Leprosy is a disease caused by the bacterium Mycobacterium leprae. Due to its long incubation period, it is difficult to know where or when someone has caught the disease, though children are more likely than adults to contract it. Leprosy is common in many countries, especially in temperate, tropical, and subtropical climates. Symptoms of leprosy include skin lesions, muscle weakness, and numbness. It is not highly infectious, but is transmitted through droplets from close contact with infected persons. Although leprosy is curable and treatment is available, if left untreated, leprosy can cause progressive and permanent damage to the skin, nerves, limbs, and eyes.