Causes of leprosy

The causative agent of human leprosy is Mycobacterium leprae (M. leprae hominis, M. Hanseni), described in 1874 by G. Hansen, and belongs to the genus Mycobacterium.

The morphology of the leprosy pathogen has been studied on fixed preparations using light and electron microscopes. The typical form of mycobacteria leprosy is straight or slightly curved rods with rounded ends, 1 to 4-7 μm long and 0.2-0.5 μm wide. Granular, branched and other forms of the pathogen are also observed. They are immobile, do not form spores or capsules, are acid- and alcohol-resistant, gram-positive, and stain red according to Ziehl-Neelsen. They are located intra- and extracellularly, tend to group together, located parallel to each other ("cigarette packs"). They can be in the form of spherical clusters (globi), 10-100 μm in diameter, sometimes about 200 μm. In terms of morphology, tinctorial and antigenic properties, the causative agent of human leprosy is very similar to mycobacterium tuberculosis.

Mycobacterium leprae is an obligate intracellular parasite localized in the cytoplasm of cells of the reticuloendothelial system and tissue macrophages. It has a tropism for the skin and peripheral nerves. It reproduces by dividing the mother cell into two daughter cells by ingrowth of the transverse septum. A pure culture of the pathogenic agent has not been obtained, since Mycobacterium leprae does not grow on nutrient media. Only after S. Shepard (1960) developed a method for experimentally infecting laboratory mice with human leprosy, and W. Kirchheimer and E. Storrs (1971) - nine-banded armadillos (Dasypus novemcinctus Linn.), did it become possible to more broadly study the biology and biochemistry of Mycobacterium leprae, obtain diagnostic and vaccine preparations, test new drugs, and determine the drug resistance of the leprosy pathogen. There are reports of susceptibility to human leprosy mycobacteria in the seven-banded armadillo, Korean chipmunk and turtles.

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Epidemiology of leprosy

Leprosy is still widespread in many countries. Its endemic foci are found in Asia, Africa, South and Central America, Europe, mainly in countries with low levels of material security, general and sanitary culture. Currently, the number of people with leprosy on the globe is 10-15 million. The overall prevalence rate is 1.33 per 1000 population.

Traditionally, it is believed that the only reservoir and source of leprosy infection is a sick person. The most contagious are patients with lepromatous and borderline forms of leprosy. However, recently, data have been obtained indicating that some animal species can also be a reservoir of leprosy mycobacteria: the nine-banded armadillo, chimpanzee, some other species of monkeys and certain species of arthropods. Their possible role in the transmission of leprosy to humans is being studied. The main route of transmission of infection is airborne (through mucous membranes). The possibility of leprosy infection through damaged skin and blood-sucking insects is allowed. Vertical transmission of infection is not observed: children of patients with leprosy are born healthy.

Adults are relatively resistant to leprosy. Of those who had long-term contact with sick people in the family, approximately 10-12% fell ill. Cases of occupational infection with leprosy, according to foreign literature, were isolated. Children are more susceptible to leprosy infection. In most cases, leprosy infection occurs in early childhood with long-term and constant contact of a child with a leprosy patient. The incidence of leprosy is the same for men and women.

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