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Germs that infect humans

Mycobacterium leprae

Mycobacterium leprae

© Dennis Kunkel Microscopy, Inc.

Microorganism: the bacterium responsible for leprosy is Mycobacterium leprae.

Disease: leprosy or Hansen’s disease

Occurrence of the disease

History: the first writings describing symptoms similar to those of leprosy come from India around 600 BC. The term "leprosy" is also mentioned in the Old and New Testaments. In 1873, a Norwegian by the name of Armauer Hansen demonstrated that the disease is caused by the bacterium Mycobacterium leprae, which prompted other studies on this disease. Dapsone was used for the first time as a treatment against leprosy in the 1940s. Before that, patients were diagnosed and isolated but no treatment was available.

Current situation: over ten million chronic cases of leprosy are identified around the world but they are mainly concentrated in tropical countries. In 1998 only three cases were reported in Canada.

Forecast: eradication of leprosy is predicted for 2005.

Mechanism of action of the microorganism: the bacteria usually penetrate into the organism by contact with nasal secretions of an infected person. The bacteria then invade the peripheral nerves including those of the skin skin, usually causing a severe rash.

Symptoms of the disease: pigmented rash followed by death of the cutaneous tissues, which causes a progressive loss of features of the face, fingers, toes, and other structures.

Incubation period: varies between nine months and 20 years

Contagious period: for treated patients, the contagious period lasts about three months.

Hosts: humans

Transmission: the exact mode of transmission is still unknown but prolonged contact with an infected person seems to be an important mechanism by which the disease spreads. Millions of bacteria are released each day in the nasal secretions of patients infected by leprosy.

Treatment: treatment requires a combination of three types of drugs (rifampin, dapsone and clofazimin) because many bacteria are now resistant to drugs used separately. The treatment lasts a minimum of 12 months.

Geographical distribution of the microorganism: certain endemic regions exist in southeast Asia, tropical Africa, and Latin America. However, new cases have been reported in the United States, mostly in California, Florida, Louisiana, and Texas.

Prevention: isolation of untreated patients

Vaccine: not available. However, BCG seems to protect against leprosy.