Lyme disease, or borreliosis, is a potentially life-threatening condition that is transmitted to humans by blacklegged ticks.

The tick infects the person with the bacterium Borrelia burgdorferi (B. burgdorferi).

At first, a rash may appear. This can disappear without treatment, but in time, the person may develop problems with the joints, the heart, and the nervous system.

Lyme disease is the most common tick-borne infectious disease in the United States (U.S.). The ticks pick up the bacteria when they bite mice or deer that are carrying it.

It was first reported in 1977 in a town called Old Lyme, CT.

The Centers for Disease Control and Prevention (CDC) registered 25,435 confirmed cases of Lyme disease and 9,616 probable cases in 2015, an incidence of 8.9 cases in every 100,000 people.

The highest number was in Pennsylvania, with 7,351 confirmed cases. New England, the mid-Atlantic States, and the upper Midwest are most prone to ticks that can spread Lyme disease.

Fast facts on Lyme disease

Here are some key points about Lyme disease. More detail is in the main article.

  • Lyme disease is the most common tick-borne disease in the U.S.
  • The disease can only be passed on through the bites of certain kinds of tick.
  • A common symptom of Lyme disease is an erythema migrans rash.
  • Without effective treatment, symptoms disappear, but more severe symptoms can emerge weeks, months, or years later.

Initial signs and symptoms of Lyme disease are usually very mild. Some people may not notice any symptoms, or they may think they have flu.

After the initial phase, further symptoms develop. Symptoms can disappear, but the disease can affect the body in other ways, years later.

Stage 1: Early Lyme disease

Erythema migrans (EM) is a rash that often appears in the early stage of Lyme disease, from 3 to 30 days after infection, or 7 days on average.

EM affects 70 to 80 percent of people who are infected.

The rash:

  • typically begins as a small red area that expands over several days, to reach a diameter of 12 inches or 30 centimeters
  • may lose its color in the center, giving a bull’s-eye appearance
  • usually starts at the site of the tick bite but can appear elsewhere as the bacteria spread
  • is not painful or itchy but may feel warm to the touch

The rash may be less evident on darker skin.

Stage 2: Early disseminated Lyme disease

The rash will disappear after about 4 weeks, even without treatment, but other symptoms can emerge days to months after being bitten.

These include:

  • meningitis, or inflammation of the brain and spinal cord, leading to headaches and a stiff neck
  • additional rashes
  • fever and chills
  • swollen lymph nodes
  • fatigue
  • pain in tendons, muscles, joints, and bones, especially in the large joints
  • heart palpitations or irregular heart beat
  • facial palsy, or loss of muscle tone in one or both sides of the face
  • dizziness and shortness of breath
  • nerve pain and shooting pains, numbness or tingling in the hands or feet

These symptoms may go away without treatment within a few weeks or months, but, in time, the person may experience further complications.

Anyone who may have Lyme disease should get medical help immediately. Early treatment is more effective.

Stage 3:Late disseminated Lyme disease

Also known as late Lyme disease, this may be the first sign of illness in some people.

Symptoms can emerge weeks, months, and even years after initial infection if a patient has not received treatment, or if antibiotic treatment has not been fully effective.

In some patients, this may be the first sign of illness.

It can involve problems with the nervous system and the heart.

The person may have:

  • difficulty concentrating
  • sleep and vision problems
  • memory loss
  • numbness, pain and tingling
  • irregular heart beat
  • joint pain
  • paralysis of the face muscles

Around 60 percent of untreated patients will experience recurrent bouts of arthritis with severe joint swelling, especially in the large joints.

Post-treatment Lyme Disease Syndrome

Even after treatment, a few people may experience post-treatment Lyme disease syndrome, sometimes referred to as chronic Lyme disease.

This involves nonspecific symptoms, such as fatigue and joint pain, that can persist for months after treatment.

Antibiotics are unlikely to help, so treatment aims to relieve symptoms, for example through rest and anti-inflammatory medications.

The symptoms should resolve in time.


In the U.S, B. burgdorferi, the Lyme disease-causing bacterium, enters humans through the bite of an infected blacklegged tick, either Ixodes scapularis or Ixodes pacificus.

The adult tick or the young nymph bores a tiny hole in the skin and inserts its mouthparts into the opening, attaching itself to the host.

Ticks tend to attach to hard-to-see areas of the human body, such as the scalp, armpits, and groin.

Generally, the tick must remain attached for at least 36 to 48 hours before transmitting the bacterium into a human.

As a result, the risk of getting Lyme disease from a tick, even where ticks are prevalent, is between 1.2 and 1.4 percent.

Most people get rid of the larger adults before they have time to transmit the bacterium, so human infections tend to occur as a result of bites from barely visible nymphs.

Is person-to-person transmission possible?

Lyme disease spread cannot spread between humans, for example by touching, kissing, or sexual contact.

Dogs and cats can get Lyme disease, but they cannot infect humans. There have been no documented cases of anyone contracting Lyme disease by eating venison.

Lyme disease cannot be passed on through the air, food, or water.

Lice, mosquitoes, fleas, or flies do not transmit it.

Pregnancy and breast-feeding

Some small studies have linked Lyme disease in pregnancy to birth defects or fetal death, but there has not been enough research to conclude that Lyme disease negatively affects pregnancy.

There are no reports of transmission through breast-feeding.

A woman who needs treatment for Lyme disease during pregnancy will receive a different kind of antibiotic treatment than usual.


Ideally, treatment should occur as soon as the EM rash appears.

If a person has been in an area where Lyme disease is common, and they have symptoms, treatment can start even without a blood test.

This is because the antibodies to the bacteria take from 2 to 6 weeks to show up in blood tests, so a blood test done within a month of infection may give a false result.

People should tell their doctor at once if they:

  • live in a high-risk area
  • have symptoms that could indicate Lyme disease
  • have recently been exposed to ticks

If early-stage Lyme disease is not treated, there is a serious risk of more severe symptoms later on, even years later.

Patients with swollen joints or neurological symptoms may be advised to have a PCR (polymerase chain reaction) test to check for bacterial DNA. Fluid is drawn from either the infected joint or the spine, in a spinal tap.


During the early stages of Lyme disease, treatment with antibiotic medication generally results in a rapid and complete recovery.

In the later stages, especially if the person has arthritis and neurological conditions, intravenous antibiotics, or antibiotic injections, will be necessary.

Even after treatment is over, patients may still test positive for anti-B. burgdorferi antibodies, but this does not necessarily mean they still have Lyme disease.


The incidence of Lyme disease appears to be on the rise in the U.S.

The National Science Foundation suggest this could be due to forest fragmentation, as smaller fragments of forest seem to harbor more ticks.

Small patches of woodland are common in cities and suburban and rural areas. They are a popular habitat for white-footed mice, because there are fewer predators.

White-footed mice are the main carriers of the bacteria that causes Lyme disease. When blacklegged ticks feed on the mice, they can pass on the bacteria.

The best way to prevent Lyme disease is to avoid tick bites.

Some ways to do this are:

  • be alert for symptoms
  • be aware of the risk, especially if living in or visiting New England, the upper Midwest or the mid-Atlantic states
  • use repellant on the skin, clothing, and hiking or camping gear
  • treat pets with anti-tick treatment
  • check your body, gear, clothes, and pets for ticks after spending time outdoors
  • shower after coming in from outside
  • dry clothes at a high temperature to kill ticks
  • ask pest control for advice about protecting your yard
  • discourage deer by fencing your yard
  • remove ticks quickly and correctly, and take a photo in case you need to show a doctor

When checking the body, the CDC suggest looking for ticks in the following places:

  • under the arms and behind the knees
  • in and around the ears
  • in the belly button
  • in head and body hair
  • between the legs
  • around the waist

If a tick is attached to the skin for less than 24 hours, it is unlikely to transmit Lyme disease.

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