Boy’s fever and rash after insect bite


The parents of a 4-year-old boy who lives in eastern Maryland near the Pennsylvania line are worried about an expanding rash on his back, which started as a small red bump a week ago following a summer picnic. The boy has had a low-grade fever and has not been acting like himself for a few days.

The case

The parents of a 4-year-old boy who lives in eastern Maryland near the Pennsylvania line are worried about an expanding rash on his back, which started as a small red bump a week ago following a summer picnic. The boy has had a low-grade fever and has not been acting like himself for a few days.

NEXT: What's the diagnosis?


Dermcase diagnosis: Erythema migrans, early manifestation of Lyme borreliosis


Lyme disease is the most common tick-borne illness in the Northern Hemisphere, most often found in the Northeast and upper Midwest regions of the United States.1 The incidence of Lyme disease is estimated to be roughly 107 per 100,000 person-years.2 It is caused by the spirochette Borrelia burgdorferi sensu lato genospecies.3 In Europe, Lyme borrelia is mainly caused by B afzelii,B garinii, and B burgdorferi sensu stricto. In the United States, Lyme is mainly caused by B burgdorferi sensu stricto and B mayonii, a recently identified B burgdorferi sensu lato genospecies associated with Lyme borreliosis in the upper Midwest. Transmission is via Ixode scapularis or Ixode pacificus ticks.3,4

Clinical manifestations

The 3 phases of Lyme borreliosis are early localized, early disseminated, and late disseminated. Erythema migrans (EM) is a characteristic finding of early Lyme borreliosis, typically manifesting 7 to 14 days after the tick bite and prior to development of an antibody response.5

Erythema migrans starts as a round or oval erythematous macule or papule that expands into an erythematous patch over the course of days or weeks. As it expands, it may develop a target or annular shape with central clearing.5 Central clearing may not appear in all EM lesions; it has been reported in 9% to 37% of cases in large studies of culture-positive EM.6 The lesions may have localized mild pruritus, tenderness, and rarely central vesicles (roughly 7%). The lesion can occur at the primary site of the tick bite or at secondary sites after B burgdorferi has spread.5 Systemic manifestations associated with EM include fatigue, fever, arthralgia, myalgia, and stiff neck.6

Of note, clinical manifestation of infection from the novel B mayonii may differ from B burgdorferi sensu stricto, with patients presenting with fever, nausea, vomiting, and a diffuse macular rash that is not characteristic of EM.3,6

Next: Boy's "mole" appears overnight

Clinical diagnosis of Lyme borreliosis based on EM and geographical collaboration is sufficient.1,4 Serological testing may be negative in the first few weeks of early Lyme borrelia.1,5 Lab findings of anemia, leukopenia, and thrombocytopenia are rare in Lyme borrelia and can suggest co-infection with human granulocytic anaplasmosis or babesiosis, or an alternative diagnosis.5,6

Differential diagnosis

Erythema migrans can be confused with other skin lesions associated with arthropod bites, tinea infection, and staphylococcal and streptococcal cellulitis.5 Reaction to an arthropod bite can be differentiated from EM by the rapid onset of rash from the bite, spontaneous resolution in a few days, and lack of systemic complaints. Tinea infection can also present with an erythematous border with central clearing but would also have irregular borders with scaling. Skin finding from staphylococcal and streptococcal cellulitis typically develop rapidly, evolve over hours (rather than days of EM), and are more frequently painful. Other considerations include fixed drug eruption and urticaria.


Management of Lyme borreliosis depends on the stage of the disease. For pediatric patients with EM associated with early disease without neurologic involvement or atrioventricular heart block, the current recommendation is amoxicillin 50 mg/kg/day divided into 3 doses (maximum 500 mg/dose); cefuroxime axetil 30 mg/kg/day divided into 2 doses (maximum 500 mg/dose); or doxycycline 4 mg/kg/day divided into 2 doses (maximum 100 mg/dose).4 Doxycycline is contraindicated in children aged younger than 8 years.

The patient

Within 24 hours of starting oral amoxicillin, the patient’s target-like red plaque began to fade and his symptoms resolved. His parents reported that they had removed a small tick from the center of the lesion the morning after the picnic.

The boy completed a 2-week course of antibiotic, and his parents noted that the rash had completely cleared within 3 days of starting treatment.




1. Moore A, Nelson C, Molins C, Mead P, Schriefer M. Current guidelines, common clinical pitfalls, and future directions for laboratory diagnosis of Lyme disease, United States. Emerg Infect Dis. 2016l;22(7):1169-1177. 

2. Nelson CA, Saha S, Kugeler KJ, et al. Incidence of clinician-diagnosed Lyme disease, United States, 2005-2010. Emerg Infect Dis. 2015;21(9):1625-1631.

3. Pritt BS, Mead PS, Johnson DK, et al. Identification of a novel pathogenic Borrelia species causing Lyme borreliosis with unusually high spirochaetaemia: a descriptive study. Lancet Infect Dis. February 5, 2016. Epub ahead of print.

4. Wormser GP, Dattwyler RJ, Shapiro ED, et al. The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2006;43(9):1089-1134.

5. Nadelman RB. Erythema migrans. Infect Dis Clin North Am. 2015;29(2):211-239.

6. Nadelman RB, Nowakowski J, Forseter G, et al. The clinical spectrum of early Lyme borreliosis in patients with culture-confirmed erythema migrans. Am J Med. 1996;100(5):502-508.

Ms Doong is a 4th-year medical student, Johns Hopkins University School of Medicine, Baltimore, Maryland. Dr Cohen, section editor for Dermcase, is professor of Pediatrics and Dermatology, Johns Hopkins University School of Medicine, Baltimore. The authors have nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article. Vignettes are based on real cases that have been modified to allow the authors to focus on key teaching points. Images also may be edited or substituted for teaching purposes.

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