Author(s): Yang Degang 1 2 , Kazuaki Nakamura 1 3 , Takeshi Akama 1 , Yuko Ishido 1 , Yuqian Luo 1 , Norihisa Ishii 1 , Koichi Suzuki [*] 4
immunity; lepra reaction; leprosy; macrophage; Mycobacterium leprae
Leprosy is caused by Mycobacterium leprae , which primarily parasitizes tissue macrophages in the dermis and the Schwann cells of peripheral nerves [1-4] . In many countries, leprosy has been successfully eliminated; however, it still remains a major public health problem in several countries even after multidrug therapy (MDT) was introduced. Thus, although its prevalence has declined over recent decades, 232,857 new cases (four cases/100,000 population) were detected worldwide in 2012  . Among WHO regions, the largest amount of cases were reported from southeast Asia (166,445 cases), which includes India (134,752 cases) and Indonesia (18,994 cases). Brazil also reported 33,303 cases in 2012. Both new cases and prevalence of leprosy demonstrate wide variation in numbers reflecting an unequal distribution of the disease. In fact, new cases reported from only 16 countries account for 95% of the total cases in the world  .
Leprosy displays a clinical spectrum that is determined by the host immunological response against M. leprae  . Differential recognition of viable or dead M. leprae in the natural course or during antibacterial therapy will be one of the factors that determine such immune reactions. In this article, we will briefly overview several aspects of epidemiological and clinical situations of leprosy mainly with regard to immune responses against M. leprae . In particular, we will discuss the potential role of the liver, which may help to understand the clinical manifestation of leprosy as well as open new therapeutic modalities. Perspectives on the new therapy of type II lepra reaction are also included.
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  . 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  . 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  .
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...