Mycobacterium ulcerans is a bacterium, which causes an ulcerative skin disease, known as Buruli ulcer. The mode of transmission of the infection to humans is unknown, although there is some evidence that it may be transmitted through the bites of infected aquatic insects. Buruli ulcer often starts as painless nodules, usually on the arms or legs. These then develop into large ulcers, with a whitish-yellowish base. Although most ulcers eventually heal, poorly managed patients may develop severe scars and local deformities, including disabling contractures. The disease occurs most frequently in children living in rural tropical environments, near wetlands. It can be treated with antibiotics and surgery.