Subclinical infections are common, as demonstrated by a positive burulin skin test. There is no specific race predilection. There are no differences in rates of infection among males and females. Lesions usually begin as singular, painless, occasionally pruritic, subcutaneous nodules, which appear approximately 7-14 days after trauma to the overlying skin. Suppuration and ulceration occur within 1 or 2 months.
Characteristic lesions have a scalloped border and a sloughing, necrotic base.
Undermining necrosis along the panniculus may extend several centimeters. Culture M ulcerans can be cultured from ulcer exudate or fresh tissue. Pathologic specimens reveal extensive coagulation necrosis in the dermis and subcutaneous fat, with destruction of cutaneous nerves, blood vessels and cutaneous appendages. The necrosis may extend well beyond the edges of the ulceration. There is an abundance of extracellular clumps of acid-fast bacilli, usually seen at the base of the ulcer and in the surrounding necrotic tissue.