Symptoms, Types, and Molecular Mechanisms of Leprosy
To assess whether or not one has leprosy, medical staff will generally take skin biopsies or skin smears for a bacterial indices. This examination of pieces of skin and skin liquid will show presence of bacteria on a scale of 0 to 6, with 6 being more than a 1000 per sample. Other assessments include mouse foot pad drug sensitivity, where the bacteria on the skin are cultured in the mouse foot pad and treated with leprosy drugs for a response; PCR assays for the M. leprae genome; and antibody assays for the phenolic glycolipid (PGL-1) antigen. The lepromin test, introduced by Mitsuda in 1916, uses dead M. leprae to measure the intensity of the cell-mediated immune response
The most common first signs are dark spots that are of different texture, size and color than normal skin and are usually hairless and numb. These lesions usually involve the cooler tissue of the body, including the skin, the superficial nerves, the nose, pharynx, larynx, eyes and testicles in men. The infection usually starts by an attack on the Schwann cells, which leads to a demyelination of the nerve sheaths, effectively slowing communication to the brain. Alpha dystroglycan, a Schwann cell receptor on M. leprae, interacts with the nerve cell , using the assistance of PGL-1, a protein in the cell wall which also assists in demyelination. Recently, it has been found that the fibronectin-attachment protein is important in the initial colonization of these Schwann cells. Inside the Schwann cell phagocytotic vacuole, the bacteria are free to reproduce without interference from antibodies and macrophages, as Schwann cells lack lysosomal enzymes. This eventually causes a numbness and loss of sensation which can be extremely dangerous. In many cases, hands, feet, and even limbs have had to be amputated because secondary infections have ravaged the extremities without any communicable pain. Nerve damage also includes the loss of the blinking reflex in the eyes leading to possible blindness, thicking of the nerves, neuritis, ulcers, loss of bone, shortening of digits, abnormal neurologic sensations, facial disfigurement and appearance of erythematous subcutaneous nodules (1-5 cm diam.) and lesions (1-10 cm diam.). M. leprae are also able to penetrate the perineural tissues and induce bacteremia.
The World Health Organization lists 3 types of leprosy, including tuberculoid, lepromatous and indeterminate leprosy. Indeterminate is the simplest form. It is symptomized by a single lesion which, upon non-treatment, can develop into the more severe other forms. Tuberculoid leprosy, or paucibacilliary Hansen�s Disease, occurs as 58% of new cases and is a benign and non-progressive form that is symptomized by one to five asymmetrical lesions. These lesions are well-defined and are hypopigmented, or pale. Other symptoms include muscle atrophy, general loss of sensation, nerve compression, and clawed limbs. This form is self-limiting and sufferers can heal. However, in rare instances, the disease can get worse and become lepromatous leprosy. Sometimes, tuberculoid leprosy is broken down into two categories, major and minor. The major version includes more defined margins and has partially healed areas on the lesions. Nerve damage starts early and continues on; if left untreated, it will lead to destruction of the nerves, loss of sensation and eventually paralysis to that area. In the case of tuberculoid leprosy, the lepromin test is always positive. Skin smears are usually negative, showing that the disease is non-infectious and basically a closed case � the disease will run its course, but progress no further.
Cell-mediated immunity is intact throughout the infection and violent immune reactions result. Differentiated macrophages help localize the infection and isolate the bacteria for phagocytosis. They can collect normal antigenic information and act as antigen presenting cells, or APC�s. In collaboration with MHC Class II antigen recognition, the rest of the immune process is stimulated. In leprosy, some of the macrophages are transformed into epithelioid cells, which have tightly interdigitated cell membranes in zipper-like arrays linking adjacent cells. With the assistance of helper T cells, the epithelioid cells barricade the bacteria and prevent its spread by creating granulomas. These granulomas are made up of a central core of dead tissue where most of the bacteria are held, which is surrounded by epithelioid cells and further ringed by T and B lymphocytes, dendritic cells, neutrophils, extracellular tissue, fibrotic tissue and calcified areas. Those who are unable to form granulomas usually succumb to the lepromatous form. The epithelioid cells can also combine into so-called giant cells that are also part of the immune defense. The two cytokines interleukin-2 and interferon-gamma are markers of the cell-mediated immune response in tuberculoid leprosy.
However, the pathogenic bacilli have effective evasion mechanisms against phagocytotic digestion that allow them to survive. Before binding, the bacilli can release di- or tri-acetylated lipoarabinomannan enzyme that blocks macrophage ability to respond to the activating effects of interferon-gamma and interleukin-2, which are the major markers of cell-mediated immune respone in tuberculoid leprosy. They are released by CD4 helper T lymphocytes after antigen stimulation. Lipoarabinomannan is normally a part of the bacillar envelope and may play a role in coordinating activity with other mycobacteria. Another method of avoiding binding is to surround itself with phenolic glycolipid and scavenge free radicals to prevent antigen recognition. Also, the infected cells usually lose efficiency as antigen-presenting cells and thus are not recognized for phagocytosis. After it is bound, however, and delivered to the phagosomes, the bacilli can still escape and multiply in the cytoplasm.
Lepromatous leprosy, otherwise known as multibacilliary leprosy, is a malign and progressive form that exists as 42% of new cases. Many symmetrical lesions occur, ranging in size from big to small, as macules, papules and nodules. Symptoms include a condition called leonine facies that consists of thinned eyebrows and ridged foreheads; skin ulceration, otherwise known as Lucio�s phenomenon; thickened dermis; slow symmetric nerve involvement; abundant bacteria in lesions; bacteremia, where bacteria has entered otherwise sterile blood; infiltrated epiglottis; blindness or glaucoma; fibrosis; bone degradation; stiffness; destroyed testes in males; nerve palsies, or paralysis, of the facial, ulnar, median, radial, tibeal and peroneal nerves; loss of finger by neurotrophic atrophy, nasal congestion, epistaxis and secondary infections. Though nerve damage starts late in lepromatous leprosy, bacterial infestation is large and the perineurium or surrounding nerve tissue gets very inflamed at an early stage. Lepromin skin tests are negative and demonstrate little or no resistance to leprosy. Conversely, skin smears are positive.
Only a weak cell-mediated immune response is present with lepromatous leprosy. In fact, the skin is infiltrated with suppressor T cells which release interleukin-4, which acts to stop the natural immune reaction. M. leprae is able to enter the macrophages by binding with the receptors and creating a replicative phagosome. It is known that plasma membrane cholesterol is important for this mechanism, but it is not clear exactly what role it plays. The macrophages do not act as normal APC�s, but they may still invoke partial lysis of the bacteria. However, the engulfed bacteria phospholipids can still survive within their cytoplasmic vacuoles and create cytoplasmic droplets or lepra cells. It must be understood that the lepra cells are not reservoirs of still viable bacteria. The partial lysis is caused by a lysosomal phospholipase enzyme defect which leads to a metabolic disease which stifles the immune response. It is also thought that the oxidative phosphorylation defect of the mitochondria within the macrophage contributes to the inability to lyse the bacteria completely and the proliferation of free radicals, which contribute to tissue damage. Sulfone drugs like Dapsone, discussed later, are thought to reverse this inability to lyse and neutralize the free radicals.
With a weakened immune response, the macrophages can become merely a transport for the bacteria and allow the disease to circulate around the body and infiltrate into the brain and other parts of the body that it would not normally infest. These infected macrophages pass bacteria to each other by use of membrane tethers. Uninfected macrophages are infected by migration and engulfing of infected specimens, thus infecting itself. Dendritic cells are also likely to help in transport of the bacteria. Recently, epithelial cells have been implicated in inducing transcytosis and infected macrophage migration across the epithelium. The replicative phagosome created communicates with early endosomes of the host endocytic machinery and acquires its components from cell surface plasma membrane and early endosomes. It does not fuse to lysosomes and become acidified, because this would kill it. Somehow, the bacteria has evolved to be able to restrict phagosomal fusion. Some biopsies have shown infiltrated macrophages collecting at the epithelium and at the roots of sweat-making and hair cells. Some of these macrophages create lysosomes which bound to phagosome and become phagolysosomes with a characteristic foaminess, thus their name: foamy cells.
Eventually, these can cause pressure atrophies that pucker the skin and inhibit sweat and hair growth. The lepra cells, mentioned earlier, can be effectively phagocytosed later on in disease development and the humoral immune response stimulated to remove the bacteria. This usually involves interleukin-4, the main marker of humoral immunity, which incites humoral immune-linked T lymphocytes.
Prophylaxis and Treatment
Since ancient times, the oil of the chaulmoogra nut was used to treat leprosy. It tended to be very painful and its long term benefits were extremely questionable. In the fifties, this treatment was dropped in favor of drugs that were first found effective in tuberculosis and were now being tested or designed for leprosy. Today, leprosy is treated with sodium hydrocarpate, minocycline, ofloxacin, and clarithromycin, but it is most commonly treated with the trio dapsone, rifampicin and clofazimine in what is known as Multi Drug Therapy or MDT. MDT was suggested for use by Yawalkar in 1974 and approved by WHO in 1982 after extensive clinical studies, especially Languillon�s 1979 study using dapsone and rifampicin. Its record is awesome; it has decreased global prevalence by 85% in the past 15 years and has proven to be the most cost-effective treatment because it eliminates contagion after the first dose and eliminates recurrence once the regimen is complete. By mid-2001, MDT cured over 11 million patients. Those with indeterminate leprosy are told to take 600 mg of dapsone, 400 mg ofloxacin and 100 mg minocycline. Tuberculoid leprosy sufferers are told to take 50-100 mg of dapsone daily for 6-12 months and 600 mg of rifampicin monthly for the same length of time. Borderline lepromatous lepers take the same regimen, for 2 years. Those with full-blown lepromatous leprosy have the most vigorous regimen. They must take 50-100 mg of dapsone daily, 600 mg of rifampicin monthly, 50-200 mg of clofazimine daily and 300 mg of clofazimine monthly as a backup, over a period of 2 years.
Dapsone, or di-amino diphenyl sulfone, was synthesized by Fromm and Wittmann originally as a treatment for tuberculosis. Its effectiveness for leprosy was first proven by Guy Faget in 1941 when it was used in the form of Promin. In 1946, it was introduced to the public after Cochrane treated his patients in India with intramuscular injections of dapsone. Dapsone, as do other members of the sulfone family, stops mycobacterial replication and also has a weak bactericidal effect on M. leprae. Side effects include mild anemia, skin rashes, and more rarely, peeling skin conditions, increased numbers of reticulocytes or immature blood cells, peripheral neuropathy, nausea, nephritic syndrome, erythema nodosum leprosum, and hemolysis in cases of glucose-6-phosphate dehydrogenase deficiency, an enzyme in the glycolytic pathway. Its individual usage was limited in 1974 when Waters demonstrated the existence of dapsone-resistant bacteria. This promoted the development of MDT and alternative therapies because of the panic this news caused.
Rifampicin was introduced in 1968 as Rimactane by CIBA Limited. Liker and Kamp verified its efficiency in 1970. Its active ingredient is rifamycin S, a slightly degraded and more stable form of rifamycin B, the fermentation product of rifamycin. Rifamycin is an antibiotic found in Streptomyces mediterranei. It is non-toxic and can inhibit prokaryotic DNA synthesis. However, its most important role is as a bactericide, where it eliminates 99.9% of targeted bacteria within 3 months. Side effects include abnormal liver tests for the length of treatment, harmless orange color in urine, sweat and tears, nephritis, rashes, thrombocytopenia and a flu-like syndrome. Like dapsone, its individual use was limited after the discovery of rifampicin-resistant bacteria in 1976 by Jacobson and Hastings.
Clofazimine (G30320) was discovered in 1957 by Barry in the labs of J.R. Geigy Ltd. with the help of Trinity College, Dublin. It was proven effective in 1963 by Browne and sold under the trademark Lamprene in 1969. At first, it was seen as a disappointment as it only worked on tubercular mice and not humans; however, its ability to inhibit growth of leprosy bacteria in mice could be extrapolated to humans. It too is non-toxic, inhibits DNA replication and displays a weak bactericidal effect. It exerts an anti-inflammatory effect in controlling erythema nodosum leprosum, and also promotes phospholipase A2 synthesis, which can act on the bacterial phospholipids in the lepra cells of lepromatous leprosy. Side effects include darkening of skin, increased sensitivity to sunlight, upset stomach, discoloration of feces and bodily secretions and rarely, hepatitis or liver disease. It too is limited for individual use after the discovery of clofazimine-resistant bacteria in 1982, by Warndorff-van Diepen.
Most treatment plans also involve prevention and management of economic and social realities for the patient. Hospitals and volunteer treatment organizations often offer a comprehensive health education to the patient, family and neighborhood, including warnings to constantly check for signs of lesions, numbness and infection. Sometimes, economic rehabilitation workshops are held to decrease personal stigma and find sources of self-worth and employment for the patient. MDT is used, as well as certain corticosteroids to limit nerve damage, pre-fabricated finger and foot splints and reconstructive surgery to halt and correct limb disabilities, physiotherapy to prevent worsening of deformities, electrical muscle stimulation to prevent muscle atrophy, epoxy grip-aids to assist in daily tasks, and frequent eye exams to prevent blindness.
During treatment, reactions can occur. These occur in roughly 25% of cases, and are reactions to the dead and dying leprosy bacillus within the body. It is not a setback; it is actually a good sign. Usual symptoms include redness, swelling, neuritis, ulceration and silent neuropathies. Corticosteroids such as prednisolone are prescribed until the reaction stops. However, if treatment does not start before six months, it cannot reverse the nerve damage. Another frequent reaction is erythema nodosum leprosum, or ENL, which is thought to be a disorder caused by the interaction between antibodies and the cytokines, IL-2 and TNF-alpha. It is characterized by fever, erythematous tender nodules, neuritis, edema, arthralgia, leukocytosis, iridocyclitis, pretibial periostitis, orchitis and nephritis. It is usually treated with thalidomide, found effective in 1965 by Sheskin. Thalidomide is teratogenic. It is thought to work by its inhibition of TNF-alpha mRNA. However, ENL can also be treated with clofazimine or the corticosteroids.
A couple vaccines do exist, with variable success rates between 0 and 80% The idea behind vaccines is that prevention is much better than curing. The first vaccine to come into existence was the Bacille Calmette-Guerin (BCG) vaccine, derived from the tuberculosis mycobacteria and originally the tuberculosis vaccine. It offers a 50% reduction in leprosy risk and remains effective for 10 years. It is diluted, and is not made stronger because strengthening the vaccine might actually lead to re-infestation. Another vaccine has been made from M. leprae DNA. The coding for certain parts and proteins are inserted into various vectors and injected into mice to retrieve the protein products that result. These proteins are supposed to bring about immunity, and actually works as well as the BCG vaccine. A March 2003 paper discussed the possibility of a vaccine based on the newly discovered susceptibility gene on chromosome 6q25. In 1998, the National Institute of Immunology in India released a vaccine for multibacilliary leprosy based on the Mycobacterium W strain. This vaccine had a 25.7% success rate and was prepared from non-pathogenic fast-growing soil strains of mycobacteria. These bacteria were used to stimulate immune responses toward M. leprae because both of them have cross-matching antigens. The Central Drug Research Institute in Lucknow, India, developed a vaccine based on another strain of mycobacteria, the Mycobacteria Habana. Other preparations of cultivable mycobacteria are under development.
Two other vaccines show remarkable success rates. The vaccine made at the Indian Cancer Research Institute in Mumbai, India, in 1979, was created from gamma-irradiated bacilli that created a stable immune conversion for 5 years. It induced a change in lepromin status in 55% of lepromatous patients, from negative to positive. In the studies, it showed an average 65.5% success rate. The armadillo-derived vaccine made by IMMLEP, was based on heat-killed M. leprae (HKML), and had an average 64% success. After testing, it was found capable of inducing delayed-type hypersensitivity in mice and guinea pigs. Along with BCG, it was found to be capable of upgrading the immune status of leprosy sufferers.
The Leprosy Song, sung to Yesterday
Leprosy,
Bits and pieces falling off of me�
But it isn�t the toxicity,
It�s just neglect of injury!
Suddenly,
I�m not half the man I used to be.
Can�t feel anything peripherally
From swollen nerves, hypersensitivity..
Why don�t leprae grow in vitro, we cannot say�
In vivo they grow very slow, once in 12 day-ay-ay-ays�
Hard to get,
But the stigma hasn�t faded yet.
Don�t keep an armadillo as a pet,
Clofazimine and Dpasone, don�t forget!