Strain-typing of M. leprae

Leprosy Mailing List – May 31^st, 2011

Ref.:   Strain-typing of M. leprae

From: D M Scollard, T P Gillis, J L Krahenbuhl.  Baton Rouge, LA, USA

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Dear Salvatore,

We would like to thank Dr. Warren (LML May 16^th, 2011) for her interest in the strain-typing of M. leprae that was used in the study published about 3 weeks ago in the New England Journal of Medicine (abstract attached).  This has subsequently been reported in many newspapers around the world and, as she noted, different journalists had somewhat different ideas about this.  If you only read the news accounts it could be confusing. 

As Dr. Warren indicated, for many years it was not possible to identify different strains of M. leprae.  However, as a result of the sequencing of the entire genome ofM. leprae it has become possible, in the last 10 years or so, to identify a small number of differences in the genetic sequences of bacilli isolated from patients in different parts of the world.  This paper marks a major advance in this effort, combining two different molecular techniques to identify small differences in M. leprae DNA.  The result is that we now can, in fact, identify different strains of this organism. 

The investigators used these techniques to examine M. leprae DNA from wild-infected armadillos in the US and compared this with M. leprae DNA from human biopsies.  We found that almost all of the infected armadillos had the same strain ofM. leprae, and a majority of the US patients who had no foreign travel had the same ‘armadillo’ strain.  This indicates that humans and armadillos are sharing this infection, although the exact means of transmission is still unclear.  US patients with a history of foreign travel often had strains of M. leprae associated with other regions of the world. 

There are still many limitations to these strain-typing techniques, but it is clear that we are now at the beginning of an era in which we can use methods like this to ‘track’ different sources of infection with M. leprae, and this is a major advance for epidemiological studies of this disease.  However, determining “strains” by this technique in no way implies a functional difference in the groupings that would result in an altered pathogenic potential, i.e., all strains cause the same range of clinical types of leprosy. 

David M. Scollard, M.D., Ph.D.

Thomas P Gillis, PhD.

James L. Krahenbuhl, Ph.D.

National Hansen's Disease Programs

1770 Physicians Park Dr

Baton Rouge, LA 70816

http://www.hrsa.gov/hansens