What Is Leprosy?

Leprosy (Hansen’s Disease), is a chronic infectious disease that primarily affects the peripheral nerves, skin, upper respiratory tract, eyes, and nasal mucosa. The disease is caused by a bacillus (rod-shaped) bacterium known as Mycobacterium leprae.


The Bacterium: Mycobacterium leprae

M. leprae, discovered by G.A. Hansen in Norway in 1873, is a slow-growing, intracellular pathogen that cannot live outside its host. Because it can only be grown in animals, not in a laboratory, it is more difficult to study than other bacteria. Armadillos and immunocompromised mice are the two primary sources for growing the bacteria for research purposes.


The Disease

The disease is widely assumed to be spread via the respiratory system through nasal droplets. Because M. leprae survive best at low temperatures, it primarily affects the superficial sites of the skin and peripheral nerves.

Leprosy usually affects the skin, peripheral nerves, and upper airways but has a wide range of clinical manifestations. Clinical forms of leprosy represent a spectrum reflecting the cellular immune response to M. leprae. Patients with good T-cell immunity (Th1 type) towards M. leprae exhibit tuberculoid (TT) leprosy which is also known as pauci-bacillary leprosy, a milder form of the disease, characterized by skin discoloration. Those with poor T-cell immunity towards M. leprae typically exhibit lepromatous (LL) leprosy or multi-bacillary leprosy, which is associated with symmetric skin lesions, nodules, plaques, thickened dermis, and frequent involvement of the nasal mucosa resulting in congestion and nose bleeds. In between these forms of leprosy are the borderline tuberculoid (BT), borderline-borderline (BB) and borderline lepromatous (BL) forms.

LL leprosy is also characterized by large numbers of organisms in the skin, many skin lesions with slight hypopigmentation, and less sensory loss in the lesions. While people with LL have high titer antibodies to M. leprae, they also have an impaired cellular immune response to the bacillus. Changes in immunity of the host as well as treatment can result in worsening of the clinical course of the disease.

Sometimes leprosy may cause some degree of peripheral neurological damage (nerve damage in the arms and legs) that causes sensory loss in the skin as well as muscle weakness. People with long-term leprosy may lose the use of their hands or feet due to repeated traumatic injury resulting from lack of sensation. If left untreated, it can cause progressive and permanent damage to the skin, nerves, eyes, and limbs.

Treatment

The disease is completely curable with MDT treatment,which is freely available in all government skin clinics in Sri Lanka. For pauci-bacillary leprosy treatment is given routinely for 6 months and for multi-bacillary leprosy treatment is given routinely for 12 months.