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Chapter: Microbiology and Immunology: Bacteriology: Mycobacterium leprae and Mycobacterium

Epidemiology - Mycobacterium leprae

Leprosy is a disease prevalent worldwide.


Leprosy is a disease prevalent worldwide.

 Geographical distribution

The worldwide prevalence of leprosy is 1 case/10,000 popula-tion. Most cases of leprosy are found in Southeast Asia, Africa, and the Americas. Fifteen endemic countries in these areas have a prev-alence of 1 case/10,000 populations. Leprosy is most endemic in Brazil, Angola, Central African Republic, Congo, Madagascar, Mozambique, Tanzania, Nepal, and India. Approximately 74% of these cases are found in these nine countries. Lepromatous leprosy is more prevalent in Africa, while tuberculosis is more frequent in Asia. In India, leprosy is present in all states and territories. Orissa and Bihar have a higher prevalence of more than 5 cases/1000 population, whereas Haryana has the least (0.1/1000 population). Overall, the prevalence of the disease has decreased since the introduction of short multidrug therapy in 1982.


In infected host, M. leprae is found in large number in infected nasal secretions of patients with lepromatous leprosy.

 Reservoir, source, and transmission of infection

Leprosy is an exclusively human disease. Humans are the prime reservoir of Mleprae. Nine-banded armadillo, chimpanzee, and mangabey monkeys are the three animal species known to be important animal reservoirs of leprosy. Leprosy is not a highly infectious disease. Lepromatous forms of the disease, but not the tuberculoid form, is infectious.

      Nasal secretions from patients with lepromatous leprosy are important source of infection. Very large numbers of lepra bacilli are shed in the nasal secretions. As high as 8 108 bacilli can be discharged during a single act of nose blow of the patients with untreated lepromatous leprosy.

      Inhalation of infectious aerosol and skin contact with respi-ratory secretions or wound exudates are the most important routes of infection in leprosy. The following observations sup-port transmission of infection through the respiratory route:

·           Large numbers of morphologically intact lepra bacilli are demonstrated in the nasal discharges.

·           The organisms have not been detected on the surface of the skin.

·           Lepra bacilli survive for several hours or days outside the human host.

·           Experimental transmission of leprosy has been achieved by aerosols containing M. leprae and by topical application in immunosuppressed mice.

Leprosy is usually not spread by means of direct contact through intact skin, though close contacts are more susceptible.

      Lepromatous leprosy is more common in men than women, with a male to female ratio of 2:1. Tuberculoid leprosy predom-inates in children. The disease is rare in infants.

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Microbiology and Immunology: Bacteriology: Mycobacterium leprae and Mycobacterium : Epidemiology - Mycobacterium leprae |

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