Leprosy in Ecuador and slit-skin smear examination

Leprosy Mailing List – October 2^nd, 2011

Ref.:   Leprosy in Ecuador and slit-skin smear examinationFrom: J A Barreto, Bauru, SP, Brazil

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Dear Drs Noto and Verduga,

Thank you very much to Dr Verduga for sharing with us these very interesting cases (see the attachment to LML Sept. 27^th, 2011).  Here in Brazil, where leprosy is highly endemic we also see similar cases quite commonly.  I would like do some comments, particularly about the skin smear technique.

The bacteriological index (BI) in lepromatous (LL) leprosy is usually 5+-6+, mainly when the smears are collected from nodules.  According to the Ridley & Jopling classification the BI ranges in a logarithmic scale from 0 to 6+, from tuberculoid (TT) to the LL forms of the disease.  Nevertheless, BI in skin smears commonly are 1+ lower than in biopsy bacteriological index (BBI).

I refer to your case number 5; LL leprosy with BI 3+ [you do not give information about the morphological index (MI)].  I have three points to comment about and, they are in relation with the apparently low BI (3+):-

1. How the smear was collected?  Was the dermis scraped after incision of the epidermis?  In Brazil, many physicians do not know that this must be done, becauseM. leprae is an intracellular parasite, and does not "flow in the lymph".

2. What was the concentration of Ziehl's fucsin: 1% or 0.3%?  In Brazil, I found that most laboratory technicians think that this is not important, what is wrong, because the resistance to distaining of the cell wall of M. leprae is weaker than M. tuberculosis, and therefore the use of the lower concentration (0.3%) of Ziehl's fucsin can lead to false negative results in cases of borderline leprosy, mainly when smears are not collected from lesions.

3. What was the concentration of alcohol-acid used to distaining the smear?  As well as the problem I have found above, and for the same reason, many laboratory technicians also do not know that the concentration must be lower, i.e., 1%, or this will lead to false negative results, even in lepromatous cases.

For many years, unfortunately, bacilloscopy, an important tool for the diagnosis, classification and follow up of leprosy was neglected by many leprosy control programmes in the world, and now many health professionals just don`t have knowledge about it.  Many even are afraid to become infected when collecting smears.

I hope that these comments be useful and I will be happy to know what other labororatories/programmes do.

Best regards,

Jaison A. Barreto

Dermatologist and Leprologist

Instituto Lauro de Souza Lima

Bauru, SP