Objective: To differentiate cases of physician-diagnosed erythema migrans and erythema migrans-like rashes associated with Lone Star tick (Amblyomma americanum) bites.
Design: Retrospective case series.
Setting: Private primary care clinic in rural Missouri.
Patients: Seventeen patients with physician-diagnosed erythema migrans following a definite Lone Star tick bite at the rash site.
Interventions: A biopsy was performed on all rash sites. All patients were treated with oral antibiotics.
Main outcome measures: Rash appearance, size, body location, multiple lesions, incubation times, associated symptoms, seasonal occurrence, histopathological features, tick stage and sex, patient age and sex, treatment response, growth in BSK II culture media, and serologic evaluation.
Results: Rashes associated with Lone Star ticks were similar to erythema migrans vectored by other Ixodes ticks. Differences were noted in Lyme disease serology results, especially flagellin-based enzyme immunoassays, and failure to yield spirochetes in BSK II cultures. Lyme serology results were often negative, but were also frequently inconsistent with results of controls without Lyme disease.
Conclusions: Lone Star ticks are associated with rashes that are similar, if not identical, to erythema migrans associated with borrelial infection. The recent isolation and cultivation of Borrelia burgdorferi from ticks (including 1 Lone Star tick) from the farm of a patient included in this report has raised the possibility that Lone Star ticks are "bridge vectors" for human borrelial infection. Although further investigation is needed, these rashes may be secondary to spirochetal infection.