By Gary M. White, MD

Erythema migrans

Erythema migrans (EM) is the skin manifestation of Lyme disease, a tick-borne infection caused by Borrelia bergdorferi.

Borrelia Mayonii

A new bacteria, Borrelia mayonii (Bm), has been identified as a cause of Lyme Disease [Lancet Infectious Disease 2016;Feb 5]. The clinical experience is similar, except that patients are more likely to present with nausea and vomiting as well as a diffuse rash instead of the typical "Bull's eye". This difference in presentation may mean that patients infected with Bm are not being considered to have Lyme borreliosis. Ixodes scapularis is still the likely primary vector to humans of Bm.


A red papule or macule which rapidly enlarges to form an annular lesion within a month of and at the site of a tick bite is characteristic of EM. Usually, the diameter is > 5 cm and the lesion is expanding. In contrast, a hypersensitivity reaction is usually seen while the tick is still attached or within 48 hours, is < 5 cm in diameter and not expanding. A small percent of patients may develop cardiac, neurologic or musculoskeletal changes. Typical symptoms of Lyme disease and their approximate incidence include fatigue 54%, headache 42%, myalgia 44%, arthralgia 44%, lymphadenopathy 23%, and fever 16%. Fever, headache, rash and neck pain are typically seen in the early (days) of the infection. Arthritis is experienced later (weeks after exposure).

When is Transmission More Likely?

Is it engorged?

When Should you Prophylax?

If all the following are met:

Single dose doxycycline: Adults: 400 mg, Children ≥ 8 yrs: 4 mg/kg (max 200 mg). If the patient codes not fit criteria, observe for symptoms.


The latest treatment recommendations should be consulted. In the past, adults and children 8 years or older may receive a 21 day supply of doxycycline 100 BID, amoxicillin 500 TID, or cefuroxime axetil 500 BID. For children < 8 years of age, amoxicillin 50mg/kg/day 3 divided doses or cefuroxime 30 mg/kg/day 2 divided doses.


Before you go

After returning home:

A vaccine is available which is administered in three separate doses (see A single dose of doxycycline 200 mg for patients who removed a tick within 72 hours that was attached, nymphal and at least partially engorged dramatically reduced the incidence of lyme disease.

Additional Pictures

Erythema migrans Erythema migrans Erythema migrans Tick on the skin


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