Leprosy as a Model of Immunity

Yang Degang; Kazuaki Nakamura; Takeshi Akama; Yuko Ishido; Yuqian Luo; Norihisa Ishii; Koichi Suzuki


Future Microbiol. 2014;9(1):43-54. 

In This Article

The Trend of Leprosy: Is Prevalence Reduced by Chemotherapy?

MDT is certainly effective to cure patients who have developed leprosy and, in fact, millions of patients have been treated by MDT since its introduction in the mid-1980s. Thus, MDT has had an astonishing record of curing disease. Without drug therapy, the disease in any patient would continue to advance, destroying more nerves and leading to increased deformity and disability. There were over 12 million registered cases of leprosy worldwide prior to the advent of MDT, and this has been reduced to just over 200,000 new cases per year currently.[5] Before we could jump to the seemingly obvious conclusion that MDT should be given all the credit for conquering leprosy, surprisingly, studies have failed to demonstrate a definite contribution of the current leprosy control strategy, which mainly relies on MDT to reduce leprosy.[7] Since patients are regarded as cured after MDT and removed from registration, the striking decrease in the prevalence of leprosy can been ascribed, at least in part, to a reduction in the duration of chemotherapy, from 24 to 12 months.[8]

In 1873, Armauer Hansen, a Norwegian physician, identified M. leprae as the etiological agent of leprosy, making leprosy the first human disease for which a bacterium was shown to be the causative agent. Leprosy was actually eliminated in Norway by 1920, 60 years before effective MDT was promoted worldwide and even earlier than the first effective antileprae drug, promin, was discovered in the 1940s. Certainly, improvements in nutrition, lowering poverty, rising incomes, decreasing the densities of those living in a single household and improvements in healthcare delivery are the main reasons why leprosy was eliminated in Norway and many other western countries long before the advent of any drug that could cure leprosy. An analysis of the time course of new case detection in Norway led to the conclusion that the effect physical isolation of affected patients has on the interruption of disease transmission was not clear.[7] These findings also led to the question of whether leprosy is finally cured solely by chemotherapy. An alternative explanation is that the disease is defeated by restored immunity derived from improvements in public health and nutrition in addition to the more direct effects of drugs to kill bacilli, which will be discussed later. However, it is also true that in high endemic areas where poverty, poor nutrition and poor healthcare delivery exist, MDT is absolutely necessary to cure leprosy.