Mycobacterium leprae -- Leprosy

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Pathogenic Microbiology in Italy [1]

"Mycobacterium leprae" globi in patient. From: Escholarship.org [2]

Woman with leprosy. From: Leprosymission.org [3]

Etiology/Bacteriology

Taxonomy

| Domain = Bacteria | Phylum = Actinobacteria | Class = Actinobacteridae | Order = Actinomycetales | Suborder = Corynebacterineae | Family = Mycobacteriaceae | Genus = Mycobacterium | Species = M. leprae |

NCBI: Taxonomy Genome: Mycobacterium leprae

Pathogenesis

Transmission

Although much about the transmission of Mycobacterium leprae is unknown, prolonged contact with an infected person increases an individual's chance of becoming infected. Armadillos can harbor the bacteria, but are not seen as a threat to human contraction of the disease. In addition, insects could be possible carriers of Mycobacterium leprae but this is unclear In humans, the bacteria is thought to be passed through skin and nasal mucosa (WHO). One study has demonstrated that large numbers of the bacteria can be found on the skin of infected persons, providing a possible means of transmission (Job). Mycobacterium leprae could also be passed through nasal mucosa like the closely related Mycobacterium tuberculosis (Nature).

Infectious dose, incubation, and colonization

Mycobacterium leprae is not able to be cultured in the lab, which can hinder studies of infectious dose and incubation, however some sources provide estimates for these categories (Review). With a doubling time of 14 days (Shephard), Mycobacterium leprae has the longest doubling time of any studied bacteria (Nature). The World Health Organization states that Mycobacterium leprae has an incubation period of an average 5 years. Humans and armadillos are currently the only known reservoirs of the bacteria, with infected humans accounting for up to 7 billion organisms per gram of tissue (WHO). Mycobacterium leprae mostly lives in the extremities and facial region within macrophages and Schwann cells of the peripheral nervous system (Nature).

Epidemiology

Map of new leprosy cases annually (2010) From: Leprosymission.org [4]

Mycobacterium leprae is thought to have originated in East Africa and spread across the globe through human migratory trends, reaching the Western world within the last 500 years (Monot). In 2012, the World Health Organization recorded a prevalence of approximately 180,000 cases (WHO). Through eradication efforts, the total number of cases worldwide has decreased, yet the number of new cases each year has remained consistent (Review). Mortality is difficult to measure with leprosy, as the infection is not the immediate cause of death in many cases (WHO).

Clinical features

Clinical manifestations of "Mycobacterium leprae" infection. From: Bio.davidson.edu [5]

Treatment

Before and after Multidrug Therapy (MDT) From: Stlukesleprosyhospital.org [6]

References

1 Conway, Tyrrell. “Genus conway”. “Microbe Wiki” 2013. Volume 1. p. 1-2.

Created by Gracen Conway, student of Tyrrell Conway at the University of Oklahoma.