The Bacteria of Leprosy
Above: Mycobacterium leprae in a skin section of a multibacillary leprosy patient. N is the nuclear material, M the plasma membrane, S the storage granules, W the cell wall, MS the mesosome.† Note that the black line is 0.2 nm in length.
Credit: R J
Name of bacteria: Mycobacterium leprae
Type of Bacteria: Acid-fast, rod-type (Bacillus); cannot be gram-stained
Disease Names: Leprosy, Hansenís Disease
Incubation: Difficult to assess in humans because exact time of exposure is usually unknown. Reportedly anywhere from 3 to 30 years (Noordeen 24).
Right: A graphical illustration of the Mycobacterium leprae bacterium and its internal structure.
Photo Credit: Mark Liao. 2006. Adapted from
Unique Features: It is impossible to culture the bacteria artificially (Gladwin 107), although it possible to grow on footpads of certain mice, primates and armadillos. Transmission is particularly difficult; even human trials to cause infection have not led to conclusive results. Is the only bacteria to infect schwann cells and peripheral nerves (Rees 33).
Size: 1-8 microns long, 0.3 microns in diameter (Rees 33)
Doubling Time: 11-13 Days, extraordinarily long for a bacteria (Rees 37).
Preferred temperature for growth: Less than 37 degrees Celsius.
Transmission of the Bacteria
Above: Although multibacillary leprosy patients, such as those above, are said to be infectious, the specific route of transmission is still unclear.
Photo Credit: Roy Pfaltzgraff, Clinical Leprosy, Leprosy. 1985
††††††††††† The study of leprosy transmission has been a frustrating one for researchers. Indeed, initial presumptions before the discovery of the bacterium usually focused on heredity or divine retribution. Humans are generally considered to be the only natural reservoir of leprosy, although the bacterium M. leprae has been detected in armadillos; it is unclear what role armadillos play in leprosy transmission. Deliberate infection of others is difficult, and the exact route of transmission is still being studied. The bacterium can be found in nasal secretions, as well as the skin surface. Reportedly, the bacterium can survive out of the body for more than 36 hours (Noordeen 23).† It appears that it is most likely that leprosy is transmitted through the respiratory route. In 2004, Achilles, et al., reported a case of accidental inoculation of M. leprae during a surgical procedure when the surgeon cut his finger during an open muscle biopsy of an undiagonised leprosy patient. Two years later, the surgeon developed paucibacillary leprosy. Other cases in the historical literature include apparent inoculation from tattoos in 1947 (Noordeen 23).†