ABSTRACT
Mycobacterium leprae, the aetiological agent of leprosy in humans, gives rise to a chronic granulomatous disease that affects primarily the skin and peripheral nerves, and secondarily some internal organs such as the testis and the eye; viscera are seldom involved. Depending on host resistance, leprosy may present as a benign disease (tuberculoid leprosy) or as a malignant disease (lepromatous leprosy), with a spectrum of intermediate stages appearing between the two. Immunity against leprosy depends on the cell-mediated immunity of the host, and this is severely compromised in the malignant (lepromatous) form of leprosy. Although culture of M. leprae has never been achieved in artificial media, the bacterium may be grown in several experimental animals, including the armadillo, non-human primates, and to a certain extent, rodents. Naturally acquired leprosy has been reported in wild nine-banded armadillos (Dasypus novemcinctus) and in three species of non-human primates (chimpanzees [Pan troglodytes], sooty mangabey monkeys [Cercocebus atys] and cynomolgus macaques [Macaca fascicularis]), thus qualifying leprosy as a zoonosis. Murine leprosy is a leprosy-like disease of rats and mice, caused by Mycobacterium lepraemurium. The disease affects primarily viscera and the skin, and very rarely peripheral nerves. Depending on the host strain, rodent leprosy may also evolve as 'lepromatous' or 'tuberculoid' leprosy, and strains of mouse that develop intermediate forms of the disease may exist. Growth of M. lepraemurium on conventional media for mycobacteria is not successful, but the bacterium has been cultured on an egg yolk-based medium. Naturally acquired murine leprosy has been observed in rats, mice and cats, but not in humans or any other species. Thus, in contrast to human leprosy, murine leprosy is not a zoonosis.