Skin ulcers caused by Mycobacterium ulcerans in koalas near Bairnsdale, Australia.

Skin ulcers were found in 7 koalas from Raymond Island in the Gippsland Lakes of southeastern Australia. Ulcers in 4 koalas showed loss and underrunning of cutaneous tissue, with coagulative necrosis of subcutaneous tissue. These lesions contained large numbers of acid-fast bacilli, and areas of granulation tissue formation and superficial inflammation were present. Mycobacterium ulcerans was isolated from 2 of these animals. The ulcers from the other 3 koalas contained both M. ulcerans and M. scrofulaceum, and in these the necrotic tissue was surrounded by a granulomatous reaction which, in one case, extended into bone. Four of the koalas had more than one ulcer. The possible origin of the infections is discussed.