Lyme Disease: Types, Causes, Symptoms, and Treatment

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What Is Lyme Disease?

Lyme disease is a bacterial infection transmitted to humans through the bite of an infected Ixodes tick, also known as the blacklegged tick in the U.S.^1,2 Lyme disease is the most common tickborne illness in the U.S. and Europe.³

In the U.S., Borrelia burgdorferi, a type of spirochete, or spiral-shaped bacteria, typically causes Lyme disease.^1,3,4 In rare cases, Borrelia mayonii bacteria can also cause the disease.¹

A classic sign of Lyme disease is a rash at the site of a tick bite, that can present as a bullseye shape. It is known as erythema migrans. Other common symptoms during early infection include headaches, fever, chills, swollen lymph nodes, muscle and joint aches, and fatigue.^1,3,5

Lyme disease gets its name from the town of Lyme, Connecticut, where researchers first reported the disease in 1975 after investigating a group of pediatric and adult arthritis cases.⁶

Prevalence of Lyme Disease

The annual number of cases of Lyme disease in the U.S. has trended upward since 2006, according to the Centers for Disease Control and Prevention (CDC). Changes in what constitutes a case of the disease, as well as the COVID-19 pandemic, created some variations in the trend.⁷

From 2010 through 2018, healthcare providers diagnosed and treated an estimated 476,000 people in the U.S. for Lyme disease, up from roughly 329,000 in the five years before.⁸ Even so, state and local health departments reported only 30,000-40,000 cases annually from 2010 through 2018, suggesting many cases went unrecorded.⁸ The CDC issued a revised case definition for Lyme Disease in 2022. Under this new classification, 62,551 new cases of Lyme disease were identified in the same year. From 2017 through 2019, the annual case average was about 37,000.⁹

Regions

In the U.S., most Lyme disease cases occur in the northeastern and upper midwestern regions. In addition to Washington, D.C., the country has 15 high-incidence states, defined as states with 10 or greater confirmed cases of Lyme disease per 100,000 people on average for three years in a row:^10,11

Connecticut
Delaware
Maine
Maryland
Massachusetts

Minnesota
New Hampshire
New Jersey
New York
Pennsylvania

Rhode Island
Vermont
Virginia
West Virginia
Wisconsin

Lyme disease is not limited to these areas. Between 2008 and 2015, states neighboring high-incidence states, for example, saw an increase in confirmed Lyme disease cases.¹⁰

Seasonality

Ticks typically bite in spring and summer, when people spend more time outside and in wooded and grassy areas.^7,12,13 However, tick activity varies based on geography, starting in some places as early as March and continuing in some places as late as December.¹⁴ Because ticks can be active whenever the temperature is above freezing, it’s still possible to contract Lyme disease during colder months.¹⁵

Who Is at Risk of Lyme Disease?

Although anyone can get Lyme disease, people who spend time outdoors in areas where the disease is endemic are at greater risk.¹⁶ Higher-risk groups may include outdoor hobbyists such as gardeners, hikers, campers, and hunters as well as outdoor workers such as farmers and landscapers.¹⁷

While Lyme disease can affect people of any age, the highest reported incidence of Lyme disease in the U.S. is in children aged 5-9 years old and adults aged 65-74.⁷ In 2022, people assigned male at birth accounted for a higher percentage of total Lyme disease cases (57.3%) than people assigned female at birth (42.7%).⁹

From 2008 to 2022 , among people assigned male at birth, children aged 5-9 had the highest percentage of cases (4.95%), followed by adults aged 55-59 (4.85%) and 60-64 (4.71%), and children and teens aged 10-14 (4.61%). Among people assigned female at birth, adults aged 55-59 saw the highest percentage of cases (3.91%), followed by adults aged 60-64 (3.82%).⁷ Lyme disease is most often reported in people who identify as white.⁷ Experts don’t know why, but it might be because the characteristic rash is more difficult to see on darker skin.¹⁸

Causes and Risk Factors

What Causes Lyme Disease?

In the U.S., the spiral-shaped bacteria (spirochete) Borrelia burgdorferi are typically responsible for Lyme disease diagnoses.^3,4Borrelia mayonii bacteria can also cause Lyme disease, with rare cases reported from the north-central part of the country.²

Lyme disease is a vector-borne disease. A vector is an organism—typically a bloodsucking insect—capable of transmitting infectious pathogens between humans or from animals to humans.¹⁹ Ticks carry the Borrelia burgdorferi or B. mayonii bacteria and transmit the spirochetes when they bite humans, causing the infection known as Lyme disease.¹

Ticks That Transmit Lyme Disease-causing Bacteria

In the U.S., two species of blacklegged ticks transmit the bacteria responsible for Lyme disease.² The blacklegged tick, or Ixodes scapularis, is common in the eastern and upper midwestern U.S. These regions report Lyme disease cases at higher rates than other regions of the country. The western blacklegged tick, or Ixodes pacificus, is responsible for infections in Pacific coast states like California, Washington, and Oregon.^2,20

Blacklegged ticks (Ixodes scapularis) are also referred to as deer ticks.² However, deer do not carry or spread Lyme disease.^2,21

How Ticks Transmit Lyme Disease-causing Bacteria

Blacklegged ticks typically crawl onto humans who have brushed against low-lying shrubs or vegetation where the tick was present.^22,23 The bacteria that causes Lyme disease is transmitted from the tick to the human when it bites. Research suggests that a tick must remain attached for approximately 36 hours or more to transmit the bacteria that causes Lyme disease.²²

This can happen during various stages of the tick’s life cycle, but ticks in the nymphal stage, which occurs between May and August, cause most cases of Lyme disease. This is also when people tend to spend more time outdoors. Furthermore, nymphal ticks are smaller than adult ticks, making them more difficult spot. In contrast, adult ticks, which are active in late summer and early fall—periods when people are also active outdoors—may be easier to detect due to their larger size.^22,23

The Tick Life Cycle
The life cycle of a blacklegged tick lasts two to three years and goes through four life stages: egg, larva, nymph, and adult.^2,23
After hatching, ticks must eat—often referred to as taking a blood meal—at each stage. Adult females also must consume blood to produce eggs.^2,23
Blacklegged ticks feed on various birds, amphibians, reptiles, and mammals, like rodents.^2,23 Deer are an especially important source of both blood and transportation for ticks, though deer do not pass on the bacteria that cause Lyme disease.²
Ticks in the larval and nymphal stages acquire the bacteria by feeding on infected animals, typically rodents. The bacteria remain within the tick as it transitions into its next life stage. Nymphal and adult ticks can then pass on the spirochetes during their next blood meal.²
Ticks in the nymphal stage are likely responsible for most Lyme disease cases.²² While adult ticks are typically the size of a sesame seed, nymphal ticks are tiny, roughly the size of a poppy seed, making them harder to detect.²
Transmitting Lyme Disease to Humans
Because they don’t fly or jump, ticks wait for new hosts on low-lying grass or shrubs before climbing onto them to feed. This behavior is known as “questing.”²³
Blacklegged ticks often attach and feed in moist, hairy, and hard-to-see spots on the body, such as the groin, armpits, or scalp.^12,24
In most cases, it takes 36-48 hours or more for a tick to transmit the bacteria that causes Lyme disease.^2,24 Therefore, if you remove a tick within 24 hours, you have a good chance of preventing Lyme disease.²⁴

Lyme Disease Risk Factors

While ticks can bite anyone, certain factors contribute to the overall risk of contracting Lyme disease. Outdoor recreation, time of year, and different terrain types can all make a person more or less likely to be bitten by a tick and develop the illness.¹²

Region
Most Lyme disease cases occur in the northeastern and upper midwestern regions of the U.S.²⁵
Habitat
Ticks typically live in environments that are shaded and moist. This includes wooded, brushy, leafy, and grassy areas.^22,24
Season
Most Lyme disease cases occur during the warmer months, particularly during May through August. This is the peak activity period for nymphal ticks.²² However, ticks can be active year-round if the temperature is above freezing and the ground is thawed.¹⁵
Lifestyle
In general, anyone who lives or spends time outdoors in Lyme disease endemic areas is at risk.^2,16 People who spend a lot of time doing outdoor activities such as camping, gardening, or hiking or who work outdoors in tick-friendly habitats are at a higher risk of contracting Lyme disease.^16,17
Pets in Lyme Disease-endemic Regions
Pets, such as cats or dogs, can bring ticks that carry Lyme disease-causing bacteria into the home. Once in the home, these unattached ticks can potentially attach themselves to humans or other pets.²⁶
Pets can get Lyme disease. However, there’s no evidence that they can pass it on to their owners or other pets.²
To avoid pets bringing ticks into the home, owners may consider treating their pets with reliable tick-prevention and control products. Dog owners may also ask their veterinarian about Lyme disease vaccinations for their animals. Before recommending vaccination, a vet may consider factors such as where you live, your dog’s lifestyle, and its overall health.²⁷
Travel
Traveling to an endemic region, specifically wooded areas of the northeastern and upper midwestern U.S., increases the risk of contracting Lyme disease.^10,25

Lyme Disease Prevention

Preventing Lyme disease requires a concerted effort of best practices and knowledge of where and when ticks are most active. Choosing proper clothing, using repellents, and having knowledge of tick habitats can all help prevent Lyme disease.^22,24,26

Habitats
Avoiding grassy, brushy, and wooded areas where ticks are likely to be present, especially in the warmer months, can help prevent Lyme disease. When spending time in these environments, people should take precautions such as avoiding touching leaf litter, soil, and vegetation and walking in the center of hiking trails.^22,24
Repellent
Treating clothing and outdoor gear with 0.5% permethrin may help protect against ticks. When applied to outdoor items, including clothing, boots, and camping gear, permethrin lasts for several washes. Pretreated clothes and gear are also available for purchase.²⁶
Insect repellents may help protect uncovered skin.^24,26 Repellents should contain DEET, picaridin, IR3535, Oil of Lemon Eucalyptus (OLE), 2-undecanone, or para-menthane-diol (PMD). To help people find the right skin-applied repellent, the U.S. Environmental Protect Agency hosts an online repellent search tool, which allows users to filter by factors such as active ingredient and protection duration.²⁶
Clothing
To reduce the risk of contracting Lyme disease, experts advise taking the following steps while spending time outdoors, especially in areas where ticks are likely present: Wearing a hat,²⁴ wearing long pants, long sleeves, and shoes that cover the entire foot to reduce exposed skin,^22,24 wearing light-colored clothing that has a tight weave so that ticks will be easier to spot,²² and keeping long hair covered, braided, or tied back.^22,24
Showering After Going Outdoors
Showering within two hours of being outdoors can reduce the odds of Lyme disease infection. Showering can wash off unattached ticks and provide an opportunity to check for ticks on the body.²⁶
Checking for Ticks
After being outdoors, people may consider using a full-length or handheld mirror to search their entire body for ticks. Experts recommend paying special attention to the ears, underarms, belly button, and back of the knees and areas in and around the hair, around the waist, and between the legs.²⁶
How to Remove Ticks Properly
In most cases, it takes 36-48 hours or more for a tick to transmit the bacteria that causes Lyme disease.² This means that if someone removes a tick within 36 hours, they have a good chance of preventing Lyme disease.²² The Centers for Disease Control and Prevention (CDC) recommends following these steps to remove attached ticks:²⁸
1. Using a pair of clean, fine-tipped tweezers, grab the tick as close to the skin as possible.
2. Pull upward steadily without twisting or jerking the tick, which can cause the tick to break apart, leaving its mouthparts stuck in the skin.
3. If the tick’s mouth breaks off, try to remove it with the tweezers. If that doesn’t work, leave it alone and allow the skin to heal.
4. Clean the area of the tick bite and wash hands with rubbing alcohol or soap and water.
5. Safely dispose of the tick by placing it in alcohol or in a sealed bag or container, wrapping it in a piece of tape, or flushing it down the toilet. Never attempt to kill a tick by crushing it between your fingers.
Experts warn against “household remedies” for tick removal, such as heat, petroleum jelly, and nail polish. They also suggest removing the tick immediately instead of waiting for it to “detach” itself.²⁸
For Dogs and Pets
To help prevent Lyme disease, pet owners may check their animals for ticks after trips outside, especially if they visited areas where ticks typically live.^24,27
To check a pet for ticks, the Food and Drug Administration (FDA) recommends examining the areas in and around the animal’s ears, eyelids, collar, and tail, along with under its front legs, between its back legs, and between its toes. If you find a tick, remove it promptly. For additional protection, consider treating pets with tick-prevention products.²⁴
There are also Lyme disease vaccination options available for dogs, as well as products that will prevent ticks from attaching to dogs and products that will kill ticks on dogs.^29,30
Avoiding Ticks Around the Yard and Home
Because ticks often live in grassy and brushy areas, the CDC recommends several tips to prevent Lyme disease:²⁶ Mowing the lawn and clearing tall grass, brush, weeds, or leaf litter at the edge of the lawn; placing a 3-foot barrier of gravel or woodchips between patio or play areas and wooded areas to inhibit tick migration; and placing play equipment, decks, patios, and other frequently used items in a sunny area away from trees, where ticks have a harder time surviving.^22,26

Lyme Disease Symptoms

Symptoms of untreated Lyme disease can vary widely depending on the stage of infection.³¹

Erythema Migrans
One of the most common and identifiable symptoms of untreated Lyme disease is a skin rash called erythema migrans, which occurs in 70-80% of cases.³¹
However, it does not always appear that way.²⁴ Erythema migrans rashes develop at the site of a tick bite after three to 30 days, appearing in about seven days on average. The rash is typically about 2 inches or greater in size and can grow as wide as 12 inches over several days.^20,31
The rash can occasionally be itchy or a little painful, can feel warm to the touch, and can appear anywhere on the body.³¹ Occasionally, some patients develop multiple erythema migrans rashes.³²
Lyme disease-related rashes may present in several ways and may look like other skin conditions. To help compare erythema migrans and similar skin conditions, the CDC hosts a page on Lyme disease rashes and lookalikes.³³
Tick bites often cause small red bumps at the site that can look like mosquito bites. This irritation is common, generally lasts for a day or two, and is not necessarily a sign of Lyme disease.³¹
Other Common Early Symptoms of Lyme Disease
Common early symptoms of untreated Lyme disease can include fever, chills, fatigue, muscle and joint aches, headache, and swollen lymph nodes, which may occur even without a rash.³¹
When left untreated, Lyme disease can spread to other parts of the body, including the heart, joints, and nervous system.^1,31 However, Lyme disease is almost never fatal.²⁴
Common Later Symptoms of Lyme Disease
Later signs and symptoms of Lyme disease may not appear for weeks to months.³¹
Once they appear, these symptoms can include erythema migrans rashes that appear on other parts of the body, dizziness, facial palsy, severe headaches, shooting pains in hands and feet, neck stiffness, arthritis and joint pain, irregular heartbeat, dizziness, and shortness of breath.³¹
Persistent Symptoms Following Treatment for Lyme Disease
Though the use of antibiotics can help resolve most Lyme disease cases in two to four weeks, some people experience lingering symptoms that can last for more than six months after infection.^34,35 These ongoing symptoms can include pain, fatigue, and trouble thinking.³⁴
The cause of these persistent symptoms is unknown. According to the Centers for Disease Control and Prevention and a study published in the journal Emerging Infectious Diseases in 2023, the bacteria that causes Lyme disease may trigger an autoimmune response like those that occur after other bacterial and viral infections.^34,35 It is likely that these persistent symptoms are linked to overactivation of the immune system, which includes the body reacting to parts of the dead bacteria that can sometimes remain after treatment, changes in metabolic activity, and too much inflammation.³⁵
There is currently no recommended treatment for people with persistent symptoms following recommended treatment for Lyme disease. While antibiotics can treat early localized and disseminated Lyme disease, prolonged use of antibiotics is ineffective and may come with serious, potentially deadly complications.³⁴

Stages of Lyme Disease

There are three stages of Lyme disease, each with its own set of symptoms.¹⁸

The early localized stage occurs in the first few days and weeks following infection.^18,31 In most cases, symptoms begin three to 30 days after the bite of an infected tick.³¹ Symptoms include:
- The development of an erythema migrans rash at the site of the tick bite.³⁶ The rash may be warm to the touch, and rarely may be itchy or painful.³¹
- Feeling generally unwell.¹⁸
- Symptoms mimicking the flu³⁷
- Fever.³¹
- Chills.³¹
- Fatigue.³¹
- Headache.³¹
- Muscle and joint aches.³¹
- Swollen lymph nodes.³¹
Up to 80% of people who contract Lyme disease will experience an erythema migrans rash.²⁴ Many people report symptoms only at the early localized stage of Lyme disease.¹⁸
Left untreated, patients may develop early disseminated Lyme disease. This stage typically occurs weeks to months after infection, potentially because of inflammation at many sites within the body.³⁶
The most common symptoms of this stage of Lyme disease include:³⁶
- Multiple erythema migrans rashes.³⁶
- Neurological abnormalities.³⁶
- Episodic headaches.³⁶
- Mild neck stiffness.³⁶
- Cranial neuropathy (particularly facial palsy).³⁶
- Motor or sensory radiculoneuritis.³⁶
- Certain diseases of the eyes.¹⁸
- Lymphocytic meningitis.¹⁸
- Heart conditions such as myocarditis, pericarditis, atrioventricular nodal block, and issues with how the heart beats.¹⁸
In the U.S., arthritis, typically in the knee, is the primary symptom of late disseminated disease.³⁶

Diagnosis and Treatment

To diagnose Lyme disease, the CDC recommends a two-step test, which checks blood for antibodies that the body makes in response to the infection. While both steps of the test are required, they use only a single blood sample. If the first blood test result is negative for Lyme, healthcare providers may forgo the second step.³⁸

If the first test is positive or indeterminate (also called “equivocal”), the CDC recommends laboratories run the second step. A Lyme disease diagnosis requires a positive or equivocal first step and a positive second step. In certain cases, the second test may be equivocal.³⁸

What to Know: Lyme Disease Testing

Because antibodies can take weeks to develop, recently infected patients may test negative for Lyme disease. Tests cannot accurately determine whether someone has been cured of Lyme disease because antibodies may remain in the blood for weeks or years after the infection goes away.³⁸

Other viral, bacterial, or autoimmune diseases may result in false positives. Therefore, healthcare providers may consider a patient’s likelihood of exposure to blacklegged ticks and other diseases that cause similar symptoms when assessing test results.³⁸

If symptoms suggest that Lyme disease is affecting the nervous system, a cerebrospinal fluid test (spinal tap) may be warranted. Symptoms that may suggest nervous system involvement include numbness in the feet or hands or neck stiffness. Healthcare professionals also may order a spinal tap if blood test results are inconclusive, or if they indicate the possible presence of Lyme disease.³⁹

Lyme Disease Treatment

Patients who receive treatment in the early stages typically recover quickly and fully. Early detection and appropriate treatment help prevent the late manifestations of Lyme disease.⁴⁰

Antibiotics

Healthcare providers often treat people with Lyme disease with antibiotics, such as:

Doxycycline, which is in a category of antibiotics called tetracyclines.^40,41,42
Amoxicillin, which is in a category of antibiotics called “penicillin-like antibiotics.”^40,41,43
Cefuroxime, which is in a category of antibiotics called cephalosporins.^40,41,44

The type of antibiotic and duration of treatment healthcare providers recommend may depend on which stage of Lyme disease the patient has. Healthcare providers may adjust the treatment plan based on factors such as age, medical history, allergies, pregnancy status, and underlying health conditions.^40,42

Global Impact of Lyme Disease

Lyme disease is not only a problem in the U.S. In fact, researchers estimate that more than 14% of the world’s population has had Lyme disease at some point.⁴⁵

Lyme Disease in Europe
Within Europe, Lyme disease occurs in as many as 22 countries. One study published in 2023 analyzed and compared the prevalence of Lyme disease antibodies among different European populations. In Western Europe, 13.6% of the population had antibodies; 11.1% of the population in Eastern Europe had antibodies; in the northern and southern portions of the continent, 4.2% and 3.9% of the population had Lyme disease antibodies, respectively.^46,47
European countries with the highest incidence of Lyme disease include Belgium, Finland, The Netherlands, and Switzerland.⁴⁶
Lyme Disease in Asia
In Asia, infected ticks have been found in western Russia, Mongolia, Japan, and northeastern China. The prevalence of human infection in these areas, though, is not as high.⁴⁸ Data from many of these regions is likely incomplete because of factors such as poor disease awareness and the lack of diagnostic capabilities. As a result, Lyme disease may be substantially underreported.⁴⁹
Climate Change
Some studies suggest that climate change may increase the risk and prevalence of Lyme disease as warmer temperatures may expand the range of ticks. For example, studies point to more cases of Lyme disease in areas of Canada previously uninhabitable for blacklegged ticks. This is potential evidence of climate change’s role in the areas where the disease is endemic.^49,50

Frequently Asked Questions About Lyme Disease

What is Lyme disease?
Lyme disease is a bacterial infection transmitted to humans through the bite of an infected Ixodes tick.^1,2 In Europe and the U.S., Lyme disease is the most common infection caused by ticks.³ It may cause symptoms such as a bullseye-shaped skin rash (erythema migrans), headaches, fever, chills, swollen lymph nodes, muscle and joint aches, and fatigue.^1,3,5
Is Lyme disease curable?
Yes, Lyme disease can typically be cured through the use of prescribed oral antibiotics for two to four weeks.³⁴ People with Lyme disease typically feel better quickly and fully when they receive early treatment. Early detection and treatment help prevent later manifestations of Lyme disease.⁴⁰ However, some patients may experience symptoms such as fatigue, pain, or trouble thinking for more than six months after treatment.^34,35
What are the symptoms of Lyme disease?
The most common early-stage signs and symptoms of Lyme disease are headache, fever, fatigue, and a bullseye-shaped rash known as erythema migrans.³¹
Is Lyme disease fatal?
It is uncommon for Lyme disease to be deadly. However, untreated Lyme disease can lead to persistent symptoms that may last months or years.²⁴
What does a Lyme disease rash look like?
The typical Lyme disease rash is called erythema migrans and occurs at the site of a tick bite. It is a circular rash that expands outward, often creating a bullseye or target-like appearance.³¹ However, the rash does not always appear that way.²⁴ It is typically approximately 2 inches or greater in size and can grow as wide as 12 inches over several days.^20,31
The rash may be itchy or a little painful, usually feels warm to the touch, and can appear anywhere on the body.³¹
How can I prevent Lyme disease?
The best ways to prevent Lyme disease are to avoid grassy, brushy, and wooded areas during the warmer months, and wear long sleeves and pants in areas where ticks are common. Certain repellents can deter ticks from biting and transmitting the bacteria that cause Lyme disease. For example, permethrin is effective when used to treat clothing and outdoor gear, as are repellents containing DEET.^22,24,26
When returning from outdoor activities, examine clothing and equipment for ticks. You should also check your pets if they accompanied you. Showering within 2 hours of outdoor activities is advised, as is scanning your body for ticks. They may gravitate towards the waist, beneath the arms, between legs, near the ears, in the hair, near or in the navel, or behind the knees.²⁶
What times of year do I have to worry about Lyme disease?
The incidence of Lyme disease is highest during the warmer months. In the U.S., that is May through August.^7,12 However, ticks carrying Lyme disease-causing bacteria may be present any time of year.¹⁵

References
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