Leprosy
is almost exclusively a disease of the developing world, affecting areas of
Asia, Africa, Latin America, and the Pacific. While Africa has the highest
disease prevalence, Asia has the most cases. More than 80% of the world’s cases
occur in a few countries: India, China, Myanmar, Indonesia, Brazil, Nigeria, Madagascar,
and Nepal. Within endemic locales, the distribution of leprosy is quite uneven,
with areas of high prevalence bordering on areas with little or no disease. In
Brazil the majority of cases occur in the Amazon basin and two western states,
while in Mexico leprosy is mostly confined to the Pacific coast. Except as
imported cases, leprosy is largely absent from the United States, Canada, and
northwestern Europe. In the United States, ±4000 persons have leprosy and 100 to 200 new cases are
reported annually, most of them in California, Texas, New York, and Hawaii
among immigrants from Mexico, Southeast Asia, the Philippines, and the
Caribbean. The global prevalence of leprosy is difficult to assess, given that many
of the locales with high prevalence lack a significant medical or public health
infrastructure. Estimates range from 0.6 to 8 million affected individuals. The
lower estimate includes only persons who have not completed chemotherapy,
excluding those who may be physically or psychologically damaged from leprosy
and who may yet relapse or develop immune-mediated reactions; the higher figure
includes patients whose infections probably are already cured and many who have
no leprosy-related deformity or disability. Although the figures on the
worldwide prevalence of leprosy are debatable, it is generally agreed that the
annual incidence of new cases is rising (529,000 estimated new cases in 1995
and 719,000 in 2001, with 60% of the latter number from India alone).
Leprosy
is associated with poverty and rural residence. It appears not to be associated
with AIDS, perhaps because of leprosy’s long incubation period. Most people
appear to be naturally immune to leprosy and do not develop disease
manifestations following exposure. The time of peak onset is in the second and
third decades of life. The most severe polar form of leprosy is twice as common
among men as among women and is rarely encountered in children. The frequency of
the polar forms of leprosy in different countries varies widely and may in part
be genetically determined; certain HLA associations are known for both polar
forms of leprosy (see below). In India and Africa, 90% of cases are
tuberculoid; in Southeast Asia, 50% are tuberculoid and 50% lepromatous; and in
Mexico, 90% are lepromatous.
Source:
Harrison_s_Principles_of_Internal_Medicine_16th_Edition
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