A local and early form of Lyme disease, erythema migrans is a skin lesion appearing at the site of the bite of a tick infected with the Borrelia bacteria. Its appearance requires immediate consultation.

What is it ?

Erythema migrans is the most frequent clinical manifestation (60 to 90% of cases) and the most suggestive of Lyme disease in its localized early stage. As a reminder, Lyme disease or Lyme borreliosis is an infectious and non-contagious disease transmitted by ticks infected with the bacteria. Borrelia burgdorferi sensu lata.

How to recognize erythema migrans?

When it appears, 3 to 30 days after the bite, erythema migrans takes the form of a maculopapular lesion (small superficial skin spots forming small bumps on the skin) and erythematous (red) around the tick bite. This plaque does not cause pain or itching.

The lesion then gradually spreads around the bite, forming a characteristic red ring. After a few days or weeks, the erythema migrans can reach up to several tens of centimeters in diameter.

Rarer form, multiple localization erythema migrans appears at a distance from the tick bite and is sometimes accompanied by fever, headache, fatigue.

Risk factors

Any activity in the countryside, especially forests and meadows, during the tick activity period, from April to November, exposes you to bites from ticks potentially carrying the bacteria that cause Lyme disease. However, there is a great regional disparity in France. The East and the Center are in fact much more affected than the other regions.

Erythema migrans appears after being bitten by a tick carrying the bacteria Borrelia burgdorferi sensu loto. The tick can bite at any stage of its development (larva, pupa, adult). 

This typical clinical manifestation is usually sufficient for the diagnosis of Lyme disease in its early stage. In case of doubt, a culture and / or a PCR on a skin biopsy can be carried out to demonstrate the bacteria.

Without antibiotic treatment in the erythema migrans stage, Lyme disease may progress to the so-called early disseminated stage. This manifests itself in the form of multiple erythema migrans or neurological manifestations (meningoradiculitis, facial paralysis, isolated meningitis, acute myelitis), or even or more rarely articular, cutaneous (borrelian lymphocytoma), cardiac or ophthalmological manifestations.

Erythema migrans requires antibiotic therapy (doxycycline or amoxicillin or azithromycin) in order to eradicate the bacteria Borrelia burgdorferi sensu loto, and thus avoid progression to disseminated and then chronic forms. 

Unlike tick-borne encephalitis, there is no vaccine against Lyme disease.

Prevention is therefore based on these different actions:

• wear covering clothing, possibly impregnated with repellents, during outdoor activities;
• after exposure in a risk area, carefully inspect the entire body with particular attention to areas with thin and inconspicuous skin (skin folds behind the knees, armpits, genital areas, navel, scalp, neck, back of the ears). Repeat the inspection the next day: sip of blood, the tick will then be more visible.
• if a tick is present, remove it as quickly as possible using a tick puller (in pharmacies) taking care to respect these few precautions: take the tick as close to the skin as possible, pull it gently by rotating it , then check that the head has been removed. Disinfect the site of the tick bite.
• after removal of the tick, monitor the bite area for 4 weeks, and consult for the slightest skin sign.