A Vaccine for Leprosy

The Bacillus Calmette Guerin (BCG) Vaccine

The Bacillus Calmette Guerin (BCG) vaccine (photo courtesy of Pasteur Merieux Connaught, Canada).

Mycobacterium bovis BCG is the vaccine most studied in association with leprosy. The BCG vaccine is used as a vaccine against tuberculosis in many countries worldwide (not the U.S.) with variable efficacy. The effectiveness of the BCG vaccine in providing immunity against leprosy is quite controversial, however. Researchers have done complementary analysis of the BCG vaccine to see its effect on leprosy and levels of protection have varied from no effect to up to 80%. The BCG vaccine provides considerable efficacy against tuberculosis, however, there are distinct similarities and differences between M.tuberculosis and M.leprae (see below). Various factors such as biological differences in BCG strains, exposure to environmental mycobacteria, and ineffective boosting against reinfection with or reactivation of tuberculosis may give rise to the varying levels of efficacy of BCG against tuberculosis. These reasons may also suggest the variability of BCG against leprosy. The vaccine is a live, attenuated vaccine, meaning that it infects the individual but does not give them any disease (unless the person is immunocompromised). The BCG vaccine contains weakened forms of the organism M.tuberculosis through attenuation. The attenuated form of M.tuberculosis is obtained by serial passage or culture of the active organism in culture media or cells.

How different are M.tuberculosis and M.leprae?

Looking at the two mycobacteria on a stain, they appear very similar. They have similar cell walls and similar enzymatic capabilities. However, their chromosomes are sequenced quite differently. M.tuberculosis has about 4000 gene capabilities, and therefore a greater capability of making and degrading compounds. M.leprae has about 1600 genes. The two mycobacteria have about the same number of molecules.

Kiyana Harris, Class of 2007, kjharris@stanford.edu
Stanford University
Parasites & Pestilence: Infectious Public Health Challenges
Prof. D. Scott Smith, ssmith@stanford.edu