Southern tick-associated rash illness
STARI is a tickborne syndrome, vectored by the lone star tick (Amblyomma americanum). One case report described the spirochete Borrelia lonestari as the causative agent of STARI, but after extensive research, it has not been reproduced. Therefore, the etiology of STARI has not been confirmed, and this is merely speculation.
The disease is most commonly seen in the Southeastern and South Central United States, where A americanum ticks frequently bite humans. Cases are now being reported in several other regions. This disease should be considered an emerging health threat.
The estimated mean incubation period varies from 6.1 days to 9.2 days. The syndrome is characterized by an erythematous skin lesion with a central clearing, similar to erythema migrans, at the site of a lone star tick bite. These lesions may be single or multiple. Other symptoms include headache, fatigue, and myalgias.
CBC, basic metabolic panel, and liver function tests are usually unremarkable.
Treatment with antibiotics is recommended, and all symptoms resolve with tetracycline or amoxicillin.
Long-term sequelae or life-threatening complications have not been identified to date, but long-term follow-up studies evaluating the outcome following recovery from acute illness are lacking. Bites from A americanum have been associated with the subsequent development of allergies to mammalian meat (eg, beef, pork) in a small number of patients. It is thought that the allergy is mediated by induced immunoglobulin E (IgE) antibodies to alpha-gal (galactose-alpha-1,3-galactose), a mammalian oligosaccharide. Individuals with elevated IgE titers to alpha-gal have experienced urticaria, angioedema, and anaphylaxis symptoms either immediately or 3-6 hours (delayed onset) after ingesting mammalian meat (alpha-gal syndrome). Exactly how the tick bite leads to development of this allergy is unclear. Implicated tick bites have been noted to itch for 2 or more weeks. A blood test for these IgE antibodies exists.
A69.8 – Other specified spirochetal infections
444100007 – Southern tick-associated rash illness
Differential Diagnosis & Pitfalls
The skin rash in Lyme disease is classically more common on the extremities, and the target-like lesion has a mean diameter of 7 cm, whereas in STARI the skin lesions are often on the trunk and tend to be smaller, with a mean diameter of 4.5 cm.
In STARI, leukopenia, thrombocytopenia, anemia, and transaminitis are typically absent, while these abnormal labs are common findings in patients with Lyme disease.
Histology of the skin lesion in Lyme disease tends to show abundant plasma cell infiltrates, while in STARI lymphocytic infiltration predominates.
The diagnosis of Lyme disease by methods such as ELISA, immunofluorescent antibody test (IFA), and Western blot is useful and excludes STARI, which remains a clinical diagnosis.