Tuesday 27 April 2021

Two Earthquakes in Moyen-Ogooué Province, Gabon.

The United States Geological Survey recorded two Earthquakes in Moyen-Ogooué Province, Gabon, on Tuesday 27 April 2021. The first, a Magnitude 4.5 Earthquake at a depth of 10 km, occurred roughly 44 km to the southwest of the town of Lambaréné, about 2 minutes before  1.40 am local time (about two minutes before 0.40 am GMT), with the second, a Magnitude 4.7 Earthquake also at a depth of 40 km, which happened about 40 km to the southwest of Lambaréné, happening about two minutes later. There are no reports of any damage or injuries associated with these events, but they are likely to have been felt locally.

The approximate locations of the 27 April 2021 Gabon Earthquakes. USGS.

Earthquakes are extremely rare in Gabon, which lies over Precambrian basement rocks which for the most part have not been tectonically active since the rifting which separated Africa from South America as the Atlantic Ocean in the Mesozoic. However, the North Gabon Sub-basin is cross-cut by a series of northwest-southeast trending faults associated with this Mesozoic rifting. Movement on these rift zones is now extremely limited, but the area is overlain by extensive evaporite salt deposits, which are structurally weak, and altering the way in which faults propagate.

Fault systems and tectonic units division of the Gabon Coastal Basin. Fz. Fault. Chen et al. (2013).

Because salt deposits are dense and structurally weak, movement on faults below them does not typically propagate upwards though them. Instead, the salt layer will often expand laterally, accommodating the movement of the fault. Eventually, however, this displacement becomes to great for the overburden layer, which leads to the development of new faults in that layer, offset from the faults in the basement. Thus, gradual movements in the basement rock can be translated into sudden, shallow faulting in surface layers, which we experience as Earthquakes.

Fault development on a salt layer. Wikipedia.

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Saturday 24 April 2021

World Health Organisation confirms The Gambia has eliminated Trachoma as a public health problem.

The World Health Organization has validated The Gambia for having eliminated Trachoma as a public health problem, making it the second country in the World Health Organisation’s African Region to achieve this milestone, according to a press release issued on 20 April 2021. 'This is a great step towards the 2030 goals set by the recently launched 2021–2030 road map for neglected tropical diseases,' said Ren Minghui, the World Health Organisation’s Assistant Director-General for Universal Health Coverage/Communicable and Noncommunicable Diseases. 'Gambia has become the second country this year, after Côte d’Ivoire, to eliminate a neglected tropical disease.'

A Gambian mother getting checked for Trachoma. Trachoma is a neglected tropical eye disease. Infection mainly affects children, becoming less common with increasing age. Gambia Eye Health Programm/World Health Organisation.

The Gambia’s success in eliminating Trachoma is largely attributed to strong collaboration with partner organisations to implement the World Health Organisation’s SAFE strategy. 'This is a remarkable achievement that has saved children, mothers and families from preventable visual impairment or blindness, and improved their quality of life and well-being,' said Matshidiso Moeti, the World Health Organisation’s Regional Director for Africa. 'It is also a clear sign that we can achieve significant milestones through dedicated efforts in tackling health challenges in the region.'

At the heart of the efforts against trachoma are Gambian community volunteers, who have played a crucial role in mobilizing communities and promoting behaviour change.

A 2018–2019 survey on Trachomatous Trichiasis (the advanced, blinding stage of trachoma) in Gambia found that the prevalence of this condition among people aged 15 years and above ranged from 0% to 0.02%, well under the threshold required for elimination of Trachoma as a public health problem. This is a huge achievement compared to the mid-1980s, when a national survey estimated that Trachoma was responsible for almost 1 out of 5 cases of blindness, countrywide.

Trachoma is a neglected tropical eye disease. Infection mainly affects children, becoming less common with increasing age. The long-term consequences of infection develop years or even decades later. In adults, women are up to 4 times more likely than men to be affected by the blinding complications of Trachoma, mainly due to their close contact with infected children.

The Gambia and the World Health Organisation will continue to closely monitor previously endemic populations to ensure there is a rapid, proportionate response to any resurgence of the disease. 

Despite The Gambia’s success, Trachoma remains endemic in 27 countries in the World Health Organisation’s African Region, and 29 countries on the African continent overall. Progress against neglected tropical diseases has alleviated the Human and economic burden they impose on the world’s most disadvantaged communities. The 2021–2030 road map for neglected tropical diseases seeks to prevent, control, eliminate or eradicate 20 diseases by 2030.

Globally, Trachoma remains a public health problem in 45 countries, with an estimated 137 million people living in areas endemic for the disease. Significant progress has been made over the past few years, the number of people requiring antibiotic treatment for Trachoma elimination in the African Region fell by 72 million from 189 million in 2014 to 117 million in 2020.

Trachoma is a devastating eye disease caused by infection with the Bacterium Chlamydia trachomatis. The infection spreads from person to person through contaminated fingers, fomites and flies that have come into contact with discharge from the eyes or nose of an infected person.

Environmental risk factors for Trachoma transmission include poor hygiene, overcrowded households, inadequate access to water, and inadequate access to, or use of, proper sanitation facilities.

Repeated infections in childhood lead to scarring of the inner side of the upper eyelids, resulting in inward turning of the eyelid margin, with the lashes touching the globe. This is a painful condition known as Trachomatous Trichiasis, if left untreated, this condition can result in visual impairment and blindness.

In 1996, the World Health Organisation launched the WHO Alliance for the Global Elimination of Trachoma by 2020. With other partners in the Alliance, the World Health Organisation supports country implementation of the SAFE strategy and the strengthening of national capacity through epidemiological assessment, monitoring, surveillance, project evaluation and resource mobilisation.

Elimination of Trachoma is inexpensive, simple and extremely cost-effective, yielding a high rate of net economic return.

Chlamydia trachomatis is a member of the Chlamydiae, a diverse group of Bacteria which are generally pathogenic. Most well understood members of Chlamydiae are intracellular parasites of Animals and single-celled Eukaryotes, and it has long been presumed that these Bacteria were obligate parasites, incapable of living or reproducing outside of Eukarotic cells. However, some free-living species have recently been discovered in deep marine environments, although little is yet known about the life-cycle of these Bacteria.

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Asteroid 2021 HN passes the Earth.

Asteroid 2021 HN passed by the Earth at a distance of about 254 200 km (0.66 times the average distance between the Earth and the Moon, or 0.17% of the distance between the Earth and the Sun), slightly before 7.55 am GMT on Monday 19 April 2021. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2021 HN has an estimated equivalent diameter of 8-25 m (i.e. it is estimated that a spherical object with the same volume would be 8-25 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) betwenn 35 and 18 km above the ground, with only fragmentary material reaching the Earth's surface.


Asteroid 2021 HN imaged on 17 April 2021 from London, England. Image is a single three minute exposure. Asteroid is the point indicated by the red lines, which has moved only slightly over the course of the image gathering, while the longer lines are stars that have moved considerably in the same time. Northolt Branch Observatories/Twitter.

2021 HN was discovered on 17 April 2021 (twi days before its closest approach to the Earth) by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2021 HN implies that the asteroid was the 13th object (asteroid Z - in numbering asteroids the letters A-Z, 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 N = 13) discovered in the second half of April 2021 (period 2021 H - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

The relative positions of 2021 HN and the Earth on 9 March 2021. JPL Small Body Database.

2021 HN has a 1157 day (3.17 year) orbital period, with an elliptical orbit tilted at an angle of 16.0° to the plain of the Solar System which takes in to 0.79 AU from the Sun (79% of the distance at which the Earth orbits the Sun) and out to 3.52 AU (352% of the distance at which the Earth orbits the Sun, and motre than the distance at which the planet Mars 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 2021 HN has occasional close encounters with the Earth, with the last thought to have happened in September 1932 and the next predicted in September 2024. 2021 HN also has occasional close encounters with the planet Jupiter, which it last came close to in April 2013.

The orbit and current position of 2021 HN. The Sky Live 3D Solar System Simulator.

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