A tick on clothing for an article on Lyme disease

Lyme disease is the most common bug-borne disease in the U.S., by far. Although the Centers for Disease Control and Prevention receives official reports of about 30,000 cases of Lyme every year from state health departments, the actual number of people being diagnosed and treated is nearly 15 times more. A recent CDC study estimated that the true yearly number of cases of Lyme over the last decade was likely closer to 476,000.

Given how common the disease is, you’d think that doctors and scientists would agree on the basics, such as the best ways to diagnose and treat it, and whether it can turn into a chronic condition.

But it turns out that when it comes to Lyme, there are still a lot of unknowns and plenty of debate.

“There is definitely some confusion and also some misinformation out there,” says Amy Schwartz, an epidemiologist at the CDC. “And it’s important to correct that, because without proper treatment, the condition can be devastating.”

Here’s a breakdown of what scientists do and don’t know about this dangerous and increasingly common illness.

How Lyme Disease Spreads

Lyme disease is spread primarily by bacteria known as Borrelia burgdorferi, which is transmitted to humans, household pets, and forest critters (including mice and deer) by the blacklegged tick, sometimes referred to as the deer tick, and the Western blacklegged tick. Rarely, Lyme can also be caused by newly discovered bacteria, Borrelia mayonii, also transmitted by blacklegged ticks. The CDC and the Infectious Disease Society of America (IDSA) agree that the tick has to remain attached for 24 to 48 hours in order to transmit Lyme-causing bacteria. (Other diseases spread by these ticks, such as the Powassan virus, can be transmitted more quickly.)

The disease is most common in late spring and summer, when young (poppy-seed-size) ticks are active and when people tend to spend more time outdoors.

Both the blacklegged tick and the diseases it carries are most common in the Northeast, Middle Atlantic, and North Central U.S. About 95 percent of people who get sick live in the District of Columbia and 15 states: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, West Virginia, and Wisconsin. While the tick population used to be limited to certain areas in those states, over the past two decades it has become more widespread, according to CDC scientists. 

Despite what you might read online, a vast majority of scientists agree that getting bitten by a blacklegged tick is essentially the only way to contract Lyme disease. You can’t catch it from sex, from eating deer meat, or from any other type of tick. You also can’t catch it directly from pets or other animals; only ticks can transmit the disease to humans. In rare cases, the CDC says Lyme can be transmitted to a fetus in utero from an infected pregnant person. 

How to Protect Yourself

The good news is that you can take several steps to reduce your risk of being bitten by an infected tick in the first place. Here's how:  

  • If you can, avoid areas with ticks, particularly during peak tick season (late spring to early fall). These include wooded and brushy areas with high grasses and leaf litter.

  • When spending time in a tick-infested area, dress carefully. Wear long sleeves, long pants, and long socks. Light colors are best because you can spot ticks more easily. To be extra safe, tuck your pants into your socks and your shirt into your pants.

  • Apply an effective insect repellent to your clothes and exposed skin. You can also try clothing treated with the insecticide permethrin, but don’t spray this chemical on your skin.

  • After being outdoors, take a shower to wash off any ticks that may be crawling on your skin but not yet attached. While you’re there, check your body for attached ticks, especially in skin folds such as in the armpits, groin, and behind the ears. Remember that young ticks are tiny—about the size of a poppy seed—so they can be difficult to spot. (See these tips for removing any ticks you do find.)  

  • Another useful measure: Pop your clothes in the dryer for 15 minutes on high to kill any ticks that may be hiding. 

How to Tell If You've Been Infected

The most obvious way to tell if you’ve been infected with Lyme disease is to check for the telltale bull’s-eye rash (called erythema migrans), which develops in 70 to 80 percent of cases. If you know you’ve been bitten by a blacklegged tick, you’ll want to keep a close eye out for this rash around the site of the bite.

If no such rash emerges—or if you never even found a tick on your body—but you develop symptoms of Lyme disease (fever, chills, joint pain) after being in a tick-infected area during tick season, you should ask your doctor to do a blood test.

That test has two tiers (or components) to it, and it’s important to make sure your doctor does both. “It’s a common misconception among doctors that you can skip the first part,” says IDSA's president, Paul Auwaerter, MD. “A lot of doctors do that, and they end up misinterpreting the results and misdiagnosing people.”

The timing of the tests is also important, he says. It can take weeks for the body to mount an immune response to Lyme-causing bacteria and to produce the antibodies that the blood tests are designed to measure. So if you test negative in the first month after being bitten (or after symptoms emerge), you may want to get retested a few weeks later. “The test really can’t pick up infection reliably in the first few weeks,” Auwaerter says. “But if people have had symptoms for longer than that, it’s highly accurate.”

When to Seek Treatment

If you test positive for Lyme (or if you have a tick bite plus the telltale rash), your doctor will most likely prescribe the antibiotic doxycycline. A one- to four-week course of the drug (depending on how you respond) will almost always wipe out the infection.

But you don't necessarily have to wait for symptoms or a blood test to get treated for possible Lyme infection. According to the CDC and IDSA, a single dose of doxycycline taken within 72 hours of a tick bite can prevent the disease from emerging altogether. This preventative treatment is recommended only if you received your tick bite in an area where Lyme is common. Your doctor must also be able to identify the tick that bit you as a blacklegged tick and be able to tell from how large it has swelled that it’s been attached to you for at least 36 hours.

That drug does cause side effects. It can make your skin more sensitive to sunlight, and it causes nausea or vomiting in about 20 percent of people taking it.

Some doctors may prescribe a different antibiotic, such as amoxicillin. But that approach hasn't been scientifically tested, and it’s unclear if or how well it works to combat Lyme.

What Is Chronic Lyme?

According to the CDC and IDSA, most people who test positive for Lyme respond well to antibiotics, even if they aren't diagnosed or treated until months or years after the initial infection. But some patients continue to suffer long after the standard antibiotic course.

Researchers have some ideas about the causes of this more difficult condition. It’s possible that the bacteria or some of the toxins they produce are sometimes able to survive the treatment. It’s also possible that the body suffers some sort of autoimmune response to the bacteria or the treatment itself. Or it could be that these illnesses are the result of multiple simultaneous infections—not just with Borrelia burgdorferi but with several other pathogens that the blacklegged tick is known to transmit.

But ultimately, doctors are divided over several basic questions: How common is this condition? Can it be treated with antibiotics? And what should it be called?

The CDC and IDSA refer to this as post-treatment-Lyme-disease syndrome, a condition for which no proven cause or treatment options exist. According to both, there's no evidence that prolonged antibiotic therapy works against Lyme disease.

But other groups, including the International Lyme and Associated Diseases Society (ILADS), call it chronic Lyme disease. They say it may stem from a failure to diagnose Lyme disease early on (often because the telltale rash doesn't emerge, and the person isn't aware of being bitten by a tick). They also say that long-term antibiotic therapy can work, though they say relapses are common and the road to recovery is bumpy.

Most doctors still reject the term chronic Lyme, in part because many people who say they have this condition haven't been infected with Borrelia bacteria. “We don’t use the term chronic Lyme because it can be confusing,” says Schwartz of the CDC. “Sometimes it is used to describe people who have tested positive for Borrelia and who have clearly had Lyme disease. But sometimes it refers to people with no such history.”

One thing everyone agrees on is that it will take time and much more research to sort out the mystery. And now some experts hope that research may be forthcoming because of the growing number of people experiencing another long-term post-infectious syndrome following infection with COVID-19, or “long COVID.”

Some researchers have drawn comparisons between long COVID and post-treatment Lyme because of their diverse array of symptoms, such as fatigue, brain fog, joint and muscle pain—complaints that can “appear vague, difficult to explain, multifactorial, or unexpected” and that can lead doctors to dismiss or minimize patients’ concerns, according to John Aucott, MD, director of the Johns Hopkins Lyme Disease Clinical Research Center, writing in The Lancet. He says that post-infectious syndromes of any kind “present the opportunity for novel, scientifically rigorous, inclusive, open-minded research with the aim of helping patients with these poorly understood conditions recover their health.”


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