M. lepraemurium was first described by Stefansky as the caus-ative agent of leprosy in rats in 1901 at Odessa. The rat leprosy was found in 4–5% of slaughtered rats investigated during an attack of human plague. The condition, subsequently, has been documented with variable incidence from different countries of the world. M. lepraemurium resembles M. leprae and is found in the mononuclear cells of the subcutaneous tissues, lymph nodes, and in the nodules in the lungs and liver of the infected rat. However, both M. lepraemurium and M. leprae are not related species, and they differ from each other as shown by DNA studies.
M. lepraemurium is cultivated with difficulty in Ogawa’segg-yolk medium (pH 5.8–6.3) at 37°C and also in rat fibro-blasts cell lines.
M. lepraemurium in rats causes rat leprosy, which ischaracterized by two forms: glandular form and muscu-locutaneous form. Enlarged, hard, and whitish inguinal, axillary, and cervical lymph nodes are found in the glan-dular type, and ulceration and loss of hair are found in the musculocutaneous type. The bacteria do not cause disease in humans.