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Leprosy, also known as Hansen's disease, is a chronic bacterial infection caused by Mycobacterium leprae, an obligate intracellular parasite. Although an ancient disease, leprosy continues to be a major health problem in the developing countries of Africa, Asia and Latin America. Several million people worldwide are permanently disabled by Hansen's disease. Although 95% of the global total of new cases were reported from 14 countries in 2013 (Bangladesh, Brazil, Côte d'Ivoire, Democratic Republic of the Congo, Ethiopia, India, Indonesia, Madagascar, Myanmar, Nepal, Nigeria, Philippines, Sri Lanka and Tanzania), 59% were from India alone. In these countries, infected humans are the only known natural reservoir, and M. leprae are thought to spread personto-person following long-term, close contact, usually with an infected member of the household who is excreting enormous numbers of leprosy bacilli in their nasal secretions. Nonetheless, only 5% of the world's population are naturally susceptible to infection with M. leprae.
Although rare, leprosy has been a reportable disease in the United States since 1970. In the past decade for which data are available (2004-2013), the number of new cases reported each year has been mostly fewer than 100 (average, 88.5 new cases yearly; range, 66-105). In the past decade, Hawaii reported a yearly average of 19.2 new cases, Texas 19.1, California 15.3 and Florida 8.4. The average number of new cases per year in Texas and Hawaii is consistent with the historical values for these states, but California shows a decreasing, and Florida an increasing, trend. For example, in the 12 years before 2006, Florida usually reported five or fewer cases yearly; but from 2007 to 2014, the state frequently reported 10 or more cases per year. The Florida Department of Health has recently reported 29 newly diagnosed cases in 2015. This represents a dramatic, almost threefold increase compared with the previous year.
In the laboratory, M. leprae has been grown in mouse footpads and in the 9-banded armadillo (Dasypus novemcinctus), but cannot be cultivated in vitro. The organism favors growth in cooler parts of the human body. Armadillos, due to their unusually low body temperature of 34°C (93°F) - similar to human skin - are particularly susceptible to leprosy, which becomes systemically disseminated. Following the discovery that armadillos were susceptible to M....