Erythema chronicum migrans and salmon fishing in Alaska: an enigma resolved by microbiology laboratory

A 50-year-old man, pentathlete and fond of salmon fishing, after returning from Alaska was referred to our Division for an erythematous and indolent lesion on the right thigh gradually enlarging from the right knee to the right rear and the buttock.The patient was clinically diagnosed with figurate erythema. Laboratory analysis demonstrated a moderate leukocytosis and hypergammaglobulinemia, accompanied by serological markers of past contact with noted EBV and CMV.A “punch” biopsy of the edge of the lesion showed a superficial and deep perivascular and interstitial infiltrate of lymphocytes, eosinophiles and a few plasma cells, consistent with a borrelial infection. Lyme serology (IFI) suggested a questionable borderline positivity; subsequent investigations by ELISA and Western Blot were both positive, leading to the diagnosis of erythema chronicum migrans in course of borreliosis.The diagnosis was further confirmed by positive PCR for Borrelia burgdorferi sensu lato. The erythema resolved after a 2-week doxycycline treatment (2x100 mg die). The amplification product (16S rDNA gene) obtained from skin biopsy was sequenced using standard ABI technology, and confirmed the identification of a member of B. burgdorferi sensu lato (sl) complex. Since this sequence was not useful to identify the genospecies, further studies were conducted employing a nested PCR targeted on the internal transcribed spacer (ITS) of B. burgdorferi, following a protocol previously described (1). The ITS sequence showed 100% identity with B. afzelii, a species not reported from North America, thus prompting us to conclude that the patient was not infected by B. afzelii during the fishing trip in Alaska.