What is the value of polymerase chain reaction (PCR) in the diagnosis of leprosy?

Leprosy Mailing List – April 14^th, 2011

Ref:  What is the value of polymerase chain reaction (PCR) in the diagnosis of leprosy?
From: C. Smith, Aberdeen, U.K.

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 Dear Dr Noto,

The role of PCR in the diagnosis of leprosy is an important question and I have heard the question asked many time recently.  Over the past 20 years there has been a growing body of literature on PCR in leprosy – much of it on the development and validation of the methods, and various ad hoc studies have been published.  The possibility of including PCR in the diagnostic criteria for leprosy was recently debated but in the end it was agreed that there was not sufficient evidence – the presence of M. leprae by PCR alone was not sufficient evidence to diagnose leprosy as studies show contacts, and indeed members of the community, can be positive by PCR without having any other evidence of disease or going on to develop the disease.   The same is the case with other infections.  But it is clear that PCR can have value in certain circumstances and there are a number of useful studies recently, if not definitive, certainly important.

The JALMA group (1) in India have evaluated the use of PCR from slit skin smears in children where skin biopsies were not possible – they found 13 PCR positives in 20 smear negative children.  In Brazil (2) a study evaluated PCR results from buccal swabs in large numbers of patients (18% positive) and contacts (7% positive), they also looked at anti PGL1 status.  A further recent study in India (3) used PCR to assess over 400 contacts and followed them for 2 years where 2 PCR positive contacts developed disease. 

With the growing evidence, there is a case for a review of the literature to determine the role of PCR in the diagnosis of leprosy and the interpretation of a positive PCR in people with no other signs of disease.

Best regards,

Cairns Smith

1.   Kamal R, Natrajan M, Katoch K, Katoch VM.  Evaluation of diagnostic role of in situ PCR on slit-skin smears in pediatric leprosy. Indian J Lepr. 2010 Oct-Dec;82(4):195-200.

2.   Martinez TS, Figueira MM, Costa AV, Gonçalves MA, Goulart LR, Goulart IM  Oral mucosa as a source of Mycobacterium leprae infection and transmission, and implications of bacterial DNA detection and the immunological status. Clin Microbiol Infect. 2010 Dec 31. doi: 10.1111/j.1469-0691.2010.03453.x. [Epub ahead of print]

3.   Banerjee S, Sarkar K, Gupta S, Mahapatra PS, Gupta S, Guha S, Bandhopadhayay D,Ghosal C, Paine SK, Dutta RN, Biswas N, Bhattacharya B. Multiplex PCR technique could be an alternative approach for early detection of leprosy among close contacts--a pilot study from India. BMC Infect Dis. 2010 Aug 24;10:252