leprosy leprosy leprosy, also known as hansen's disease (hd), is a long-term infection by the bacteria mycobacterium leprae or mycobacterium lepromatosis. infection can lead to damage of the nerves, respiratory tract, skin, and eyes. this nerve damage may result in a lack of ability to feel pain, which can lead to the loss of parts of a person's extremities from repeated injuries or infection through unnoticed wounds. an infected person may also experience muscle weakness and poor eyesight. leprosy symptoms may begin within one year, but, for some people, symptoms may take 20 years or more to occur. leprosyother nameshansen's disease (hd)rash on the chest and abdomen caused by leprosypronunciation/ˈlɛprəsi/ specialtyinfectious diseasessymptomsdecreased ability to feel paincausesmycobacterium leprae or mycobacterium lepromatosisrisk factorsclose contact with a case of leprosy, living in povertytreatmentmultidrug therapymedicationrifampicin, dapsone, clofaziminefrequency209,000 (2018) leprosy is spread between people, although extensive contact is necessary. leprosy has a low pathogenicity, and 95% of people who contract m. leprae do not develop the disease. spread is thought to occur through a cough or contact with fluid from the nose of a person infected by leprosy. genetic factors and immune function play a role in how easily a person catches the disease. leprosy does not spread during pregnancy to the unborn child or through sexual contact. leprosy occurs more commonly among people living in poverty. there are two main types of the disease – paucibacillary and multibacillary, which differ in the number of bacteria present. a person with paucibacillary disease has five or fewer poorly-pigmented, numb skin patches, while a person with multibacillary disease has more than five skin patches. the diagnosis is confirmed by finding acid-fast bacilli in a biopsy of the skin. leprosy is curable with multidrug therapy. treatment of paucibacillary leprosy is with the medications dapsone, rifampicin, and clofazimine for six months. treatment for multibacillary leprosy uses the same medications for 12 months. a number of other antibiotics may also be used. these treatments are provided free of charge by the world health organization. leprosy is not highly contagious. people with leprosy can live with their families and go to school and work. in the 1980s, there were 5.2 million cases globally but they went down to less than 0.2 million by 2020. most new cases occur in 14 countries, with india accounting for more than half. in the 20 years from 1994 to 2014, 16 million people worldwide were cured of leprosy. about 200 cases per year are reported in the united states. separating people affected by leprosy by placing them in leper colonies still occurs in some areas of india, china, the african continent, and thailand. leprosy has affected humanity for thousands of years. the disease takes its name from the greek word λέπρᾱ (léprā), from λεπῐ́ς (lepís; 'scale'), while the term "hansen's disease" is named after the norwegian physician gerhard armauer hansen. leprosy has historically been associated with social stigma, which continues to be a barrier to self-reporting and early treatment. some consider the word leper offensive, preferring the phrase "person affected with leprosy". leprosy is classified as a neglected tropical disease. world leprosy day was started in 1954 to draw awareness to those affected by leprosy. signs and symptoms common symptoms present in the different types of leprosy include a runny nose; dry scalp; eye problems; skin lesions; muscle weakness; reddish skin; smooth, shiny, diffuse thickening of facial skin, ear, and hand; loss of sensation in fingers and toes; thickening of peripheral nerves; a flat nose from destruction of nasal cartilages; and changes in phonation and other aspects of speech production. in addition, atrophy of the testes and impotence may occur. leprosy can affect people in different ways. the average incubation period is five years. people may begin to notice symptoms within the first year or up to 20 years after infection. the first noticeable sign of leprosy is often the development of pale or pink coloured patches of skin that may be insensitive to temperature or pain. patches of discolored skin are sometimes accompanied or preceded by nerve problems including numbness or tenderness in the hands or feet. secondary infections (additional bacterial or viral infections) can result in tissue loss, causing fingers and toes to become shortened and deformed, as cartilage is absorbed into the body. a person's immune response differs depending on the form of leprosy. approximately 30% of people affected with leprosy experience nerve damage. the nerve damage sustained is reversible when treated early, but becomes permanent when appropriate treatment is delayed by several months. damage to nerves may cause loss of muscle function, leading to paralysis. it may also lead to sensation abnormalities or numbness, which may lead to additional infections, ulcerations, and joint deformities. paucibacillary leprosy (pb): pale skin patch with loss of sensation skin lesions on the thigh of a person with leprosy hands deformed by leprosy cause m. leprae and m. lepromatosis main articles: mycobacterium leprae and mycobacterium lepromatosis m. leprae, one of the causative agents of leprosy: as an acid-fast bacterium, m. leprae appears red when a ziehl–neelsen stain is used. m. leprae and m. lepromatosis are the mycobacteria that cause leprosy. m. lepromatosis is a relatively newly identified mycobacterium isolated from a fatal case of diffuse lepromatous leprosy in 2008. m. lepromatosis is indistinguishable clinically from m. leprae. m. leprae is an intracellular, acid-fast bacterium that is aerobic and rod-shaped. m. leprae is surrounded by the waxy cell envelope coating characteristic of the genus mycobacterium. genetically, m. leprae and m. lepromatosis lack the genes that are necessary for independent growth. m. leprae and m. lepromatosis are obligate intracellular pathogens, and cannot be grown (cultured) in the laboratory. the inability to culture m. leprae and m. lepromatosis has resulted in a difficulty definitively identifying the bacterial organism under a strict interpretation of koch's postulates. while the causative organisms have to date been impossible to culture in vitro, it has been possible to grow them in animals such as mice and armadillos. naturally occurring infection has been reported in nonhuman primates (including the african chimpanzee, the sooty mangabey, and the cynomolgus macaque), armadillos, and red squirrels. multilocus sequence typing of the armadillo m. leprae strains suggests that they were of human origin for at most a few hundred years. thus, it is suspected that armadillos first acquired the organism incidentally from early american explorers. this incidental transmission was sustained in the armadillo population, and it may be transmitted back to humans, making leprosy a zoonotic disease (spread between humans and animals). red squirrels (sciurus vulgaris), a threatened species in great britain, were found to carry leprosy in november 2016. it has been suggested that the trade in red squirrel fur, highly prized in the medieval period and intensively traded, may have been responsible for the leprosy epidemic in medieval europe. a pre-norman era skull excavated in hoxne, suffolk, in 2017 was found to carry dna from a strain of mycobacterium leprae, which closely matched the strain carried by modern red squirrels on brownsea island, uk. risk factors the greatest risk factor for developing leprosy is contact with another person infected by leprosy. people who are exposed to a person who has leprosy are 5–8 times more likely to develop leprosy than members of the general population. leprosy also occurs more commonly among those living in poverty. not all people who are infected with m. leprae develop symptoms. conditions that reduce immune function, such as malnutrition, other illnesses, or genetic mutations, may increase the risk of developing leprosy. infection with hiv does not appear to increase the risk of developing leprosy. certain genetic factors in the person exposed have been associated with developing lepromatous or tuberculoid leprosy. transmission transmission of leprosy occurs during close contact with those who are infected. transmission of leprosy is through the upper respiratory tract. older research suggested the skin as the main route of transmission, but research has increasingly favored the respiratory route. transmission occurs through inhalation of bacilli present in upper airway secretion. leprosy is not sexually transmitted and is not spread through pregnancy to the unborn child. the majority (95%) of people who are exposed to m. leprae do not develop leprosy; casual contact such as shaking hands and sitting next to someone with leprosy does not lead to transmission. people are considered non-infectious 72 hours after starting appropriate multi-drug therapy. two exit routes of m. leprae from the human body often described are the skin and the nasal mucosa, although their relative importance is not clear. lepromatous cases show large numbers of organisms deep in the dermis, but whether they reach the skin surface in sufficient numbers is doubtful. leprosy may also be transmitted to humans by armadillos, although the mechanism is not fully understood. genetics name locus omim gene lprs1 10p13 609888 lprs2 6q25 607572 park2, pacrg lprs3 4q32 246300 tlr2 lprs4 6p21.3 610988 lta lprs5 4p14 613223 tlr1 lprs6 13q14.11 613407 not all people who are infected or exposed to m. leprae develop leprosy, and genetic factors are suspected to play a role in susceptibility to an infection. cases of leprosy often cluster in families and several genetic variants have been identified. in many people who are exposed, the immune system is able to eliminate the leprosy bacteria during the early infection stage before severe symptoms develop. a genetic defect in cell-mediated immunity may cause a person to be susceptible to develop leprosy symptoms after exposure to the bacteria. the region of dna responsible for this variability is also involved in parkinson's disease, giving rise to current speculation that the two disorders may be linked at the biochemical level. mechanism most leprosy complications are the result of nerve damage. the nerve damage occurs from direct invasion by the m. leprae bacteria and a person's immune response resulting in inflammation. the molecular mechanism underlying how m. leprae produces the symptoms of leprosy is not clear, but m. leprae has been shown to bind to schwann cells, which may lead to nerve injury including demyelination and a loss of nerve function (specifically a loss of axonal conductance). numerous molecular mechanisms have been associated with this nerve damage including the presence of a laminin-binding protein and the glycoconjugate (pgl-1) on the surface of m. leprae that can bind to laminin on peripheral nerves. as part of the human immune response, white blood cell-derived macrophages may engulf m. leprae by phagocytosis. in the initial stages, small sensory and autonomic nerve fibers in the skin of a person with leprosy are damaged. this damage usually results in hair loss to the area, a loss of the ability to sweat, and numbness (decreased ability to detect sensations such as temperature and touch). further peripheral nerve damage may result in skin dryness, more numbness, and muscle weaknesses or paralysis in the area affected. the skin can crack and if the skin injuries are not carefully cared for, there is a risk for a secondary infection that can lead to more severe damage. diagnosis testing for loss of sensation with monofilament in countries where people are frequently infected, a person is considered to have leprosy if they have one of the following two signs: skin lesion consistent with leprosy and with definite sensory loss. positive skin smears. skin lesions can be single or many, and usually hypopigmented, although occasionally reddish or copper-colored. the lesions may be flat (macules), raised (papules), or solid elevated areas (nodular). experiencing sensory loss at the skin lesion is a feature that can help determine if the lesion is caused by leprosy or by another disorder such as tinea versicolor. thickened nerves are associated with leprosy and can be accompanied by loss of sensation or muscle weakness, but muscle weakness without the characteristic skin lesion and sensory loss is not considered a reliable sign of leprosy. in some cases, acid-fast leprosy bacilli in skin smears are considered diagnostic; however, the diagnosis is typically made without laboratory tests, based on symptoms. if a person has a new leprosy diagnosis and already has a visible disability caused by leprosy, the diagnosis is considered late. in countries or areas where leprosy is uncommon, such as the united states, diagnosis of leprosy is often delayed because healthcare providers are unaware of leprosy and its symptoms. early diagnosis and treatment prevent nerve involvement, the hallmark of leprosy,