Tuesday, 19 May 2020

Outbreaks of pandemics.

Black Death 1720
The Black Death, also known as the Pestilence and the Plague, was the most fatal pandemic recorded in human history, resulting in the deaths of up to 75–200 million people in Eurasia and North Africa, peaking in Europe from 1347 to 1351. Plague, the disease caused by the bacterium Yersinia pestis, was the cause; Y. pestis infection most commonly results in bubonic plague, but can cause septicaemic or pneumonic plagues.
The Black Death most likely originated in Central Asia or East Asia, from where it travelled along the Silk Road, reaching Crimea by 1347. From there, it was most likely carried by fleas living on the black rats that travelled on Genoese merchant ships, spreading throughout the Mediterranean Basin and reaching Africa, Western Asia, and the rest of Europe via Constantinople, Sicily, and the Italian Peninsula. Current evidence indicates that once it came onshore, the Black Death was in large part spread by human fleas – which cause pneumonic plague – and the person-to-person contact via aerosols which pneumonic plague enables, thus explaining the very fast inland spread of the epidemic, which was faster than would be expected if the primary vector was rat fleas causing bubonic plague.
There are no exact figures for the death toll, the rate varied widely by locality. In urban centres, the greater the population before the outbreak, the longer the duration of the period of abnormal mortality. It killed some 75 to 200 million people in Eurasia. The mortality rate of the Black Death in the 14th century was far greater than the worst 20th-century outbreaks of Y. pestis plague, which occurred in India and killed as much as 3% of the population of certain cities.
Although academic debate continues, no single alternative solution has achieved widespread acceptance. Many scholars arguing for Y. pestis as the major agent of the pandemic suggest that its extent and symptoms can be explained by a combination of bubonic plague with other diseases, including typhus, smallpox and respiratory infections. In addition to the bubonic infection, others point to additional septicaemic (a type of "blood poisoning") and pneumonic (an airborne plague that attacks the lungs before the rest of the body) forms of the plague, which lengthen the duration of outbreaks throughout the seasons and help account for its high mortality rate and additional recorded symptoms. In 2014, Public Health England announced the results of an examination of 25 bodies exhumed in the Clerkenwell area of London, as well as of wills registered in London during the period, which supported the pneumonic hypothesis. Currently, while osteoarcheologists have conclusively verified the presence of Y. pestis bacteria in burial sites across northern Europe through examination of bones and dental pulp, no other epidemic pathogen has been discovered to bolster the alternative explanations. In the words of one researcher: "Finally, plague is plague."

Cholera outbreak 1820
Seven cholera pandemics have occurred in the past 200 years, with the first pandemic originating in India in 1817. Additionally, there have been many documented cholera outbreaks, such as a 1991–1994 outbreak in South America and, more recently, the 2016–20 Yemen cholera outbreak.
Between 1816 and 1923, the first six cholera pandemics occurred consecutively and continuously over time. Increased commerce, migration, and pilgrimage are credited for its transmission. Late in this period (particularly 1879-1883), major scientific breakthroughs towards the treatment of cholera develop: the first immunization by Pasteur, the development of the first cholera vaccine, and the identification of the bacterium Vibrio cholerae by Filippo Pacini and Robert Koch. After a long hiatus, the seventh cholera pandemic spread in 1961. The pandemic subsided in 1970s, but continued on a smaller scale, with outbreaks across the developing world to the current day. Epidemics occurred after wars, civil unrest, or natural disasters, when water and food supplies become contaminated with Vibrio cholerae, and also due to crowded living conditions and poor sanitation.
The first cholera pandemic occurred in the Bengal region of India, near Calcutta starting in 1817 through 1824. The disease dispersed from India to Southeast Asia, the Middle East, Europe, and Eastern Africa through trade routes. The second pandemic lasted from 1826 to 1837 and particularly affected North America and Europe due to the result of advancements in transportation and global trade, and increased human migration, including soldiers. The third pandemic erupted in 1846, persisted until 1860, extended to North Africa, and reached South America, for the first time specifically affecting Brazil. The fourth pandemic lasted from 1863 to 1875 spread from India to Naples and Spain. The fifth pandemic was from 1881–1896 and started in India and spread to Europe, Asia, and South America. The sixth pandemic started in India and was from 1899–1923. These epidemics were less fatal due to a greater understanding of the cholera bacteria. Egypt, the Arabian peninsula, Persia, India, and the Philippines were hit hardest during these epidemics, while other areas, like Germany in 1892 and Naples from 1910–1911, also experienced severe outbreaks. The seventh pandemic originated in 1961 in Indonesia and is marked by the emergence of a new strain, nicknamed El Tor, which still persists (as of 2019) in developing countries.
A persistent urban myth states 90,000 people died in Chicago of cholera and typhoid fever in 1885, but this story has no factual basis. In 1885, a torrential rainstorm flushed the Chicago River and its attendant pollutants into Lake Michigan far enough that the city's water supply was contaminated. But, as cholera was not present in the city, there were no cholera-related deaths. As a result of the pollution, the city made changes to improve its treatment of sewage and avoid similar events.


Spanish flu 1920
The Spanish flu, also known as the 1918 flu pandemic, was an unusually deadly influenza pandemic caused by the H1N1 influenza A virus. Lasting more than 12 months from spring 1918 (northern hemisphere) to early summer 1919, it infected 500 million people – about a third of the world's population at the time. The death toll is estimated to have been anywhere from 17 million to 50 million, and possibly as high as 100 million, making it one of the deadliest pandemics in human history.
To maintain morale, World War I censors minimized early reports of illness and mortality in Germany, the United Kingdom, France, and the United States. Newspapers were free to report the epidemic's effects in neutral Spain, such as the grave illness of King Alfonso XIII, and these stories created a false impression of Spain as especially hard hit. This gave rise to the name "Spanish" flu
One of the few regions of the world seemingly less affected by the 1918 flu pandemic was China, where several studies have documented a comparatively mild flu season in 1918. (Although this is disputed due to lack of data during the country's Warlord Period, see Around the globe). This has led to speculation that the 1918 flu pandemic originated in China, as the lower rates of flu mortality may be explained by the Chinese population's previously acquired immunity to the flu virus.
Some have suggested that the epidemic originated in the United States. Historian Alfred W. Crosby stated in 2003 that the flu originated in Kansas, and popular author John M. Barry described a January 1918 outbreak in Haskell County, Kansas, as the point of origin in his 2004 article.
A report published in 2016 in the Journal of the Chinese Medical Association found evidence that the 1918 virus had been circulating in the European armies for months and possibly years before the 1918 pandemic. Political scientist Andrew Price-Smith published data from the Austrian archives suggesting the influenza began in Austria in early 1917.


Coronavirus 2020
Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans, these viruses cause respiratory tract infections that can range from mild to lethal. Mild illnesses include some cases of the common cold (which is caused also by certain other viruses, predominantly rhinoviruses), while more lethal varieties can cause SARS, MERS, and COVID-19. Symptoms in other species vary: in chickens, they cause an upper respiratory tract disease, while in cows and pigs they cause diarrhea. There are as yet no vaccines or antiviral drugs to prevent or treat human coronavirus infections.
Coronaviruses were first discovered in the 1930s when an acute respiratory infection of domesticated chickens was shown to be caused by infectious bronchitis virus (IBV). Arthur Schalk and M.C. Hawn described in 1931 a new respiratory infection of chickens in North Dakota. The infection of new-born chicks was characterized by gasping and listlessness.
Human coronaviruses were discovered in the 1960s. They were isolated using two different methods in the United Kingdom and the United States. E.C. Kendall, Malcom Byone, and David Tyrrell working at the Common Cold Unit of the British Medical Research Council in 1960 isolated from a boy a novel common cold virus B814.
In December 2019, a pneumonia outbreak was reported in Wuhan, China. On 31 December 2019, the outbreak was traced to a novel strain of coronavirus, which was given the interim name 2019-nCoV by the World Health Organization (WHO), later renamed SARS-CoV-2 by the International Committee on Taxonomy of Viruses.
Infection begins when the viral spike protein attaches to its complementary host cell receptor. After attachment, a protease of the host cell cleaves and activates the receptor-attached spike protein. Depending on the host cell protease available, cleavage and activation allows the virus to enter the host cell by endocytosis or direct fusion of the viral envelop with the host membrane.
As of 19 May 2020, there have been at least 318,554 confirmed deaths and more than 4,805,430 confirmed cases in the coronavirus pneumonia pandemic. The Wuhan strain has been identified as a new strain of Betacoronavirus from group 2B with approximately 70% genetic similarity to the SARS-CoV. The virus has a 96% similarity to a bat coronavirus, so it is widely suspected to originate from bats as well. The pandemic has resulted in travel restrictions and nationwide lockdowns in several countries.

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