Not long ago, Lyme disease was considered both uncommon and easy to treat. People who suffered a tick bite and developed the disease’s hallmarks — an inflamed skin lesion, followed by fever, muscle aches, and fatigue — were treated with antibiotics and deemed cured. Complaints about lingering complications were largely disregarded or attributed to other non-Lyme causes.

Much has changed. As North America’s black-legged tick populations have increased, rates of the bacterial infections they transmit — Lyme disease and Rocky Mountain spotted fever, to name two — have likewise exploded. Over the past 13 years, the number of reported tick-borne diseases has roughly doubled in the United States, according to the Centers for Disease Control and Prevention(CDC).

Lyme disease is by far the most common tick-transmitted illness. And due to underreporting and diagnostic challenges, it’s possible that hundreds of thousands of people are now infected with Lyme each year. “The CDC’s number of reported cases is a gross underestimation of the total cases,” says A. Marm Kilpatrick, an assistant professor of infectious diseases and ecology at the University of California, Santa Cruz, who has studied the spread of Lyme disease. “We think there’s been a tenfold increase [in Lyme] over the last 20 years,” he says.

The medical community’s understanding of Lyme disease is still evolving.

As cases of Lyme disease have rapidly increased, the medical community’s understanding of the illness has likewise evolved. Richard Ostfeld, PhD, a distinguished senior scientist at the Carey Institute of Ecosystem Studies, says most Lyme disease researchers now accept that there are two stages of symptoms caused by the condition.

The early symptoms may include Lyme’s infamous bull’s-eye rash, although many people never develop a rash — or if they do, it doesn’t look like a bull’s-eye. “It could just be an enlarged red spot that is not particularly painful or itchy, but that is bigger than a quarter,” says Alan Barbour, MD, a professor of medicine and microbiology at University of California, Irvine, and author of the book Lyme Disease. Barbour says this rash is likely to develop within three weeks of a tick bite and can be treated with antibiotics. If left untreated, an infected person will usually develop flu-like symptoms — fever, fatigue, headaches, muscle pain — within a month. Again, treatment is a course of antibiotics.

If these early signs are missed or ignored, the flu-like symptoms usually subside, Barbour says. Even so, the Lyme infection is still present and, within a matter of weeks, can move to different parts of the body — causing a range of more serious and prolonged health issues. The infection can invade fluids around the joints, causing pain, swelling, and arthritis, often around the knee, Ostfeld explains. Or it can cause Bell’s palsy, a drooping on one side of the face.

Severe headaches, muscle weakness, and nerve pain are all possible complications, says John Halperin, MD, a neurologist with Atlantic Health System who has researched Lyme disease extensively. In rarer cases, heart irregularities or inflammation of the brain and spinal cord are also possible, Halperin says. By this stage of the disease — anywhere beyond a month or two after infection — Lyme disease is usually diagnosed via a blood test.

It’s at this point where Lyme disease starts to get controversial.

How Lyme disease is diagnosed is a concern. Ostfeld explains that most doctors in Lyme-riddled areas can diagnose the condition early based on a patient’s symptoms. But during the first month — when a rash and other symptoms emerge — there’s no test that can say for certain whether a person has Lyme. Even beyond a month, when blood antibody tests are available, experts disagree on their accuracy. Ostfeld says these tests are “okay” but can spit out false negatives and false positives. “They’re 20-year-old technology, and we need something better,” he says. Currently, the tests measure for antibodies, a signal that the body has fought the illness, rather than an active infection.

A subset of Lyme disease patients — roughly 5 to 10 percent, although no one’s quite sure — experience something known as “post-treatment Lyme disease syndrome,” or PTLDS, where they continue to experience symptoms after treatment. Those problems may include fatigue, headaches, pain, or muscle and joint problems.

This syndrome was once viewed as psychosomatic or, more commonly, as the result of unrelated health conditions ranging from multiple sclerosis to depression. While many still debate its legitimacy, PTLDS is now mostly accepted as a legitimate condition, Ostfeld and Barbour say. “The controversy that remains here,” Ostfeld says, “is whether the symptoms these people are feeling are the result of the Lyme infection having never cleared or of an autoimmune disorder stimulated by the infection.” He believes it’s the former, and some animal research supports this idea.

“There’s really no good approach to treating symptoms that persist for many years.”

Barbour feels differently. “I think for some people, the infection has turned the immune system on, and it stays on for a while even after you’ve taken care of infection,” he says. This may lead, Barbour adds, to people feeling “not right” or “cruddy” for a while, but these feelings are common after many types of infections and typically go away.

Asked about some of the longer-lasting, debilitating health issues many people describe as “chronic Lyme” — including everything from chronic fatigue and foggy thinking to gut issues and pain — Barbour says he’s skeptical that these symptoms are truly the result of Lyme disease. Halperin agrees. “I think a lot of people read things about Lyme, and then when they later develop nonspecific symptoms, they attribute them to Lyme when this is not the case,” he says.

These sorts of statements are frustrating for people who are truly unwell and have reason to believe Lyme disease is the cause. Doctors like Barbour and Halperin say they don’t doubt the legitimacy of these patients’ symptoms but disagree that Lyme disease is always the culprit. They argue that to slap a “chronic Lyme” diagnosis on people and, in some cases, to treat them with aggressive courses of antibiotics, denies them proper care for their health issues and potentially does them harm.

On the other hand, the medical community’s understanding of Lyme disease is still evolving, and people with symptoms of a chronic illness who believe it to be Lyme-related argue that some medical professionals aren’t taking their condition seriously. The NIH says increasing its research into Lyme disease and creating better treatments and diagnostics for both early and late-stage Lyme disease are among its priorities.

When it comes to treatment for both PTLDS patients and those who failed to receive care during Lyme’s early stages, there may not be an effective remedy. Barbour says antibiotic treatments can still work for patients who are diagnosed with Lyme even a year or more after developing symptoms. But if antibiotics don’t do the job, he says doctors today can really only treat the symptoms — prescribing anti-inflammatories for arthritis, say, or drugs for nerve pain — rather than offer a cure. “There’s no surgery or antibody therapy or anything like that for Lyme disease,” Barbour says.

In some cases, he says these people and PTLDS patients may resort to long-term courses of intravenous antibiotics. But case studies have shown that these treatments are usually ineffective and potentially even lethal. “There’s really no good approach to treating symptoms that persist for many years,” Kilpatrick adds.

For now, the only real defense against Lyme disease is an antibiotic course for those who are infected and increased awareness — among doctors and patients — of Lyme’s symptoms and measures to protect against tick bites.

“We know Lyme’s footprint is expanding a little bit every year,” says Fitzpatrick. And yet there is no comprehensive plan in place to stop it.