Infection by a bacterium called Mycobacterium ulcerans. The infection is most common in tropical and subtropical climates. The method of transmission is uncertain but the bacteria can enter the skin if it is broken (e.g. a cut) or it may possibly be transmitted by certain African aquatic insects or mosquitoes. The ulcers may become deep enough to affect the bone and can thus result in disability or deformity. See also Buruli ulcer