Evidence for subduction-related metamorphism on the coast of Scotland during the Mesoarchean-to-Neoarchean transition.

Plate tectonics are a fundamental part of the Earth's geological system, providing a means by which the planet is able to shed heat from its interior. Under this system crustal deformation and magmatism are generally confined to the margins of the lithospheric plates, with the otherwise stiff plates are weakened, softened, and recycled into the the Earth's mantle along subduction zones, while new crustal material is formed at seafloor spreading zones. As far as we know, plate tectonics are only found on Earth, which has led to speculation that the process may have been essential for the creation of conditions for life, or at least complex life. As such when and how the plate tectonics came about is of great interest to scientists. 

Potential dates for the origin of plate tectonics range from the Hadean Eon, more than four billion years ago, to the early Neoproterozoic, less than one billion years ago. However, finding evidence to support such hypotheses has proven difficult. The ideal geological evidence for plate tectonics would be metamorphic structures such as eclogites (associated with the shallow subduction of oceanic crust) or blueschists (associated with the deep subduction of crustal material) formed under a low temperature/pressure (thermobaric) regime, ideally less than 375 °C/GPa (apparently similar rocks formed under higher tthermobaric regimes are presumed to have formed due to different conditions). The oldest known ecglogites are found in Cameroon and the Democratic Republic of Congo, and are about 2.1 billion years old, while the oldest known blueschists are found in China, and are only 750-800 million years old.

Thus if plate tectonics was occurring during the Archaean (between 4 and 2.5 billion years ago), then there is a surprising lack of evidence for it.

In a paper published in the journal Geology on 1 January 2026, Meiyun Huang of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, and the College of Earth and Planetary Sciences at the University of the Chinese Academy of Sciences, Shujuan Jiao, also of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, Tim Johnson, Chris Clark, and Jie Yu, of the Curtin Frontiers Institute for Geoscience Solutions at Curtin University, Guangyu Huang, again of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, and Jinghui Guo, once again of the State Key Laboratory of Lithospheric and Environmental Coevolution at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, and the College of Earth and Planetary Sciences at the University of the Chinese Academy of Sciences, present of a study of a section of the Lewisian Gneiss Complex on the northwest coast of Scotland, which they date to about 2.8 billion years ago, and which they suggest was formed under temperature and pressure conditions consistent with a subductive plate margin setting.

Gneisses are course-grained metamorphic rocks which show distinct banding, but which do not tend to cleave along those bands. They typically form at temperatures in excess of 300°C and pressures of between 0.2 and 1.5 GPa, and can be derived from both igneous and sedimentary source rocks. The Lewisian Gneiss Complex is a grey gneiss terrane which has yielded magmatic ages of between 3.1 and 2.8 billion years. This includes layers of ultramafic–mafic rock interlayered with a layered garnet-biotite rock known as the brown gneiss, which is thought to have originally been of sedimentary or volcanosedimentary origin.

Rocks from the Lewisian Gneiss Complex on the Scottish mainland have previously been shown to date from the Neoarchean (2.8-2.5 billion years ago) and to have been formed at temperatures in excess of 900°C, although the pressure at which these rocks formed has been harder to determine, with estimates for peak pressure ranging from about 0.8 GPa to more than 1.5 GPa. There are also two proposed interpretations on the timeline over which these rocks formed, with one proposing two distinct metamorphic episodes, one between 2.8 and 2.7 billion years ago, and the other at about 2.5 billion years ago, and the other proposing a single extended metamorphic event lasting about 200 million years. 

(A) Simplified geological map of the Lewisian Gneiss Complex in northwest Scotland. Inset shows location of the Complex. (B) Geological map of the Scourie area in the Assynt terrane showing the location of the studied sample. (C) Outcrop of the studied sample (SC18-02; migmatitic aluminosilicate-bearing metasedimentary rock; 58°21′45″N, 5°09′49″W). Huang et al. (2026).

One possible interpretation is that the Garnet-rich fragments found within the ultramafic–mafic bodies represent retrogressed eclogites (metamorphic rocks which have recrystallised into their current form in response to the lowering of the temperature and pressure from the conditions in which they originally formed) which may have been heated to temperatures as high as 1040–1060°C and exposed to pressures as high as 2.2-2.4 GPa around 2.5 billion years ago, which would imply deep subduction during the late Neoarchaean. An alternative possibility is that they represent xenoliths, fragments of pre-existing rock which became incorporated into  surrounding rock during the emplacement of a volcanic basalt or gabro.

Huang et al. analysed samples taken from a migmatitic aluminosilicate-bearing metasedimentary rock within the Lewisian Gneiss Complex, looking at the mineral phases formed by oxides of sodium, calcium, potassium, iron, magnesium, aluminium, silicon and titanium, all of which from different minerals under different temperature and pressure conditions, as well as examining the whole rock composition, occurrence of zirconium within the mineral rutile (which is temperature dependent), and the silica content of the mineral phengite, which is dependent on the pressure at which it formed.

The specimen is a migmatic 'brown gneiss' comprising brown layers rich in garnet and biotite, and white layers which are composed largely of feldspar. Examined in thin section, the material is about 50% plagioclase by volume, with about 18% garnet, 10% biotite, 10% alumminosilicates, 8% potassium feldspar, and small amounts of corundum, spinel, white mica, zircon, rutile, ilmenite, and pyrite.

(A) Distribution of minerals in the sample SC18-02 from the Lewisian Gneiss Complex in northwest Scotland. Alm, almandine; Pyr, pyrope. (B) Detailed Tescan Integrated Mineral Analyzer image showing mineral inclusions in garnet. Rt, rutile; Py, pyrite; Ky, kyanite; Phn, phengite; Crn, corundum; Spl, spinel. (C) Phengite, rutile, and kyanite inclusions within garnet (Grt). (D) Quartz and kyanite inclusions in garnet cores. (E) Spinel, corundum, and kyanite surrounded by biotite (Bt) in garnet. (F) Kyanite, pyrite, and biotite in the garnet. Pl, plagioclase. (G) Kyanite inclusions in garnet cores and sillimanite (Sil) inclusions in garnet rims. (H) An inclusion in corundum showing rutile replaced by ilmenite (Ilm). Huang et al. (2026).

Garnet grains within the sample were up to 12 mm in diameter, and rich in inclusions, including isolated and polymineralic spinel, white mica, corundum, rutile, ilmenite, plagioclase, potassium-feldspar, quartz, biotite, and/or aluminosilicate. White mica, which was largely confined to inclusions within garnet, had a high silicon content, with most grains being classifiable as phengite (high silicone mica). Kyanite occured as isolated inclusions or together with corundum, rutile, spinel, and/or biotite in poly￾mineralic inclusions concentrated within garnet cores. Sillimanite was found in both the rims of garnets and the surrounding matrix, with no preferential orientation. Rare quartz grains were found within the cores of garnets, although they were otherwise largely absent. Corundum primarily occurs in the matrix in contact with sillimanite, spinel, and rutile, where it is commonly replaced at its margins by biotite, and rarely as polymineralic inclusions with spinel and kyanite within garnet. Rutile is present both as inclusions and within the matrix.Rarely, rutile inclusions are partially replaced by ilmenite.

Biotite found as inclusions within garnets has a different composition from biotite within the surrounding matrix, containing a lower proportion of both magnesium and titanium oxide. Spinel grains within the matrix contain slightly more zinc than those within garnet inclusions. Within garnet grains, these spinel inclusions tend to be associated with kyanite and corundum, and many are partially replaced by biotite. Spinel grains in the matrix are typically in contact with corundum and are commonly surrounded by sillimanite or biotite. However, the high zinc content of these spinel grains makes it hard to assess the temperature and pressure under which they formed, so they were excluded from the remainder of the study.

The presence of isolated inclusions of phengite, kyanite, rutile, quartz, and polymineralic inclusions including corundum, spinel, kyanite, rutile, phengite, and/or biotite within garnets is considered by Huang et al. as indicative of two phases of high-pressure metamorphism, with minerals formed by the first phase partially overwritten by the second. The presence of inclusions of sillimanite and plagioclase within the rims of garnet grains, as well as within the matrix assemblage, are taken as evidence for two later phases of high temperature metamorphism.

In order to determine the temperature and pressure conditions during the first phase of metamorphism, Huang et al. attempted to develop a phase equilibrium model for the whole rock. The presence of phengite, kyanite, and rutile within a quartz matrix suggests high pressure/low temperature conditions, with the silicon content of the phengites suggesting a pressure in excess of 2.4 GPa. Huang et al. estimate that during this first phase, temperatures reached 580-660°C and pressures between 1.5 and 2.5 GPa, giving a thermobaric ratio of between 230 °C/GPa (580 °C/2.5 GPa) and 440 °C/GPa (660 °C/1.5 GPa).

A second phase is deduced from the presence of an association of the minerals corundum, kyanite, biotite, plagioclase, and rutile/ilmenite. This association can only form at temperatures of between 830 and 880°C and pressures of between 1.1 and 1.7 GPa, consistent with the temperature deduced from the concentration of zirconium in rutile, approximately 740–960°C. This would correspond to a thermobaric ratio of between 490°C/GPa (830°C/1.7 GPa) and 800°C/GPa (880°C/1.1 GPa).

Another association present, comprising corundum, mesoperthite/antiperthite, and rutile, suggests a phase with higher temperatures but lower pressure. This association probably formed at a temperature of between 880 and 1000°C, but at a pressure of only 0.9.1.4 GPa. This is corroborated by zirconium-in-rutile data for this association, which suggests a formation temperature of about 800 to 1000°C. This would correspond to a thermobaric ratio of between 630°C/GPa (880°C/1.4 GPa) and 1110°C/GPa (1000°C/0.9 GPa). 

Huang et al. were able to obtain a lutetium–hafnium from a garnet within the sample associated with the high pressure phase of 2.81 billion years (the  isotope lutetium¹⁷⁶ decays to hafnium¹⁷⁶ at a predictable rate, with a half life of 37.1 billion years, enabling this system to be used for dating minerals which would not have contained hafnium at their time of formation).

Previous studies of the Lewisian Gneiss Complex have suggested formation under high pressure conditions, but not a precise age for the rocks nor any insight into the pressure-temperature relationship under which it formed. Huang et al. identify a low temperature/pressure event at about 2.8 billion years ago, associated with the formation of phengite, rutile, kyanite, and quartz inclusions within garnet. During this phase, temperatures reached 580–660°C and pressures reached 1.5–2.5 GPa, corresponding to thermobaric ratios of 230–440°C/GPa. This is consistent with the conditions associated with recent subductive margins where rock metamorphism occurs, but lower than is typical for Archean metamorphic terranes, which generally have thermobaric ratios of over 500°C/GPa.

A second phase is identified based upon the kyanite, biotite, and corundum inclusion complex, thought to have formed under conditions where the pressure had fallen by about 0.7 GPa, but the temperature had risen by about 200°C. This is consistent with the orogenic relaxation stage of a collisional cycle, where the horizontal movement of one plate into another has caused an episode of uplift, but that this horizontal movement has now stopped, causing the pressure within the rocks to slowly relax. This differs from the predominant system within Archean metamorphic environments, where the temperatures and pressures appear to have continued to climb, reaching levels far higher than seen in recent settings.

The low thermobaric ratios reported by Huang et al. are the lowest recorded for any Archean setting, and the only known example of low temperature/pressure metamorphism from the Archean. They propose the rocks or the Lewisian Gneiss Complex may preserve a record of a transition from a pre-plate tectonic regime to one in which subduction is beginning to occur, in a process that would eventually develop into plate tectonics. It has previously been suggested that this transition may have occurred during the Mesoarchean (between about 3.2 and 2.8 billion years ago) on the margins of the North Atlantic craton, as a result of the thickening and strengthening of the lithosphere, and long-term cooling of the mantle.

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Two dead in Meningitis outbreak in Kent, southern England.

Two people have died in an outbreak of Meningitis in the city of Canterbury, in Kent, southern England, this week, according to the UK Health Security Agency. Both of those who have died have been described as having been teenage students studying at the University of Kent. A further eighteen cases of the disease have been confirmed, sixteen of whom live in or close to Canterbury, with one patient each in London and Paris, both of whom are known to have visited Canterbury immediately before becoming unwell. A further eleven possible cases are under investigation. 

The location of the University of Kent. Google Maps.

Meningitis is a serious infection of the meninges, the membranes covering the brain and spinal cord. Several different Bacteria can cause Meningitis, however, Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis (sometimes spelled Neisseria meningitis) are the most common, and are transmitted from person to person through droplets of respiratory or throat secretions from infected people.

The average incubation period for Meningococcal Meningitis is 4 days, but can range between 2 and 10 days. The most common symptoms of Meningitis are a stiff neck, high fever, sensitivity to light, confusion, headaches and vomiting. Even with early diagnosis and adequate treatment, 5% to 10% of patients die, typically within 24 to 48 hours after the onset of symptoms. Bacterial Meningitis may result in brain damage, hearing loss or a learning disability in 10% to 20% of survivors. A less common, but even more severe (and often fatal), form of Meningococcal Disease is Meningococcal Septicaemia, which is characterised by a haemorrhagic rash and rapid circulatory collapse.

The Canterbury outbreak has been linked to the B serotype of Neisseria meningitidis, a form of Betaproteobacterium. A serotype is a distinct population within a species of Bacteria or Virus which presents different antigen proteins on the surface of its cells, and therefore requires the body to develop a different antibody response. A total of 12 serotypes of Neisseria meningitides have been identified, six of which (A, B, C, W, X and Y) can cause Meningococcal Meningitis epidemics.

Two serotypes 1a and 1b with antigens 2a and 2b on surface. Corresponding antibodys 3a and 3b with the possibility to bind to the antigens. Anna Bauer/Wikimedia Commons.

In the UK, a vaccine for Neisseria meningitidis serotypes A, C, W, & Y is typically offered to school pupils aged 14-15, while a vaccine for serotype B, which is particularly associated with outbreaks in infants, is offered to babies. However, this latter vaccination was only introduced in 2015, and therefore most people over the age of 15 in the UK are not vaccinated against this strain. The charity Meningitis Now, which campaigns on issues relating to the disease in the UK, as well as offering advise to those affected by or concerned about Meningitis, has been campaigning for a roll-out of the serotype B vaccine to older groups. 

As a response to the current outbreak, the University of Kent has arranged for a vaccination program for students to be set up on its campus, where antibiotics, which can help to fight the disease, are also available. Advice for staff and students at the university can be found here. Other people who are concerned that they may have been exposed should contact their GP (a GP, or General Practitioner, is a family doctor in the UK), or the National Health Service's NHS111 help service.

Students at the University of Kent in Canterbury queuing to get Meningitis B vaccine. PA Media.

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Meteorite fragments recovered in Germany after fireball seen over northwestern Europe.

More than 3000 witnesses in Belgium, France, Germany, Luxembourg, and the Netherlands have reported observing a bright fireball meteor at about 6.55 pm local time (about 5.55 pm GMT) on Sunday 8 March 2026, with some witnesses also reporting a sonic boom. The meteor is described as having moved from southwest to northeast for about six seconds before exploding in a fireball over the German state of Rhineland-Palatinate. A fireball is defined as a meteor (shooting star) brighter than the planet Venus. 

A very bright fireball moving from the southwest to the northeast was observed by many people in Belgium, France, Germany, Luxembourg, and the Netherlands. Bernd Klemt/AllSky7 fireball network/European Space Agency.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as a luminous object. However, this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).

These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.

Shortly after the meteor was sighted, two residents of a flat in the German city of Koblenz reported an impact which had caused a football-sized hole in their roof, as well as damage to a tiled floor in the room underneath. A search of the flat yielded eleven fragments of rock with masses of between 6 and 161 g. A number of smaller fragments were subsequently found in a neighbouring courtyard by professional meteorite-hunters and sold. Police in Koblenz have subsequently issued a warning to other meteorite-hunters in the area to respect private property, and not to collect suspected fragments from areas which they have not been given permission to enter.

The largest of the meteorite fragments recovered from a home in Koblenz, Germany, weighing 161 g. SWR.

The meteorite fragments have a pale interior and a near-black crust, making it likely that they are a type of stoney meteorite called a HED (howardite–eucrite–diogenite) achondrite breccia. These meteorites resemble terrestrial igneous rocks, and are therefore presumed to have come from a body large enough for magma differentiation and igneous processing to have occurred. HED meteorites comprise about 5% of all meteorites recovered on Earth, and about 60% of achondritic meteorites (meteorites which do not contain chondrules, spherules of glassy material thought to have formed from molten droplets in space before being incorporated into larger bodies).

Fragments of probable HED meteorite recovered from a flat in Koblenz, Germany. SWR.

While HED meteorites vary somewhat in composition, all are thought to derive from the surface of the Asteroid 4 Vesta. Studies of these meteorites have produced crystallisation ages of between 4.43 and 4.55 billion years, and all show signs of having formed in an environment where igneous differentiation has occurred. These meteorites are thought to have been dislodged from the surface of their parent body by ancient impacts.

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Asteroid 2026 EM passes the Earth.

Asteroid 2026 EM passed by the Earth at a distance of about 28 424 km (7% of the average distance between the Earth and the Moon, or 0.02% of the distance between the Earth and the Sun, but 71 times the distance at which the International Space Station orbits the Earth), at about 7.45 pm GMT on Monday 7 March 2026. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. Asteroid 2026 EM has an estimated equivalent diameter of 1-3 m (i.e. it is estimated that a spherical object with the same volume would be 1-3 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) more than 42 km above the ground, with only fragmentary material (if that) reaching the Earth's surface.

The relative positions of 2026 EM, the Earth, and the Moon at 8.00 pm on Monday 7 March 2026. JPL Small Body Database.

2026 EM was discovered on 6 March 2026 (the day of its closest approach to the Earth) by the University of Szeged's Szeged Asteroid Program, which is located at the Piszkéstető Mountain Station in the Mátra Mountains to the northeast of Budapest. The designation 2022 EM implies that it was the 12th asteroid (object M - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 25, with a number added to the end each time the alphabet is ended so that A = 1, A1 = 26, A2 = 51, etc., which means that M implies the 12th asteroid) discovered in the first half of March 2026 (period 2026 E - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

The relative positions of 2026 EM, the Earth, and the planets of the Inner Solar System at 8.00 pm on Monday 7 March 2026. JPL Small Body Database.

2026 EM has a 425 day (1.16 year) orbital period, with an elliptical orbit tilted at an angle of 4.77° to the plain of the Solar System which takes in to 0.89 AU from the Sun (89% of the distance at which the Earth orbits the Sun) and out to 1.32 AU (132% of the distance at which the Earth orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that Asteroid 2026 EM has occasional close encounters with the Earth, with the most recent having happened in March 2019, and the next predicted for March 2039. The asteroid also has occasional close encounters with the planet Mars, with the next such encounter predicted for May 2032.

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Chile officially recognised as the first country in the Americas to have eliminated Leprosy.

Chile has become the first country in the Americas to be recognised to have officially eliminated Leprosy, according to a press release issued by the World Health Organization on 4 March 2024. Chile is only the second country globally to reach this goal, following Jordan in September 2024. The conformation also makes Chile the sixth country in the Americas to have eliminated at least one Neglected Tropical Disease, joining Brazil, Colombia, Ecuador, Guatemala, and Mexico.

Chilean flags. Mark Scott Johnson/Wikimedia Commons.

Leprosy was first recorded in Chile on Rapa Nui (Easter Island) in the late nineteenth century, with some subsequent cases reported on the mainland. The last reported case of a person becoming infected with the disease on Chilean territory occurred on Rapa Nui in 1993. However, the country has continued widespread monitoring for Leprosy, with 47 cases reported between 2012 and 2023, all of which were acquired outside of the country, and all of which were successfully treated.

Leprosy is caused by the Bacteria Mycobacterium leprae and Mycobacterium lepromatosis. It is essentially a skin disease, with the Bacteria infecting patches of skin, which can become dry and itchy, lose their pigmentation, suffer skin thickening, nerve damage, and local immune system failure, which can cause the patches vulnerable to secondary infections by other Bacteria, Fungi, and Viruses. It is these secondary infections which cause the ulceration and tissue loss associated with the disease, which can lead to shortening or loss of fingers and toes, or even facial features. The nerve damage associated with the disease can cause patients to fail to notice wounds, making them more vulnerable to infection.

Mycobacterium leprae heavy load (6+) in Ziehl-Neelsen stained slit skin smear microscopy at a magnification of 2000X. Ajay Kumar Chaurasiya/Wikimedia Commons.

Leprosy is thought to be spread by mucus droplets exposed by through the mouth or nose (which can enable it to spread among children rapidly) but not through most other forms of contact; it is not sexually transmitted, and patients with HIV do not appear to be any more vulnerable, although malnutrition may be a factor. Much of the Human population appear to be naturally immune to Leprosy, with vulnerability to the disease being genetic, and tending to run in families, which can be problematic, particularly in poorer communities where people are living in cramped conditions and have trouble accessing medicine. 

Leprosy is a zoonotic disease, with wild reserves of the Bacteria found in a number of Animal species, including Primates such as the Chimpanzee, the Sooty Mangabey, and the Cynomolgus Macaque. In Europe is thought to have been spread by Red Squirrels, which are known to be vulnerable to the disease, and which were extensively hunted for their fur in the Middle Ages. The disease is thought to have been introduced to the Americas by European settlers, but has become established in there in Armadillos, which can act as a wild vector, spreading Leprosy back to Humans.

The first effective treatment for Leprosy was developed by Alice Augusta Ball, a young researcher at the College of Hawai'i (now the University of Hawai'i), in 1915 (Ball is also noted to have been the first African American woman to achieve a masters degree in chemistry, the first African American woman hired as a chemistry instructor at the College of Hawai'i, and possibly the first African American woman to publish an article in a major scientific journal). Today it is typically treated with a combination of antibiotics such as rifampicin, dapsone, and clofazimine, with other antibiotics available if resistance to these is encountered. Such treatments can typically eliminate the disease completely, although the courses of treatment are long (6-12 months) and involves taking multiple pills each day, which can be problematic, particularly in younger children.

Alice Augusta Ball in 1915. University of Hawai'i/Wikimedia Commons.

Leprosy is still considered to be endemic to 132 countries, with around 200 000 new cases reported each year. The worst affected countries are Brazil, India, and Indonesia, each of which typically reports more than 10 000 new cases each year. Twelve other countries, Bangladesh, Democratic Republic of the Congo, Ethiopia, Madagascar, Mozambique, Myanmar, Nepal, Nigeria, Philippines, Somalia, Sri Lanka and Tanzania, typically report between 1000  and 10 000 new cases per year, while another 117 countries typically report between 1 and 1000 cases per year. The World Health Organization is currently working towards the global elimination of Leprosy in partnership with the Swiss drug company Novartis, which provides multi-drug therapy for the disease to patients anywhere in the world at no cost, under the Partnership to Eliminate Leprosy scheme.

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