Short item Published on March 10, 2016

Understanding leprosy trends

Visitors to Robben Island, near Cape Town, South Africa, will pass the sad remnant of a facility for individuals suffering from leprosy, which closed in 1931 (1). The disease we call leprosy today, or Hansen’s disease, is now known to be caused by a simple bacterium, Mycobacterium leprae (2), in the same genus as the tuberculosis bacillus. Like many other bacterial infections, leprosy can be cured with a course of antibiotics (3). Yet it seems to have cast a long shadow across this world, in both space and time (4). Many societies report long histories of stigma against individuals presenting the disease (5). Individuals with the disease were frequently consigned to a life apart (5), often in such facilities as on Robben Island, or Carville, in the United States.

In the 1940s, successful chemotherapy with newer compounds began to replace earlier, relatively futile, treatments (6). By the 1980s, the WHO recommended relatively short course combination therapy based on rifampicin, dapsone, and clofazimine (7). In 1991, the World Health Organization declared “WHO’s commitment to continuing to promote the use of all control measures including multidrug therapy together with case-finding to attain the global elimination of leprosy as a public health problem by the year 2000”, where elimination of leprosy as a public health problem was explicitly defined as “the reduction of prevalence to a level below one case per 10 000 population” (8).      Despite occasional controversy, a tremendous amount seems to have been achieved (9, 10). As of 2014, a world of over seven billion people counts fewer than a quarter of a million cases, with over half in hugely populous India (11). Yet the number of new cases is not declining as had been hoped, and in 2013, a meeting sponsored in part by the Nippon Foundation noted an apparent “stagnation” (12).

Our group, which included SACEMA researchers, grew out of the Meaningful Modeling of Epidemic Disease Clinic hosted by AIMS Muizenberg in June of 2015 (J. Pulliam, A. Welte, PIs). We took a statistical look at recent annual new case detection trends reported by the government of India’s National Leprosy Eradication Programme (NLEP) (13). Unlike most countries, India shares district-level case detection information with the world on a public website (14) (available from 2008 to the present). We used linear mixed effects regression to control for increased case finding efforts in selected districts as reported by the NLEP. All analysis and mapping were conducted in the R package (R Foundation for Statistical Computing, Vienna, Austria). We found evidence of a very slow declining trend, but with substantial differences between districts. Some districts with persistently higher new case detection rates are seen. Moreover, some districts show rising case counts over the last eight years, while others show falling counts. Because leprosy can show incubation periods of 2–10 years (15), rapid changes are probably attributable to changes in reporting or case finding. We found no evidence of association with tuberculosis case counts or with BCG vaccination rates (though with high and relatively uniform BCG coverage across most Indian states, we did not expect such an association to appear—despite solid evidence of the efficacy of BCG against leprosy.) Overall, our analysis found no evidence in favor of rapid progress in leprosy decline; extrapolation based on current trends suggests substantial changes would only take place on a time scale of decades. Our results support views that enhancements in current public health policy must be undertaken to hasten the decline of leprosy (16).

This article is based on the following publication Brook CE, Beauclair R, Ngwenya O, Worden L, Ndeffo-Mbah M, Lietman TM, Satpathy SK, Galvani AP, Porco TC. Spatial heterogeneity in projected leprosy trends in India. Parasit Vectors. 2015: 8:542. Cara Brook, Olina Ngwenya and Roxanne Beauclair made inputs in the current article. “Funding and other support is acknowledged in the original publication.”