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English: The transmission pathways of M. leprae. The M. leprae transmission pathways are not fully clear. However, an increased risk of human-to-human transmission because of intimate communication between untreated leprosy patients has been noted. Spreading via infectious aerosols is considered to be the most likely route of infection. M. leprae invades skin macrophages and Schwann cells, inducing skin lesions and neurological injury. Zoonotic transmission of M. leprae due to natural infection of armadillos in the Southeast United States has been reported, and humans and armadillos share a specific M. leprae strain. Red squirrels (Sciurus vulgaris) in the British Isles harbour M. leprae. Non-human primates including chimpanzees (Pan troglodytes) have been detected with leprosy in Africa and Asia. It has been speculated that potential vectors, such as amoebae, kissing bugs, and ticks, as well as the environment, could be potential transmission routes for M. leprae as a zoonotic disease. Black dotted arrows show confirmed transmission pathways. Grey arrows show hypothetical transmission pathways. Red dotted arrows show the main route of transmission between humans. An aerosol spreads the nasal secretions.