EPIDEMIOLOGY

Leprosy cases as of February 1992 (Aufderheide 142)

Despite experimental infections in mice and armadillos, humans remain the only known natural reservoir of Mycobacterium leprae (Bryceson 204). Due to the slow rate of M. leprae multiplication, an incubation of two to four years usually precedes the appearance of symptoms; however, periods ranging from three months to forty years have been reported (25). Studies conducted in India, which has long possessed one of the highest rates of incidence, indicates that one-third of clinical cases experience symptoms during childhood, while only 7% of patients developed an infection after the age of 35; U.S. figures are 10.1% and 43%, respectively (Aufderheide 142). Compounding the uncertainty regarding the manner of transmission and the variable nature of development is the fact that two-thirds of patients have no known contact with infected individuals ( Bryceson 209). The highest levels of prevalence are found in rural areas (Aufderheide 142).

Family members are the preferential targets of leprosy, though infection among close relatives is not inevitable: the transmission rate between spouses is 5-10%, though adult-to-child rates are five times greater (Aufderheide 142). Infants born to infected mothers possess bacillary antigens but do not develop the disease (Bryceson 209). Relatives of infected individuals do not appear to develop lepromatous leprosy more frequently than the general population; however, data derived from twin studies suggests the involvement of a genetic factor in people who do contract it (Bryceson 212).

World Health Organization prevalence figures list 219,826 cases of leprosy at the beginning of 2006. In 2005, the number of new cases was estimated to be 296,499, some 111,000 less than in 2004.

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