Leprosy Diagnosis: An Update on the Use of Molecular Tools

Abstract

Leprosy is a chronic infectious disease caused by an obligatory intracellular mycobacteria Mycobacterium leprae, which presents tropism for Schwann cells and skin macrophages. Leprosy is a public health problem and early diagnosis is essential to avoid incapacities. The disease´s clinical presentation varies from few to widespread lesions and its diagnosis continues to be a challenge due to the low sensibility of the conventional methods, based on bacillary counts of skin smears and histopathology. Molecular techniques, especially the methods to identify M. leprae DNA based on polymerase chain reaction (PCR) have emerged as a support of the conventional methods for the analysis of clinical samples in difficult to diagnose cases, such as pure neural leprosy, indeterminate and paucibacillary leprosy. The technique has also proved useful in the study of leprosy transmission and monitoring résistance to the WHO recommended Multidrug treatment. Different biological samples can be analysed and there is no consensus in the molecular diagnostic techniques respect of the most efficient nucleic acid extraction method, most appropriate methodology and genetic target for PCR. These methods provide a very valuable option for confirmation of difficult clinical cases with scarce bacilli but requires a well-equipped laboratory and the high cost makes it inaccessible to be used as a routine diagnostic tool in most endemic countries.