Microbiology
Summary
Mycobacterium leprae is an acid-fast bacterium that causes leprosy. M. leprae thrives in cooler temperatures and resides in reservoirs like armadillos within the United States.
The two distinct clinical presentations of M. leprae infection are tuberculoid leprosy and lepromatous leprosy. Tuberculoid leprosy is associated with a strong TH1 immune response, leading to containment of the bacteria within macrophages; its symptoms are milder, presenting as well-demarcated, hairless, hypoesthetic skin plaques. On the contrary, lepromatous leprosy involves a predominant TH2 immune response, leading to a failed containment of the bacteria and a higher risk of human-to-human transmission. This form of the disease presents more severely, manifesting with "glove and stocking" neuropathy, numerous poorly demarcated raised lesions, and profound facial deformities collectively referred to as leonine facies. Treatment of leprosy requires multi-drug therapy over an extended period; tuberculoid leprosy treatment typically consists of dapsone and rifampin for 6-24 months, while lepromatous leprosy often requires dapsone, rifampin, and clofazimine for 2-5 years.
Lesson Outline
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FAQs
M. leprae is the bacterium responsible for leprosy, also known as Hansen's disease. Unlike most bacteria, it multiplies very slowly. Infection mainly affects the skin, peripheral nerves, mucosa of the upper respiratory tract, and eyes. It leads to symptoms such as skin lesions, sensory loss, weakness, and disfigurement if left untreated.
Tuberculoid and lepromatous leprosy represent two ends of the spectrum of disease manifestations of leprosy. Tuberculoid leprosy is the less severe form, characterized by a strong immune response that limits the growth of Mycobacterium leprae, leading to minor skin sores and nerve damage. Lepromatous leprosy is the more severe form due to a weak immune response; it is characterized by widespread skin lesions, nodules, and severe nerve damage.
M. leprae primarily survives and multiplies in humans who have not received treatment; however, some studies suggest that the bacteria may also survive in soil or in certain animals such as armadillos in the southern United States.
Leprosy is curable with a long-term course of multidrug therapy (MDT). The World Health Organization provides the treatment for free to all patients worldwide. The medications commonly used include dapsone, rifampicin, and clofazimine. These drugs kill the bacteria and help prevent disability. If the disease is detected early, further damage can often be prevented.
