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Tuesday, April 23, 2019

Leprosy

From Wikipedia, the free encyclopedia

Leprosy
Other namesHansen's disease (HD)
Leprosy.jpg
A 24-year-old man with leprosy (1886)
Pronunciation
SpecialtyInfectious disease
SymptomsDecreased ability to feel pain
CausesMycobacterium leprae or Mycobacterium lepromatosis
Risk factorsClose contact with a case of leprosy, living in poverty
TreatmentMultidrug therapy
MedicationRifampicin, dapsone, clofazimine
Frequency514,000 (2015)

Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria Mycobacterium leprae or Mycobacterium lepromatosis. Initially, a person who is infected does not have symptoms and typically remains this way for 5 to 20 years. Symptoms that develop include granulomas of the nerves, respiratory tract, skin, and eyes. This may result in a lack of ability to feel pain, which can lead to the loss of parts of extremities due to repeated injuries or infection due to unnoticed wounds. Weakness and poor eyesight may also be present.

Leprosy is spread between people, although extensive contact is necessary. Spread is thought to occur through a cough or contact with fluid from the nose of a person infected by leprosy. It is not spread during pregnancy to the unborn children or through sexual contact. Leprosy occurs more commonly among those living in poverty. Genetic factors also play a role in susceptibility. The two main types of disease - paucibacillary and multibacillary - 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. The diagnosis is confirmed by finding acid-fast bacilli in a biopsy of the skin or by detecting the bacteria's DNA using polymerase chain reaction.

Leprosy is curable with multidrug therapy. Treatment of paucibacillary leprosy is with the medications dapsone, rifampicin, and clofazimine for six months. Treatment for multibacillary 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. At the end of 2016, there were 173,000 leprosy cases globally, down from some 5.2 million in the 1980s. The number of new cases in 2016 was 216,000. Most new cases occur in 16 countries, with India accounting for more than half. In the past 20 years, 16 million people worldwide have been cured of leprosy. About 200 cases are reported per year in the United States.

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. Separating people by placing them in leper colonies still occurs in places such as India, China, and Africa. However, most colonies have closed, since leprosy is not very contagious. Social stigma has been associated with leprosy for much of history, 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". It 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

The first noticeable sign of leprosy is often the development of pale or pinkish patches of skin that may be insensitive to temperature or pain. This is sometimes accompanied or preceded by nerve problems including numbness or tenderness in the hands or feet. Secondary infections, in turn, can result in tissue loss, causing fingers and toes to become shortened and deformed, as cartilage is absorbed into the body.

Approximately 30% of those affected experience nerve damage, and the nerve damage sustained is irreversible, even with treatment of the infection. Damage to nerves may cause sensation abnormalities, which may lead to infection, ulceration, and joint deformity.

Cause

M. leprae and M. 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 causative agents of 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.

An intracellular, acid-fast bacterium, M. leprae is aerobic and rod-shaped, and is surrounded by the waxy cell membrane coating characteristic of the genus Mycobacterium.

Due to extensive loss of genes necessary for independent growth, M. leprae and M. lepromatosis are obligate intracellular pathogens, and unculturable in the laboratory, a factor that leads to difficulty in definitively identifying the organism under a strict interpretation of Koch's postulates. The use of nonculture-based techniques such as molecular genetics has allowed for alternative establishment of causation. 

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 also has been reported in nonhuman primates, including the African chimpanzee, sooty mangabey, and cynomolgus macaque, as well as in 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, armadillos likely first acquired the organism incidentally from early American explorers. This incidental transmission was sustained in the armadillo population, and it is now transmitted back to humans, making leprosy a zoonotic disease.

Red squirrels (Sciurus vulgaris)—a threatened species—in England were found to have 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. Within Great Britain, widespread leprosy is found early in East Anglia, to which many of the squirrel furs were traded, and the strain is the same as that found in modern red squirrels on Brownsea Island. However, no squirrel cases have spread to a human for hundreds of years.

Risk factors

The greatest risk factor for developing leprosy is contact with another person infected by leprosy. Contacts of people with leprosy are five to eight 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.

Other risk factors are poorly understood. Conditions that reduce immune function, such as malnutrition, other illnesses, or host genetic differences, may increase the risk of developing leprosy. Infection with HIV does not appear to increase the risk of developing leprosy.

Transmission

Transmission of leprosy occurs during close contact with those who are infected. Transmission is proposed to be by nasal droplets, but many questions remain about its mode of transmission and epidemiology.

Leprosy is not known to be either sexually transmitted or highly infectious. People are generally no longer infectious after the first month of standard multidrug therapy.

Leprosy may also be transmitted to humans by armadillos, although the mechanism is not fully understood.

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.

The skin and the upper respiratory tract are the most likely entry route. While older research dealt with the skin route, recent research has increasingly favored the respiratory route. Experimental transmission of leprosy through aerosols containing M. leprae in immunosuppressed mice was accomplished, suggesting a similar possibility in humans.

Genetics

Several genes have been associated with a susceptibility to leprosy. Often, the immune system is able to eliminate leprosy during the early infection stage before severe symptoms develop. A defect in cell-mediated immunity may cause susceptibility to leprosy. 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 in some way at the biochemical level. Some evidence indicates not all people who are infected with M. leprae develop leprosy, and genetic factors have long been thought to play a role, due to the observation of clustering of leprosy around certain families, and the failure to understand why certain individuals develop lepromatous leprosy while others develop other types of leprosy.

Mechanism

How the infection produces the symptoms of the disease is not known.

Diagnosis

In countries where people are frequently infected, a person is considered to have leprosy if they have one these 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 sometimes reddish or copper-colored. The lesions may be macules (flat), papules (raised), or nodular. The sensory loss at the skin lesion is important because this feature can help differentiate it from other causes of skin lesions such as tinea versicolor. Thickened nerves are associated with leprosy and can be accompanied by loss of sensation or muscle weakness. However, without the characteristic skin lesion and sensory loss, muscle weakness 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 clinical.

In countries or areas where the disease 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, and the disability it causes.

Many kinds of leprosy are known, but some symptoms are common to them, including 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, and flat nose due to destruction of nasal cartilage. Also, phonation and resonation of sound occur during speech. Often, atrophy of the testes with resulting impotence occurs.

There is no recommended test to diagnose latent leprosy in asymptomatic contacts. However few people with latent leprosy went on to develop a positive test.

Classification

Several different approaches for classifying leprosy exist, but parallels exist.
  • The World Health Organization system distinguishes "paucibacillary" and "multibacillary" based upon the proliferation of bacteria.("pauci-" refers to a low quantity.)
  • The Ridley-Jopling scale provides five gradations.
  • The ICD-10, though developed by the WHO, uses Ridley-Jopling and not the WHO system. It also adds an indeterminate ("I") entry.
  • In MeSH, three groupings are used.
WHO Ridley-Jopling ICD-10 MeSH Description Lepromin test
Paucibacillary tuberculoid ("TT"),
borderline
tuberculoid ("BT")
A30.1, A30.2 Tuberculoid It is characterized by one or more hypopigmented skin macules and patches where skin sensations are lost because of damaged peripheral nerves that have been attacked by the human host's immune cells. Positive
Multibacillary midborderline
or
borderline ("BB")
A30.3 Borderline Borderline leprosy is of intermediate severity and is the most common form. Skin lesions resemble tuberculoid leprosy, but are more numerous and irregular; large patches may affect a whole limb, and peripheral nerve involvement with weakness and loss of sensation is common. This type is unstable and may become more like lepromatous leprosy or may undergo a reversal reaction, becoming more like the tuberculoid form.
Multibacillary borderline lepromatous ("BL"),
and lepromatous ("LL")
A30.4, A30.5 Lepromatous It is associated with symmetric skin lesions, nodules, plaques, thickened dermis, and frequent involvement of the nasal mucosa resulting in nasal congestion and nose bleeds, but, typically, detectable nerve damage is late. Loss of eyebrows and lashes can be seen in advanced disease. Negative

A difference in immune response to the tuberculoid and lepromatous forms is seen.

Leprosy may also be divided into:
This disease may also occur with only neural involvement, without skin lesions.

Prevention

Early detection of the disease is important, since physical and neurological damage may be irreversible even if cured. Medications can decrease the risk of those living with people with leprosy from acquiring the disease and likely those with whom people with leprosy come into contact outside the home. The WHO recommends that preventative medicine is given to people who are in close contact with someone who has leprosy. The suggested preventative treatment is a single dose of rifampicin (SDR) in adults and children over 2 years old who do not already have leprosy or tuberculosis. Preventative treatment is associated with a 57% reduction in infections within 2 years and a 30% reduction in infections within 6 years.

The Bacillus Calmette–Guérin (BCG) vaccine offers a variable amount of protection against leprosy in addition to its target of tuberculosis. It appears to be 26 to 41% effective (based on controlled trials) and about 60% effective based on observational studies with two doses possibly working better than one. The WHO concluded in 2018 that the BCG vaccine at birth reduces leprosy risk and is recommended in countries with high incidence of TB and leprosy. Development of a more effective vaccine is ongoing.

Treatment

MDT antileprosy drugs: standard regimens from 2010

Anti-leprosy medication

A number of leprostatic agents are available for treatment. A 3-drug regimen of rifampicin, dapsone and clofazimine is recommended for all people with leprosy, for 6 months for paucibacillary leprosy and 12 months for multibacillary leprosy.

Multidrug therapy (MDT) remains highly effective, and people are no longer infectious after the first monthly dose. It is safe and easy to use under field conditions due to its presentation in calendar blister packs. Post-treatment relapse rates remain low. Resistance has been reported in several countries, although the number of cases is small. A person with rifampicin-resistant leprosy should be treated with two second line drugs. Evidence on the potential benefits and harms of alternative regimens for drug-resistant leprosy is not yet available.

Skin changes

For people with nerve damage, protective footwear may help prevent ulcers and secondary infection. Canvas shoes may be better than PVC-boots. There may be no difference between double rocker shoes and below-knee plaster.

Topical ketanserin seems to have a better effect on ulcer healing than clioquinol cream or zinc paste, but the evidence for this is weak. Likewise, topical phenytoin has shown more efficacy than saline dressings.

Epidemiology

World distribution of leprosy, 2003
 
Disability-adjusted life year for leprosy per 100,000 inhabitants in 2004
  no data
  <1 .5="" span="">
  1.5–3
  3–4.5
  4.5–6
  6–7.5
  7.5–9
  9–10.5
  10.5–12
  12–13.5
  13.5–15
  15–20
  >20

In 2016, there were 216,108 new leprosy cases registered, corresponding to a global detection rate of 0.29 per 10,000 people. As of 2015, 14 countries reported contain 94% of new leprosy cases. India had the greatest number of new cases (60%), followed by Brazil (13%) and Indonesia (8%). Although the number of cases worldwide continues to fall, pockets of high prevalence remain in certain areas such as Brazil, South Asia (India, Nepal, Bhutan), some parts of Africa (Tanzania, Madagascar, Mozambique), and the western Pacific. About 150 to 250 cases are diagnosed in the United States each year. In the United States there are about 5,000 people who no longer have leprosy but have long-term complications of disease and continue to receive care.

In the 1960s, there were tens of millions of leprosy cases. A series of national (the International Federation of Anti-Leprosy Associations) and international (the WHO's "Global Strategy for Reducing Disease Burden Due to Leprosy") initiatives have reduced the total number and the number of new cases of the disease.

Disease burden

Although the number of new leprosy cases occurring each year is important as a measure of transmission, it is difficult to measure due to leprosy's long incubation period, delays in diagnosis after onset of the disease, and the lack of laboratory tools to detect it in the very early stages. Instead, the registered prevalence is used. Registered prevalence is a useful proxy indicator of the disease burden, as it reflects the number of active leprosy cases diagnosed with the disease and receiving treatment with MDT at a given point in time. The prevalence rate is defined as the number of cases registered for MDT treatment among the population in which the cases have occurred, again at a given point in time.

New case detection is another indicator of the disease that is usually reported by countries on an annual basis. It includes cases diagnosed with the onset of disease in the year in question (true incidence) and a large proportion of cases with onset in previous years (termed a backlog prevalence of undetected cases). 

Endemic countries also report the number of new cases with established disabilities at the time of detection, as an indicator of the backlog prevalence. Determination of the time of onset of the disease is, in general, unreliable, is very labor-intensive, and is seldom done in recording these statistics.

History

G. H. A. Hansen, discoverer of M. leprae
 
Using comparative genomics, in 2005, geneticists traced the origins and worldwide distribution of leprosy from East Africa or the Near East along human migration routes. They found four strains of M. leprae with specific regional locations. Strain 1 occurs predominantly in Asia, the Pacific region, and East Africa; strain 4, in West Africa and the Caribbean; strain 3 in Europe, North Africa, and the Americas; and strain 2 only in Ethiopia, Malawi, Nepal/north India, and New Caledonia

On the basis of this, they offer a map of the dissemination of leprosy in the world. This confirms the spread of the disease along the migration, colonisation, and slave trade routes taken from East Africa to India, West Africa to the New World, and from Africa into Europe and vice versa.

The oldest skeletal evidence for the disease date from 2000 BCE, as found in human remains from the archaeological sites of Balathal in India and Harappa in Pakistan.

Although retrospectively identifying descriptions of leprosy-like symptoms is difficult, what appears to be leprosy was discussed by Hippocrates in 460 BC. In 1846, Francis Adams produced The Seven Books of Paulus Aegineta which included a commentary on all medical and surgical knowledge and descriptions and remedies to do with leprosy from the Romans, Greeks, and Arabs.

Interpretations of the presence of leprosy have been made on the basis of descriptions in ancient Indian (Atharva Veda and Kausika Sutra), Greek, and Middle Eastern documentary sources that describe skin afflictions.

Leprosy probably did not exist in Greece or the Middle East before Common Era. It did not exist in the Americas before colonization by modern Europeans.

Skeletal remains from the second millennium BC, discovered in 2009, represent the oldest documented evidence for leprosy. Located at Balathal, in Rajasthan, northwest India, the discoverers suggest that if the disease did migrate from Africa to India, during the third millennium BC "at a time when there was substantial interaction among the Indus Civilization, Mesopotamia, and Egypt, there needs to be additional skeletal and molecular evidence of leprosy in India and Africa so as to confirm the African origin of the disease." A proven human case was verified by DNA taken from the shrouded remains of a man discovered in a tomb next to the Old City of Jerusalem dated by radiocarbon methods to 1–50 AD.

Distribution of leprosy around the world in 1891
 
However, a study published in 2018 found the oldest strains of leprosy in remains from Europe, the oldest strain being from Great Chesterford and dating back to 415 to 545 AD. These findings suggest a different path for the spread of leprosy where it may have originated in Western Eurasia. This study also indicates that there were more strains in Europe at the time than previously determined.

The causative agent of leprosy, M. leprae, was discovered by G. H. Armauer Hansen in Norway in 1873, making it the first bacterium to be identified as causing disease in humans.

The first effective treatment (promin) became available in the 1940s. In the 1950s, dapsone was introduced. The search for further effective antileprosy drugs led to the use of clofazimine and rifampicin in the 1960s and 1970s. Later, Indian scientist Shantaram Yawalkar and his colleagues formulated a combined therapy using rifampicin and dapsone, intended to mitigate bacterial resistance. Multi-drug therapy (MDT) combining all three drugs was first recommended by the WHO in 1981. These three antileprosy drugs are still used in the standard MDT regimens. 

Leprosy was once believed to be highly contagious and was treated with mercury—as was syphilis, which was first described in 1530. Many early cases thought to be leprosy could actually have been syphilis.

Resistance has developed to initial treatment. Until the introduction of MDT in the early 1980s, leprosy could not be diagnosed and treated successfully within the community.

Japan still has sanatoriums (although Japan's sanatoriums no longer have active leprosy cases, nor are survivors held in them by law).

The importance of the nasal mucosa in the transmission of M leprae was recognized as early as 1898 by Schäffer, in particular, that of the ulcerated mucosa.

Society and culture

Two lepers denied entrance to town, 14th century

The word "leprosy" comes from the greek word "λέπος (lépos) – skin" and "λεπερός (leperós) – scaly man.

India

British India enacted the Leprosy Act of 1898 which institutionalized those affected and segregated them by sex to prevent reproduction. The Act was difficult to enforce but was repealed in 1983 only after MDT therapy had become widely available. In 1983, the National Leprosy Elimination Programme, previously the National Leprosy Control Programme, changed its methods from surveillance to the treatment of people with leprosy. India still accounts for over half of the global disease burden.

Treatment cost

Between 1995 and 1999, the WHO, with the aid of the Nippon Foundation, supplied all endemic countries with free MDT in blister packs, channeled through ministries of health. This free provision was extended in 2000 and again in 2005, 2010 and 2015 with donations by the MDT manufacturer Novartis through the WHO. In the latest agreement signed between the company and the WHO in October 2015, the provision of free MDT by the WHO to all endemic countries will run until the end of 2020. At the national level, nongovernment organizations affiliated with the national program will continue to be provided with an appropriate free supply of this WHO-supplied MDT by the government.

Historical texts

Written accounts of leprosy date back thousands of years. Various skin diseases translated as leprosy appear in the ancient Indian text, the Atharava Veda, as early as 2000 BC. Another Indian text, the Manusmriti (1500 BC),  prohibited contact with those infected with the disease and made marriage to a person infected with leprosy punishable.

Biblically speaking, the Hebraic root tsara or tsaraath (צָרַע,—tsaw-rah'—to be struck with leprosy, to be leprous) and the Greek (λεπρός—lepros), are of broader classification than the more narrow use of the term related to Hansen's Disease. Any progressive skin disease (a whitening or splotchy bleaching of skin, raised manifestations of scales, scabs, infections, rashes, etc.…) as well as generalized molds and surface discoloration of any clothing, leather, and/or discoloration on walls surfaces throughout homes all came under the "law of leprosy" (Leviticus 14:54–57). Ancient sources also such as the Talmud (Sifra 63) make clear that tzaraath refers to various types of lesions or stains associated with ritual impurity and occurring on cloth, leather, or houses, as well as skin. It may sometimes be a symptom of the disease described in this article but has many other causes, as well. The New Testament describes instances of Jesus healing people with leprosy Luke 17:11, although the precise relationship between this, tzaraath, and Hansen's disease is not established.

The biblical perception that people with leprosy were unclean may be connected to a passage from Leviticus 13: 44–46, among others. Judeo–Christian belief, for some, held that leprosy was of moral consequence, and, as in many societies, early Christians believed that those affected by leprosy were being punished by God for sinful behavior. Moral associations have persisted throughout history. Pope Gregory the Great (540–604) and Isidor of Seville (560–636) considered people with the disease to be heretics.

Middle Ages

Medieval leper bell
 
It is believed that a rise in leprosy in Europe occurred in the Middle Ages based on the increased number of hospitals created to treat people with leprosy in the 12th and 13th centuries. France alone had nearly 2,000 leprosariums during this period. 

The social perception in medieval communities was generally one of fear, and those people infected with the disease were thought to be unclean, untrustworthy, and morally corrupt. People with leprosy were also often required to wear clothing that identified them as such or carry a bell announcing their presence. Segregation from mainstream society was common. The third Lateran Council of 1179 and a 1346 edict by King Edward expelled lepers from city limits. Because of the moral stigma of the disease, methods of treatment were both physical and spiritual, and leprosariums were established under the purview of the church.

19th century

Norway

Norway was the location of a progressive stance on leprosy tracking and treatment and played an influential role in European understanding of the disease. In 1832, Dr. JJ Hjort conducted the first leprosy survey, thus establishing a basis for epidemiological surveys. Subsequent surveys resulted in the establishment of a national leprosy registry to study the causes of leprosy and for tracking of the rate of infection. 

Early leprosy research throughout Europe was conducted by Norwegian scientists Daniel Cornelius Danielssen and Carl Wilhelm Boeck. Their work resulted in the establishment of the National Leprosy Research and Treatment Center. Danielssen and Boeck believed the cause of leprosy transmission was hereditary. This stance was influential in advocating for the isolation of those infected by sex to prevent reproduction.

Colonialism and imperialism

Father Damien on his deathbed in 1889
 
Though leprosy in Europe was again on the decline by the 1860s, Western countries embraced isolation treatment out of fear of the spread of disease from developing countries, minimal understanding of bacteriology, lack of diagnostic ability or knowledge of how contagious the disease was, and missionary activity. Growing imperialism and pressures of the industrial revolution resulted in a Western presence in countries where leprosy was endemic, namely the British presence in India. Isolation treatment methods were observed by Surgeon-Mayor Henry Vandyke Carter of the British Colony in India while visiting Norway, and these methods were applied in India with the financial and logistical assistance of religious missionaries. Colonial and religious influence and associated stigma continued to be a major factor in the treatment and public perception of leprosy in endemic developing countries until the mid-twentieth century.

Stigma

Despite effective treatment and education efforts, leprosy stigma continues to be problematic in developing countries where the disease is common. Leprosy is most common amongst impoverished or marginalized populations where social stigma is likely to be compounded by other social inequities. Fears of ostracism, loss of employment, or expulsion from family and society may contribute to a delayed diagnosis and treatment. 

Folk beliefs, lack of education, and religious connotations of the disease continue to influence social perceptions of those afflicted in many parts of the world. In Brazil, for example, folklore holds that leprosy is transmitted by dogs, it is a disease associated with sexual promiscuity, and is sometimes thought to be punishment for sins or moral transgressions. Socioeconomic factors also have a direct impact. Lower-class domestic workers who are often employed by those in a higher socioeconomic class may find their employment in jeopardy as physical manifestations of the disease become apparent. Skin discoloration and darker pigmentation resulting from the disease also have social repercussions.

In extreme cases in northern India, leprosy is equated with an "untouchable" status that "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."

Programs and treatment

The WHO states that diagnosis and treatment with MDT are easy and effective, and a 45% decline in disease burden has occurred since MDT has become more widely available. The organization emphasizes the importance of fully integrating leprosy treatment into public health services, effective diagnosis and treatment, and access to information.

In some instances in India, community-based rehabilitation is embraced by local governments and NGOs alike. Often, the identity cultivated by a community environment is preferable to reintegration, and models of self-management and collective agency independent of NGOs and government support have been desirable and successful.

Notable cases

Research directions

More research in ulcer prevention and treatment in leprosy is needed to better guide management of skin changes caused by leprosy-induced nerve damage.

Other animals

Wild nine-banded armadillos (Dayspus novemcinctus) in south central United States often carry Mycobacterium leprae. This is believed to be because armadillos have such a low body temperature. Leprosy lesions appear mainly in cooler body regions such as the skin and mucous membranes of the upper respiratory tract. Because of armadillos' armor, skin lesions are hard to see. Abrasions around the eyes, nose and feet are the most common signs. Infected armadillos make up a large reservoir of M. leprae and may be a source of infection for some humans in the United States or other locations in the armadillos' home range. In armadillo leprosy, lesions did not persist at the site of entry in animals, M. leprae multiplied in macrophages at the site of inoculation and lymph nodes.

Sex differences in intelligence

From Wikipedia, the free encyclopedia
 
Differences in human intelligence have long been a topic of debate among researchers and scholars. With the advent of the concept of g or general intelligence, many researchers have argued for no significant sex differences in g factor or general intelligence, while others have argued for greater intelligence for males, and others for females. These results depend on the methodology, tests researchers used for their claims, and the personal performances of the participants.
 
Some research indicates male advantages on some cognitive tests are minimized when controlling for socioeconomic factors. Other research has concluded that there is larger variability in male scores compared to female scores, which results in more males than females in the top and bottom of the IQ distribution. Additionally, there are differences in the capacity of males and females in performing certain tasks, such as rotation of objects in space, often categorized as spatial ability.

Historical perspectives

Prior to the 20th century, it was a commonly held view that men were intellectually superior to women. In 1801, Thomas Gisborne said that women were naturally suited to domestic work and not spheres suited to men such as politics, science, or business. He stated that this was because women did not possess the same level of rational thinking that men did and had naturally superior abilities in skills related to family support. 

In 1875, Herbert Spencer said that women were incapable of abstract thought and could not understand issues of justice and had only the ability to understand issues of care. In 1925, Sigmund Freud also stated that women were less morally developed in the concept of justice and, unlike men, were more influenced by feeling than rational thought. Early brain studies comparing mass and volumes between the sexes concluded that women were intellectually inferior because they have smaller and lighter brains. Many believed that the size difference caused women to be excitable, emotional, sensitive, and therefore not suited for political participation.

In the nineteenth century, whether men and women had equal intelligence was seen by many as a prerequisite for the granting of suffrage. Leta Hollingworth argued that women were not permitted to realize their full potential, as they were confined to the roles of child-rearing and housekeeping.

During the early twentieth century, the scientific consensus shifted to the view that gender plays no role in intelligence, but men consistently overestimated their IQs and women consistently underestimated their IQs.

In his 1916 study of children's IQs, psychologist Lewis Terman concluded that "the intelligence of girls, at least up to 14 years, does not differ materially from that of boys". He did, however, find "rather marked" differences on a minority of tests. For example, he found boys were "decidedly better" in arithmetical reasoning, while girls were "superior" at answering comprehension questions. He also proposed that discrimination, lack of opportunity, women's responsibilities in motherhood, or emotional factors may have accounted for the fact that few women had careers in intellectual fields.

Research on general intelligence

Background

Chamorro-Premuzic et al. stated, "The g factor, which is often used synonymously with general intelligence, is a latent variable which emerges in a factor analysis of various cognitive ('IQ') tests. They are not exactly the same thing. g is an indicator or measure of general intelligence; it's not general intelligence itself."

All or most of the major tests commonly used to measure intelligence have been constructed so that there are no overall score differences between males and females. Thus, there is little difference between the average IQ scores of men and women. Differences have been reported, however, in specific areas such as mathematics and verbal measures. Also, studies have found the variability of male scores is greater than that of female scores, resulting in more males than females in the top and bottom of the IQ distribution.

In favor of males or females in g factor

Research, using the Wechsler Adult Intelligence Scale (WAIS III and WAIS-R), that finds general intelligence in favor of males indicates a very small difference. This is consistent across countries. In the United States and Canada, the IQ points range from two to three points in favor of males, while the points rise to four points in favor of males in China and Japan. By contast, some research finds greater advantage for adult females. For children in the United States and the Netherlands, there are one to two IQ point differences in favor of boys. Other research has found a slight advatage for girls on the residual verbal factor.

A 2004 meta-analysis by Richard Lynn and Paul Irwing published in 2005 found that the mean IQ of men exceeded that of women by up to 5 points on the Raven's Progressive Matrices test. Lynn's findings were debated in a series of articles for Nature. He argued that there is a greater male advantage than most tests indicate, stating that because girls mature faster than boys, and that cognitive competence increases with physiological age, rather than with calender age, the male-female difference is small or negative prior to puberty, but males have an advantage after adolescence and this advantage continues into adulthood.

In favor of no sex differences or inconclusive consensus

Most studies find either a very small difference in favor of males or no sex difference with regard to general intelligence. In 2000, researchers Roberto Colom and Francisco J. Abad conducted a large study of 10,475 adults on five IQ tests taken from the Primary Mental Abilities and found negligible or no significant sex differences. The tests conducted were on vocabulary, spatial rotation, verbal fluency and inductive reasoning.

The literature on sex differences in intelligence having produced inconsistent results due to the type of testing used has resulted in debate among researchers. The issues remains unresolved if one uses standardized tests as Jensen (1998) and Colom, Garcia (2002) agrees that there might be a small insignificant sex difference in intelligence in general (IQ) but this may not necessarily reflect a sex difference in general intelligence or g factor. The difference between the two concepts is that IQ is a psychometric scoring system measured with standardized testing, while g factor is a latent scientific construct that correlates with all cognitive tests and achievements in life. Although most researchers distinguish between g and IQ, those that argue for greater male intelligence assert that IQ and g are synonymous (Lynn & Irwing 2004) and so the real division comes from defining IQ in relation to g factor. However, in 2008 Lynn and Irwing proposed that since working memory ability correlate highest with g factor, researchers would have no choice but to accept greater male intelligence if differences on working memory tasks are found. As a result, a neuroimaging study published by Schmidt (2009) conducted an investigation into this proposal by measuring sex differences on an n-back working memory task. The results found no sex difference in working memory capacity and thus contradicting the position pushed forward by Lynn and Irwing (2008) and more in line with those arguing for no sex differences in intelligence.

A 2012 review by researchers Richard E. Nisbett, Joshua Aronson, Clancy Blair, William Dickens, James Flynn, Diane F. Halpern and Eric Turkheimer discussed Arthur Jensen's 1998 studies on sex differences in intelligence. Jensen's tests were significantly g loaded but were not set-up to get rid of any sex differences (read differential item functioning). They summarized his conclusions as he quoted, "No evidence was found for sex differences in the mean level of g or in the variability of g. Males, on average, excel on some factors; females on others." Jensen's results that no overall sex differences existed for g has been reinforced by researchers who analyzed this issue with a battery of 42 mental ability tests and found no overall sex difference.

Although most of the tests showed no difference, there were some that did. For example, they found female subjects performed better on verbal abilities while males performed better on visuospatial abilities. For verbal fluency, females have been specifically found to perform slightly better in vocabulary and reading comprehension but significantly higher in speech production and essay writing. Males have been specifically found to perform better on spatial visualization, spatial perception, and mental rotation. Researchers had then recommended that general models such as fluid and crystallized intelligence be divided into verbal, perceptual and visuospatial domains of g; this is because, as this model is applied, females excel at verbal and perceptual tasks while males on visuospatial tasks, thus evening out the sex differences on IQ tests.

Variability

Some studies have identified the degree of IQ variance as a difference between males and females. Males tend to show greater variability on many traits; for example having both highest and lowest scores on tests of cognitive abilities.

Feingold (1992b) and Hedges and Nowell (1995) have reported that, despite average sex differences being small and relatively stable over time, test score variances of males were generally larger than those of females." Feingold "found that males were more variable than females on tests of quantitative reasoning, spatial visualisation, spelling, and general knowledge. ... Hedges and Nowell go one step further and demonstrate that, with the exception of performance on tests of reading comprehension, perceptual speed, and associative memory, more males than females were observed among high-scoring individuals."

Brain and intelligence

Differences in brain physiology between sexes do not necessarily relate to differences in intellect. Although men have larger brains, men and women typically achieve similar IQ results. For men, the gray matter volume in the frontal and parietal lobes correlates with IQ; for women, the gray matter volume in the frontal lobe and Broca's area (which is used in language processing) correlates with IQ.

Women have greater cortical thickness, cortical complexity and cortical surface area (controlling for body size) which compensates for smaller brain size. Meta-analysis and studies have found that brain size explains 6–12% of variance among individual intelligence and cortical thickness explains 5%.

Mathematics performance

Girl scouts compete in the USS California Science Experience at Naval Surface Warfare. In 2008, the National Science Foundation reported that, on average, girls perform as well as boys on standardized math tests, while boys are overrepresented on both ends of the spectrum.
 
A performance difference in mathematics on the SAT and international PISA exists in favor of males, though differences in mathematics course performance measures favor females. In 1983, Benbow concluded that the study showed a large sex difference by age 13 and that it was especially pronounced at the high end of the distribution. However, Gallagher and Kaufman criticized Benbow's and others' reports, which found that males were over-represented in the highest percentages, on the grounds that they had not ensured representative sampling.

In nearly every study on the subject, males have out-performed females on mathematics in high school, but the size of the male-female difference, across countries, is related to gender inequality in social roles. In a 2008 study paid for by the National Science Foundation in the United States, however, researchers stated that "girls perform as well as boys on standardized math tests. Although 20 years ago, high school boys performed better than girls in math, the researchers found that is no longer the case. The reason, they said, is simple: Girls used to take fewer advanced math courses than boys, but now they are taking just as many." However, the study indicated that, while boys and girls performed similarly on average, boys were over-represented among the very best performers as well as among the very worst.

A 2011 meta-analysis with 242 studies from 1990 to 2007 involving 1,286,350 people found no overall sex difference of performance in mathematics. The meta-analysis also found that although there were no overall differences, a small sex difference that favored males in complex problem solving is still present in high school.

With regard to gender inequality, some psychologists believe that many historical and current sex differences in mathematics performance may be related to boys' higher likelihood of receiving math encouragement than girls. Parents were, and sometimes still are, more likely to consider a son's mathematical achievement as being a natural skill while a daughter's mathematical achievement is more likely to be seen as something she studied hard for. This difference in attitude may contribute to girls and women being discouraged from further involvement in mathematics-related subjects and careers.

Stereotype threat has been shown to affect performance and confidence in mathematics of both males and females.

Spatial ability

Examples of figures from mental rotation tests.
 
A man playing a video game at the Japan Media Arts Festival. Spatial abilities can be affected by experiences such as playing video games, complicating research on sex differences in spatial abilities.
 
Metastudies show a male advantage in mental rotation and assessing horizontality and verticality and a female advantage in spatial memory. A proposed hypothesis is that men and women evolved different mental abilities to adapt to their different roles in society. This explanation suggests that men may have evolved greater spatial abilities as a result of certain behaviors, such as navigating during a hunt.

A number of studies have shown that women tend to rely more on visual information than men in a number of spatial tasks related to perceived orientation.

Results from studies conducted in the physical environment are not conclusive about sex differences, with various studies on the same task showing no differences. For example, there are studies that show no difference in finding one's way between two places.

Performance in mental rotation and similar spatial tasks is affected by gender expectations. For example, studies show that being told before the test that men typically perform better, or that the task is linked with jobs like aviation engineering typically associated with men versus jobs like fashion design typically associated with women, will negatively affect female performance on spatial rotation and positively influence it when subjects are told the opposite. Experiences such as playing video games also increase a person's mental rotation ability.

The possibility of testosterone and other androgens as a cause of sex differences in psychology has been a subject of study. Adult women who were exposed to unusually high levels of androgens in the womb due to congenital adrenal hyperplasia score significantly higher on tests of spatial ability. Some research has found positive correlations between testosterone levels in healthy males and measures of spatial ability. However, the relationship is complex.

Sex differences in academics

A 2014 meta-analysis of sex differences in scholastic achievement published in the journal of Psychological Bulletin found females outperformed males in teacher-assigned school marks throughout elementary, junior/middle, high school and at both undergraduate and graduate university level. The meta-analysis, done by researchers Daniel Voyer and Susan D. Voyer from the University of New Brunswick, drew from 97 years of 502 effect sizes and 369 samples stemming from the year 1914 to 2011.

Beyond sex differences in academic ability, recent research has also been focusing on women's underrepresentation in higher education, especially in the fields of natural science, technology, engineering and mathematics (STEM).

Green development

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