Southern Tick–Associated Rash Illness

In early summer, an 8-year-old boy from rural central Virginia was brought for evaluation of a rash on his buttock (A). He had noticed the rash that morning, when it became pruritic. The father had removed a tick from the area about 10 days earlier. The child denied fever, headache, vomiting, fatigue, arthralgia, myalgia, and other symptoms.

Vital signs were stable. There was no lymphadenopathy. The 4 x 2-cm lesion had 2 central papules with an outer ring in a figure-eight pattern, consistent with 2 bites and 2 primary lesions. No other rashes were present. The skin lesion appeared to be consistent with erythema migrans. Early localized Lyme disease was diagnosed, and oral amoxicillin was prescribed. However, further review of the history revealed that the removed tick had a white spot on its dorsum, which is characteristic of Amblyomma americanum (Lone Star tick)(B).

Most experts do not consider the Lone Star tick to be a vector for Borrelia burgdorferi, the spirochete responsible for Lyme disease. However, the Lone Star tick has been implicated as a cause of southern tick–associated rash illness (STARI), also called Lyme-like illness, southern Lyme disease, or Masters disease.^1-3 The causative agent of STARI remains unclear. A spirochete (Borrelia lonestari) has been cultured from Lone Star ticks and from the lesion of one patient with STARI; however, attempts to identify this organism in other patients with STARI have been unsuccessful.

STARI presents similarly to Lyme disease, with a target-like rash that develops around the site of a tick bite. The lesion typically appears within 7 to 10 days of the bite and expands to a diameter of 3 inches or more. Patients with STARI may present with fever, headache, fatigue, and muscle and joint pains, although they tend to be less symptomatic and recover more quickly than patients with Lyme disease. Differentiation of STARI from Lyme disease on the basis of early clinical signs alone is unreliable. Fortunately, STARI is not associated with the later, serious complications-arthritis, carditis, neurological symptoms-that are sometimes seen in Lyme disease.

Biopsy of the lesion is not generally indicated. However, with hematoxylin-eosin staining, STARI lesions show a principally lymphocytic infiltrate, whereas the rash of Lyme disease shows numerous plasma cells. No serological testing for STARI is available; results of tests for B burgdorferi are generally negative. It is generally recommended that patients with STARI be treated with an oral antibiotic. Doxycycline (100 mg bid for 14 to 21 days) for patients 8 years and older, amoxicillin (50 mg/ kg/d in 3 divided doses for children; adult dosage is 500 mg tid), and cefuroxime (children, 30 mg/kg/d in 2 divided doses; adult dosage is 500 mg bid) can be used. This child completed a 21-day course of amoxicillin and had an uneventful recovery.

Acknowledgment: Dr J. Owen Hendley assisted with the identification of this child’s illness as STARI.

References:

REFERENCES:1. Masters EJ, Grigery CN, Masters RW. STARI, or Masters disease: Lone Star tick-vectored Lyme-like illness. Infect Dis Clin North Am. 2008;22:361-376, viii.
2. Blanton L, Keith B, Brzezinski W. Southern tick-associated rash illness: erythema migrans is not always Lyme disease. South Med J. 2008;101:759-760.
3. Centers for Disease Control and Prevention. Southern Tick-Associated Rash Illness. http://www.cdc.gov/ncidod/dvbid/stari. Accessed August 14, 2009.