, mite, and scorpion — and progresses through its three life stages fueled by the blood of mammals.

That includes humans. They’re attracted to the warmth and carbon dioxide we give off. Though they can’t jump or fly, they typically crawl onto us (and other animals) when we brush against them — walking through tall grass, playing in fields. If the ticks are carrying Lyme or other pathogens, they can infect us when they bite. (The precise amount of time a tick needs to be attached to the skin to transmit Lyme isn’t known — though many claim it takes 24 to 36 hours. What is clear: The risk of infection increases the longer a tick is attached.)

Reported cases of Lyme disease in 2016.

According to the CDC, common Lyme symptoms include fever, headache, fatigue, and muscle and joint aches. There’s also that telltale skin rash, which manifests in a ring shape on the body — but not everybody who has Lyme gets a rash or even the bull’s-eye on their body. (Lyme-related rashes can also come in many shapes and sizes.)

A ring-like rash is sometimes an early sign of Lyme disease.

If Lyme is diagnosed early enough (within days to a couple of weeks), an antibiotic can treat the illness, said Richard Ostfeld, a Lyme disease researcher at the Cary Institute of Ecosystem Studies. But when it’s left untreated, the infection can spread into the joints, heart, and nervous system, causing more severe and dangerous symptoms like arthritis, heart palpitations, facial palsy, brain inflammation, and nerve pain.

In some patients, even those who have been treated for Lyme, symptoms can persist for months and researchers don’t fully understand why. More on “chronic Lyme” next — and why it’s still controversial.

2) Lyme can be difficult to diagnose, which has led to an ongoing controversy about “chronic Lyme disease”

Lyme can, in some cases, be really difficult to diagnose. Up to 30 percent of people never get a rash. Many can’t recall a tick bite. The blood tests approved by the Food and Drug Administration only look for Lyme antibodies — or evidence that a person’s immune system has fought off the disease.

This means that people who get the test too early may have a false negative because there aren’t enough antibodies in their system to show up in the test. People who get the test late may have a false positive, after their bodies have fought off the infection.

So doctors are often left to diagnose the disease on the basis of clinical symptoms that can be really vague.

“It’s very unfortunate we don’t have a good test for active infection,” said Brian Fallon, the director of the Lyme and Tick-Borne Diseases Research Center at Columbia University. “If we did, we wouldn’t have all these controversies about what to do with patients who have chronic Lyme symptoms.”

The main controversy he’s referring to stems from the fact that there are many patients who feel the medical establishment doesn’t recognize their lived experience with Lyme.

Again, Lyme symptoms can persist even after patients are treated with antibiotics. To address that, doctors came up with a medical diagnosis: post-treatment Lyme disease syndrome. It’s meant to describe patients who have well-documented prior Lyme infections, and who started antibiotics within six months of symptoms appearing, but still have lingering symptoms, including fatigue, pain, and joint and muscle aches.

“From a clinical perspective, [this definition] was not all that helpful,” Fallon explained. Some patients fell outside of it, “and felt the term was discounting persistent infection as the cause of their symptoms.”

These people — and some doctors and alternative medical practitioners — adhere to a different term that’s not accepted by the medical establishment: “chronic Lyme disease.” It’s made on the basis of clinical judgments and, often, unvalidated lab tests. It’s also sometimes applied to patients who haven’t even been in areas with Lyme disease.

“Although chronic Lyme disease clearly encompasses post-Lyme disease syndrome, it also includes a broad array of illnesses or symptom complexes for which there is no reproducible or convincing scientific evidence of any relationship to B. burgdorferi infection,” a critical review of chronic Lyme, published in 2007 in the New England Journal of Medicine, read. “Chronic Lyme disease is the latest in a series of syndromes that have been postulated in an attempt to attribute medically unexplained symptoms to particular infections,” the article concluded.

“It’s one of these diseases that has a very nonspecific, acute presentation,” said Duane Gubler, an infectious diseases specialist and former director of the CDC’s Division of Vector-Borne Diseases. “There are many people out there with symptoms of chronic fatigue and muscle pain, and Lyme disease has become one of the catchalls for people who have an illness of unknown etiology and there’s simply no clinical or lab test that can diagnose these people.”

3) It may not just be Lyme that’s infecting people

At the same time, there’s a lot we’re still learning about Lyme — and all the other infections ticks may simultaneously transmit to people. A third of all the known tick-borne pathogens were discovered in the past two decades, including:

  • Borrelia miyamotoi
  • Bourbon virus
  • Heartland virus
  • Rickettsia parkeri

So researchers and doctors have a lot to learn about how ticks can sicken people — and how the diseases they can spread interact with one another.

“We know new organisms are being discovered every one or two years ... in ticks,” said Fallon. “This is a time of continuous discovery in terms of what’s going on with tick-borne diseases.” So some of what we now think are symptoms of Lyme may be infections caused by other viruses and bacteria, or co-infections that may be interacting with the B. burgdorferi that causes Lyme.

Too few health care practitioners and patients are aware of that, wrote Richard Horowitz, a doctor specializing in internal medicine, at the New York Times:

The existence of these co-infections — so-called because they are often transmitted along with Lyme disease — explain why some people with Lyme remain chronically ill even after treatment. While the Lyme is identified and treated, these other infections are not. In addition, testing for co-infections is often unreliable, as it is for Lyme disease, so co-infections often go undiagnosed.

4) Lyme disease has become increasingly common. There are several reasons why.

Reported cases of Lyme disease by year, United States, 1995-2015.

In the US, the incidence of Lyme disease has doubled since 1991, from about four cases per 100,000 people to eight per 100,000 people. About 30,000 people are known to get sick with the disease each year, and the CDC thinks the real number of cases is about 10 times that because of underreporting. It’s also spread to a wider area of the country.

The risk for the disease is concentrated in the Northeast, mid-Atlantic, and Upper Midwest, with some pockets of Lyme cases on the West Coast.

Researchers have postulated several reasons why Lyme is becoming more common:

1) Changes in land use: One of the key drivers in the Northeast is the reforestation of areas that used to be farmland. The environmental features on farms reduce tick-borne disease risks in at least two ways, said Dustin Brisson, a University of Pennsylvania researcher studying Lyme.

“First, deer are important hosts for adult Ixodes scapularis ticks, and large deer populations are at least partially responsible for the large tick population sizes we see today,” he said. And farmers tend to shoot the deer when they go near crops. “Second, the absence of leaf litter on farmlands leaves ticks susceptible to dehydration and predation, which also reduces tick population sizes,” he added. Together, these factors help tick and deer populations thrive when farms are reforested — and increase the chances of spreading Lyme.

2) Hunting protections on deer: Hunting protections on deer have also helped the animals proliferate, and deer are particularly significant in spreading Lyme to new areas because adult ticks often feed and mate on them. (As Yale epidemiology researcher Katharine Walter said, “Deer help determine where ticks can survive and, therefore, the distribution of Lyme disease risk.”)

3) Suburbanization: With suburbanization, more and more people are living near animals that carry Lyme. “People have moved into these woodlots and built their houses right in the middle of where Lyme is maintained in the mouse and deer populations,” Gubler added. “That’s why we’ve seen such a dramatic increase in Lyme in the US.” These factors are helping Lyme’s geographic range spread, both northward and southward. “Each year, more and more people are in areas where they could potentially become infected,” Brisson said. And climate change certainly isn’t helping matters.

4) Global warming: The Environmental Protection Agency tracks the number of Lyme cases, along with heat-related deaths and severe weather events, as an indicator of global warming. That’s because researchers think climate change is another major driver of the trend — and they expect the situation to get much worse during the 21st century.

One of the most important determinants of whether ticks can survive is temperature, said Ostfeld. “Black-legged ticks need to feed on a host three times to survive and reproduce, and so they need ample time to find a host at each stage. If warm seasons are too short, many will likely drop dead before they happen to encounter a host, and the population will not persist.”

But global warming has extended the warm seasons around the planet.

"Tick survival depends on the local climate, and the distribution or geographic range of where ticks occur is increasing — and this is driven in part by climate change,” and, in particular, higher winter temperatures, Walter explained.

Warmer temperatures can also increase the developmental rate of ticks — the time it takes for an immature tick to fully develop. In one study, researchers estimated global warming increased tick reproduction by up to two times in the US and up to five times in Canada.

So climate change is aiding the disease twofold: helping ticks reproduce and helping them live in more parts of the US.

Gina Barton/Vox

5) More people know about Lyme: With more awareness among patients and doctors, more people may be looking for Lyme, so part of the increase we’re seeing may be an artifact of better detection.

4) There was a vaccine for Lyme, but it got killed by anti-vaxxers

We did have a vaccine to prevent Lyme disease, LYMErix, but it was removed from the market thanks to the anvi-vaccine movement.

The vaccine was approved in 1998, right around the time the discredited British physician was making fraudulent claims that the measles, mumps, rubella vaccine caused autism. As my colleague Brian Resnick reports, public fear about vaccines spread to LYMErix, including the idea that the vaccine lead to symptoms like arthritis. The media fanned these concerns, even though the FDA failed to find any data to actually suggest the vaccine was dangerous or caused autoimmune side effects. Even so, sales for LYMErix plummeted, and the vaccine maker pulled it from the market.

“Although studies never adequately substantiated the safety concerns associated with LYMErix,” the authors of a 2007 Epidemiology and Infection article wrote, “the decline in public tolerance for risk and uncertainty combined with the relatively low morbidity of Lyme disease contributed to the inability of the vaccine to find a market niche.” And as Resnick reported, the efforts to revive LYMErix have gone nowhere.

5) There is a right way to remove a tick


So, for now, the best way to prevent Lyme right now is to keep an eye out for ticks — and make sure you remove them correctly.

According to the CDC, you want to take a tweezer and get close to the skin, and then pull the tick upward. That’s because you want to make sure to remove the whole tick, without leaving any of its mouth parts — where bacteria may linger — in the skin.

After removing the tick, wash the bite area and your hands with rubbing alcohol or soap, and then take care to dispose of the tick by “submersing it in alcohol, placing it in a sealed bag/container, wrapping it tightly in tape, or flushing it down the toilet,” the CDC advises.

Here are a few other things the CDC recommends doing to avoid tick bites and Lyme:

  • When you’re spending time outdoors, especially in wooded areas, wear insect repellent and clothes that protect your skin.
  • Bathe after you’ve been outdoors, and check your body for ticks — including the back of your legs and your scalp.
  • If you’re worried ticks have embedded themselves in your clothes, throw them in your clothes dryer on high heat for 10 minutes.
  • Check your gear and pets for ticks (they can carry around the insects, which could attach to you later).
  • Walk in the center of trails, avoiding brushing up against tall grass.
  • Keep the space around your home clean and minimize the areas where ticks can lurk — cut your grass, pick up your leaves, and make sure there are no rodents around.

For more about Lyme Disease, tune in to the June 15, 2018 episode of Today Explained: Little summer vampires.