Lyme disease, or Lyme borreliosis, is an infectious disease transmitted to man through the bite of a tick infected with the bacterium Borrelia burgdorferi.

The symptoms vary from one person to another

After a tick bite the risk of developing Lyme disease is about 1% to 2%.

If Lyme disease does develop its appearance can be marked by different manifestations affecting the skin, the joints or the nervous system.

Symptoms vary from person to person and can occur after different lengths of time.

Early signs

The most frequent early manifestation (in 60% to 80% of cases) is an erythema migrans, which appears 2 to 30 days after the tick bite.

It consists of a circular rash on the skin which expands gradually on the site of the bite, often with a central sparing.

Erythema migrans is not painful and resolves spontaneously after some weeks. It can also go unnoticed.

Erythema migrans should be distinguished from the local and temporary redness which can appear immediately after the bite.

Erythema migrans is a characteristic symptom of Lyme disease: its presence is sufficient in itself to make the diagnosis and start antibiotic treatment to prevent the development of the disease.   

The rash may be associated with ’’Flu-like symptoms” such as moderate fever, fatigue, muscular pain and headache.

Later manifestations

Other signs may appear months, even years, after a bite, even in the absence of previous erythema migrans.

If the infection is not treated, the bacteria can spread through the body and affect different organs: skin, joints, nervous system, heart etc.

According to the organ affected, the following symptoms (among others) may be observed:

  • multiple erythema migrans 
  • arthritis (inflammation of a joint)
  • neurological disorders
    • radiculitis (painful inflammation of nerve roots)
    • meningitis (inflammation of the cerebral membranes)
    • encephalitis (inflammation of the brain).
  • heart rhythm disorders (arrhythmia).

Post-Lyme syndrome

Some patients adequately treated for Lyme disease suffer from non-specific symptoms (fatigue, joint and muscle pain, concentration disorders, headache) which are described as a “post-Lyme syndrome”. The exact cause of this syndrome remains unknown.

Chronic Lyme disease

The expression “chronic Lyme disease” is sometimes used to describe non-specific symptoms (fatigue and pains) presented by some patients who also have antibodies against the Borrelia burgdorferi bacteria in their blood.

However, the presence of antibodies in the absence of typical symptoms for Lyme disease does not indicate that there is an active infection.

Indeed, antibodies can persist for several years after contact with an infected tick, without development of the disease.

The expression “chronic Lyme disease”, as it is badly defined, should not be used, since at present there is no evidence that these non-specific symptoms result of an infection by the bacteria in the past. 

4 reasons for not being alarmed

  • Not every bite is infectious (in Belgium only about 10% of ticks are infected).
  • An infected tick does not necessarily transmit the bacteria.
  • An infected person does not necessarily develop the disease.
  • Lyme disease can be treated effectively with antibiotics if it is diagnosed in time.


Sciensano ensures epidemiological surveillance of Lyme disease through a monitoring network of laboratories and general practitionersand a National Reference Centre  for Borrelia burgdorferi. 

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