Leprosy

• 1. Introduction

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  In the 1980s, 5.2 million people around the world were living with leprosy. By 2020, that figure had fallen below 200,000. Leprosy, also called Hansen's disease, is a long-term infection caused by the bacterium Mycobacterium leprae, or by a close relative, Mycobacterium lepromatosis. It can damage the nerves, the skin, the eyes and the respiratory tract. It is not highly contagious, and people with leprosy can live with their families and attend school and work. Yet for centuries a diagnosis meant being set apart from everyone else. How does a bacterium that is so hard to catch end up taking feeling, fingers and sight? Where did it come from, and how did animals as unlikely as armadillos and red squirrels end up in its story? Why did fear of it shape laws, faith and whole institutions? And what finally changed, so that a course of pills now cures it?

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• 2. Nerves Under Attack

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  About 30% of people with leprosy suffer nerve damage, and nerves are where the disease does its worst work. The bacteria bind to Schwann cells and can strip nerves of their ability to carry signals, a process called demyelination. The body's own inflammatory response adds to the injury. Small sensory fibers in the skin go first, and the affected area may lose its hair and stop sweating.

  The first visible sign is often a pale or pink patch of skin that may not feel heat or pain. Losing the sense of pain, known as nociception, leads to the disease's most feared outcome. A person who cannot feel a cut or a burn keeps injuring the same hand or foot, and unnoticed wounds become infected. Cartilage is gradually absorbed into the body, and fingers and toes shorten and deform.

  The average incubation period is five years. Symptoms can appear within a year or take 20 years or more. Nerve damage can be reversed when treatment starts early. Delay treatment by several months and the damage becomes permanent.

  Doctors sort the disease by how many bacteria are present. A person with five or fewer pale, numb patches has the paucibacillary form. More than five patches means multibacillary disease. At the mild tuberculoid end of the spectrum, bacteria are scant or absent, and this is the most benign form. At the lepromatous end, bacilli fill the lesions in large numbers, and advanced cases can lose their eyebrows and lashes. The Ridley-Jopling scale describes five gradations along this spectrum.

  A skin patch with definite loss of sensation is the key clue. It separates leprosy from look-alikes such as tinea versicolor. Most diagnoses are made from symptoms alone, without laboratory tests. A diagnosis that arrives when a visible disability is already present counts as late. In countries where leprosy is rare, such as the United States, doctors often do not think of it, and that delay is exactly what lets nerve injury become permanent.

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• 3. Hard to Catch

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  Ninety-five percent of the people exposed to Mycobacterium leprae never develop leprosy. The bacterium has low pathogenicity, which means it rarely succeeds in causing disease. Shaking hands or sitting beside someone with leprosy does not spread it. Transmission needs close, extensive contact.

  The likely route is the upper airway. Bacilli in secretions from the nose or a cough are inhaled by another person. Older research pointed to the skin as the main route, but newer work favors the respiratory one. Scientists still cannot say how important the skin and the lining of the nose are as exit routes for the bacteria.

  Leprosy is not passed on through sex, and it does not pass from a mother to her unborn child. Seventy-two hours after a person begins appropriate multidrug therapy, they are considered non-infectious.

  Living with a person who has leprosy raises the risk of illness by 5-8 times compared with the general population. The disease is more common among people living in poverty. Malnutrition, other illnesses and genetic mutations can weaken immune function and add risk. Infection with HIV does not appear to do so.

  Cases often cluster in families, and several genetic variants have been identified. In many exposed people, the immune system clears the bacteria early, before serious symptoms develop. A defect in cell-mediated immunity may leave someone open to illness after exposure. Immune response also shapes which form a person gets. A strong cellular response contains the bacteria, while a weaker one allows large bacterial loads and wide spread through the body. One region of DNA tied to this variability is also involved in Parkinson's disease, which has led to speculation that the two disorders are linked at the biochemical level.

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• 4. Squirrels and Armadillos

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  In 1971, armadillos were first shown to develop leprosy after being inoculated with M. leprae. Their low body temperature lets their tissues hold enormous numbers of the organisms. Between 15 and 20% of Mexican long-nosed armadillos in the south-central United States carry the bacterium. Their armor makes skin lesions hard to spot, and abrasions around the eyes, nose and feet are the most common signs.

  Genetic typing of armadillo strains suggests they were of human origin for at most a few hundred years. That points to early European explorers of the Americas, from whom armadillos probably picked up the organism by accident. The infection then persisted in the armadillo population. It may be passing back to people, which would make leprosy a zoonotic disease. Humans can acquire it by handling armadillos or eating their meat, though the mechanism is not fully understood.

  Armadillos are also valuable to researchers. They have served as models for studying nerve damage, and their nerve function has been assessed with conduction tests. Meanwhile, many people fear them as dangerous, and in parts of America it has become more common to eat raw or undercooked armadillo, which raises the chance of infection.

  In November 2016, red squirrels in Great Britain, a threatened species there, were found to carry leprosy. Nonhuman primates, including African chimpanzees, sooty mangabeys and cynomolgus macaques, have also been infected naturally. Red squirrel fur was highly prized and intensively traded in the medieval period. That trade has been suggested as a cause of the leprosy epidemic in medieval Europe.

  A pre-Norman skull dug up at Hoxne, in Suffolk, in 2017 carried DNA from a strain of M. leprae that closely matched the strain in modern red squirrels on Brownsea Island. Even so, wild squirrels do not appear to pose a high risk to people. The last known human case of leprosy arising in the United Kingdom was recorded over 200 years ago.

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• 5. Ancient Traces

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  At Balathal, in Rajasthan, northwest India, skeletal remains found in 2009 hold the oldest documented evidence of leprosy, dating to the 2nd millennium BC. The discoverers were cautious. If the disease traveled from Africa to India in the 3rd millennium BC, they wrote, more skeletal and molecular evidence would be needed to confirm an African origin.

  A tomb at Akeldama, beside the Old City of Jerusalem, held the shrouded body of a man from the first half of the 1st century. Researchers from the Hebrew University of Jerusalem recovered DNA from the remains and proved the case. In 2005, geneticists using comparative genomics traced the disease from East Africa or the Near East along human migration routes, including routes of trade in goods and slaves. They found four strains of M. leprae, each concentrated in particular regions of the world.

  Then came older strains from Great Chesterford, in southeast England, dating to AD 415-545. They suggest another path for the spread and hint that leprosy may have originated in Western Eurasia. They also show that Europe held more strains at the time than researchers had assumed.

  Written records are harder to read. Early sources such as the Indian Atharvaveda, the Egyptian Ebers Papyrus and passages of the Hebrew Bible are ambiguous. The Indian doctor Sushruta's Compendium describes leprotic symptoms, and it dates to around 600 BC in its original form. Hippocrates may have described symptoms consistent with leprosy in 460 BC. Yet the disease probably did not exist in Greece or the Middle East before the Common Era.

  In Norway in 1873, Gerhard Armauer Hansen identified M. leprae as the cause of the disease. It was one of the first pathogenic bacteria ever identified. The name leprosy itself comes from the Greek lepra, tied to lepis, meaning scale. In 2008 a second cause, M. lepromatosis, was found. DNA studies show it lives mainly in the Americas and was there before Europeans arrived. The disease reached Polynesia late, probably not until the middle of the 19th century.

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• 6. Sacred and Unclean

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  The Hebrew word tsaraath covered far more than one illness. Under the law of Leviticus 14:54-57, it took in any progressive skin condition, along with mold or discoloration on clothing, leather and the walls of houses. The Talmud treats it as lesions or stains linked to ritual impurity. Jewish authorities, past and present, describe it as a spiritual ailment with no direct connection to Hansen's disease. The link comes from translations of the Hebrew text into Greek and the misconceptions that followed.

  All three Synoptic Gospels describe Jesus healing people with leprosy, in Matthew 8:1-4, Mark 1:40-45 and Luke 5:12-16. Leviticus 13:44-46 calls the person unclean but stops short of a moral judgement. Later readers were less restrained. Some early Christians believed God was punishing sinful behavior, and in the 6th century Pope Gregory the Great and Isidore of Seville considered people with the disease to be heretics. In India, skin diseases translated as leprosy appear in the Atharva Veda by 600 BC. The Manusmriti, from 200 BC, forbade contact with those infected and made marriage to such a person punishable.

  In the Eastern Roman Empire, church leaders faced a growing health problem and tried to change how society saw it. Gregory of Nazianzus preached sermons urging Christians to help the afflicted. He condemned anyone who rejected them on the claim that God had sent the disease as punishment. Church leaders also began to say "holy disease" instead of "elephant's disease," suggesting the illness purified people for heaven. No cure was found, but patients could receive palliative care and were never expressly banned from society. In the 12th century, the Constantinople jurist Theodore Balsamon noted that people with leprosy could enter the same churches, cities and assemblies as healthy people.

  In the late 6th century, bishops in France, including at Chalon-sur-Saône, worked to set up permanent places to house and feed people with leprosy. By the 12th and 13th centuries, France alone had nearly 2,000 leprosaria. The rise may reflect growing cities and crusaders returning from the Middle East. The third Lateran Council of 1179 required people with leprosy to have their own priests and churches. A 1346 edict by King Edward expelled them from city limits. They were often made to wear identifying clothing or carry a bell announcing their approach.

  Leprosaria were not prisons. Residents went out to beg for alms to support the house, and they met with their families. The stigma, however, outlasted the sick themselves. Groups in medieval Western Europe, such as the Cagots and the Caquins, faced discrimination justified in part by claims that they descended from lepers.

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• 7. Isolation and Medicine

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  In 1832, Dr. JJ Hjort carried out the first leprosy survey in Norway, laying a basis for epidemiological surveys. Later surveys produced a national registry to track the rate of infection. Norwegian scientists Daniel Cornelius Danielssen and Carl Wilhelm Boeck led early research across Europe, which led to the National Leprosy Research and Treatment Center. They believed the disease was hereditary. That view fed arguments for isolating the infected by sex, to prevent reproduction.

  By the 1860s, leprosy was declining in the Western world, yet authorities still embraced isolation. Their reasons included fear of the disease spreading from the Global South, the efforts of Christian missionaries, and a poor grasp of bacteriology and contagion. English surgeon Henry Vandyke Carter saw isolation in Norway and applied it in British India, with money and logistical help from Protestant missionaries. In 1898 the colonial government there passed the Leprosy Act, which forced people with leprosy into asylums, separated by sex. The act proved hard to enforce, and India repealed it in 1983.

  The National Leprosarium at Carville, Louisiana, was the only leprosy hospital in the mainland United States. Patients from across the country were sent there, away from the public. Carville became known for innovations in reconstructive surgery. In 1941-22 patients there took part in trials of a new drug called Promin. The results were described as miraculous.

  Before that, leprosy was believed to be highly contagious and was treated with mercury. For centuries, chaulmoogra tree oil was applied to the skin. Swallowed, it caused nausea, and injected, it formed an abscess. In 1915, Alice Ball discovered how to make the oil water-soluble, and patients improved markedly. Promin was followed by dapsone in the 1950s, then clofazimine and rifampicin in the 1960s and 1970s. When bacteria began to resist dapsone in the 1960s, recorded cases ran to tens of millions.

  The Indian scientist Shantaram Yawalkar and his colleagues combined rifampicin and dapsone to curb resistance. In 1981, the World Health Organization first recommended all three drugs together. Until multidrug therapy arrived in the early 1980s, leprosy could not be diagnosed and treated successfully within the community. The regimen runs six months for paucibacillary disease and 12 months for multibacillary disease. It comes in calendar-labelled blister packs, which makes it easy to use in the field. Rifampicin is given monthly because it speeds up the body's breakdown of dapsone.

  Between 1995 and 1999, the WHO, with the Nippon Foundation, supplied free multidrug therapy to every endemic country. Donations from the manufacturer Novartis later extended the free supply in 2000, 2005-2010 and 2015. For people living with a patient, a single dose of rifampicin is associated with a 57% reduction in infections within 2 years. A vaccine called LepVax entered clinical trials in 2017, with results from 24 participants published in 2020. If it succeeds, it would be the first vaccine made specifically for leprosy.

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• 8. Stigma and Survivors

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  Josefina Guerrero, a Filipino spy in the Second World War, turned fear into cover. She used the Japanese fear of her leprosy to listen in on battle plans, then passed the information to American forces under Douglas MacArthur. Most people with the disease have met that fear with far less reward.

  In Brazil, folklore holds that leprosy is carried by dogs, linked to sexual promiscuity, or sent as punishment for sin. Domestic workers can lose their jobs as the signs of the disease appear. In extreme cases in northern India, leprosy is equated with an untouchable status that, in one description, "often persists long after individuals with leprosy have been cured of the disease, creating lifelong prospects of divorce, eviction, loss of employment, and ostracism from family and social networks." Until 2019, a diagnosis of leprosy was legal grounds for an Indian spouse to petition for divorce. Fear of such outcomes delays people from seeking treatment, and people with leprosy face a higher risk of problems with mental well-being.

  Some lives became symbols. Baldwin IV of Jerusalem, who lived from 1161 to 1185, ruled as the "Leper King" of Latin Jerusalem. The Belgian priest Damien De Veuster caught the disease while ministering on Molokai in the Kingdom of Hawaii, where people with leprosy lived under government-sanctioned quarantine. Josephine Cafrine of Seychelles had leprosy from age 12, and her journal was published as an autobiography in 1923. The Indian actress Dimple Kapadia was diagnosed a few months before filming the 1973 musical romance Bobby, recovered completely, and built a successful career.

  Art has tried to look directly at the disease. The Iranian poet Forugh Farrokhzad made a 22-minute documentary about a leprosy colony, The House Is Black. It opens with the statement that there is no shortage of ugliness in the world, but that by closing our eyes to ugliness we will intensify it. Stephen R. Donaldson, author of The Chronicles of Thomas Covenant, drew on time in India, where his father worked at a mission for people with leprosy.

  In 2019, India reported 114,451 new cases, 57% of the world's total. The World Health Organization has kept an Expert Committee on Leprosy since 1954, the same year World Leprosy Day began. Its definition of elimination is modest on paper: fewer than one case per 10,000 people in a community.

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