Case of tick-associated rash illness caused by Amblyomma testudinarium

We report a case of tick-associated rash illness (TARI), a new clinical entity of erythema migrans associated with a tick bite without infection of Lyme borreliosis agent. The patient, a 53-year-old man, went hiking in a mountainous area of Minoh City, Osaka Prefecture in October 2012. An erythematous macule with itching and a biting tick was found on his left thigh 2days later, which gradually expanded. On the first visit to our department at the fifth day after hiking, an erythematous macule of 10cm was recognized around the bite site. He had no systemic symptoms, and laboratory data were within normal limits. The tick was identified as a nymph of Amblyomma testudinarium. Histopathologically, perivascular infiltrates, mainly consisting of T lymphocytes, were seen in the dermis. The skin rash disappeared within 2weeks with no treatment. Serum antibody titers against Lyme disease borrelial and rickettsial agents on the first visit and 2weeks later were negative. These results indicate that the skin lesion of TARI was not associated with borrelial or rickettsial infection but a T-cell-mediated allergic reaction to salivary gland substances of the tick.