Leprosy is caused by Mycobacterium leprae and has been known since biblical times. It
is still endemic in many regions of the world and a public health problem in Brazil.
The prevalence rate in 2011 reached 1.54 cases per 10,000 inhabitants in Brazil. The
mechanism of transmission of leprosy consists of prolonged close contact between
susceptible and genetically predisposed individuals and untreated multibacillary
patients. Transmission occurs through inhalation of bacilli present in upper airway
secretion. The nasal mucosa is the main entry or exit route of M. leprae. The deeper
understanding of the structural and biological characteristics of M. leprae, the
sequencing of its genome, along with the advances in understanding the mechanisms of
host immune response against the bacilli, dependent on genetic susceptibility, have
contributed to the understanding of the pathogenesis, variations in the clinical
characteristics, and progression of the disease. This article aims to update
dermatologist on epidemiological, clinical, and etiopathogenic leprosy aspects.