The prevalence rate is defined as the number of cases registered for MDT treatment among the population in which the cases have occurred, again at a given point in time. History
Historical distribution
Using comparative genomics, in 2005, geneticists traced the origins and worldwide distribution of leprosy from East Africa or the Near East along human migration routes. They found four strains of M. leprae with specific regional locations. Strain 1 occurs predominantly in Asia, the Pacific region, and East Africa; strain 4, in West Africa and the Caribbean; strain 3 in Europe, North Africa, and the Americas; and strain 2 only in Ethiopia, Malawi, Nepal, north India, and New Caledonia. This confirms the spread of the disease along the migration, colonisation, and slave trade routes taken from East Africa to India, West Africa to the New World, and from Africa into Europe and vice versa.Skeletal remains discovered in 2009 represent the oldest documented evidence for leprosy, dating to the 2nd millennium BC. Located at Balathal, Rajasthan, in northwest India, the discoverers suggest that, if the disease did migrate from Africa to India during the 3rd millennium BC "at a time when there was substantial interaction among the Indus Civilization, Mesopotamia, and Egypt, there needs to be additional skeletal and molecular evidence of leprosy in India and Africa to confirm the African origin of the disease."
This molecular test alone is not sufficient to diagnose a person, but this approach may be used to identify someone who is at high risk of developing or transmitting leprosy such as those with few lesions or an atypical clinical presentation. Classification
Several different approaches for classifying leprosy exist. There are similarities between the classification approaches. The World Health Organization system distinguishes "paucibacillary" and "multibacillary" based upon the proliferation of bacteria. ("pauci-" refers to a low quantity.) The Ridley-Jopling scale provides five gradations. The ICD-10, though developed by the WHO, uses Ridley-Jopling and not the WHO system. It also adds an indeterminate ("I") entry. In MeSH, three groupings are used. Leprosy may also occur with only neural involvement, without skin lesions. Prevention
Early detection of the disease is important, since physical and neurological damage may be irreversible even if cured. Medications can decrease the risk of those living with people who have leprosy from acquiring the disease and likely those with whom people with leprosy come into contact outside the home. The WHO recommends that preventive medicine be given to people who are in close contact with someone who has leprosy. The suggested preventive treatment is a single dose of rifampicin (SDR) in adults and children over 2 years old who do not already have leprosy or tuberculosis.