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This man has leprosy. It is caused by the bacterium Mycobacterium leprae and symptoms include nerve damage, disfiguring sores, and slowly advancing debilitation. When exposed, children are more likely to catch the disease than adults. As you probably already know, in the past the disease had no cure and leper colonies were formed to separate those infected from the rest of the population to prevent spread of the disease. Now, the disease is actually rather easily treatable through the use of antibiotics and isolation is not needed. Treatment will make a person non-infectious and as such they can continue on with their lives without worry of spreading the disease to others. The earlier the disease is caught and treated, the less permanent damage will occur. There is, however, a growing concern as drug-resistant forms of the disease emerge.
Source is PubMed Health at the U.S. National Library of Medicine.