Portal:Pandemics
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The Pandemics and Epidemics Portal
A pandemic (/pænˈdɛmɪk/ pan-DEM-ik) is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. Widespread endemic diseases with a stable number of infected individuals such as recurrences of seasonal influenza are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide.
Throughout human history, there have been a number of pandemics of diseases such as smallpox. The most fatal pandemic in recorded history was the Black Death—also known as The Plague—which killed an estimated 75–200 million people in the 14th century. The term had not been used then but was used for later epidemics, including the 1918 influenza pandemic—more commonly known as the Spanish flu. The most recent pandemics include the HIV/AIDS pandemic, the 2009 H1N1 pandemic and the COVID-19 pandemic. Almost all these diseases still circulate among humans though their impact now is far less.
In response to the COVID-19 pandemic, recently 194 member states of the World Health Organization began negotiations on an International Treaty on Pandemic Prevention, Preparedness and Response with a requirement to submit a draft of this treaty to the 77th World Health Assembly during its 2024 convention. This is expected to set rules for dealing with a pandemic by the international community. (Full article...)
An epidemic (from Greek ἐπί epi "upon or above" and δῆμος demos "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.
Epidemics of infectious disease are generally caused by several factors including a change in the ecology of the host population (e.g., increased stress or increase in the density of a vector species), a genetic change in the pathogen reservoir or the introduction of an emerging pathogen to a host population (by movement of pathogen or host). Generally, an epidemic occurs when host immunity to either an established pathogen or newly emerging novel pathogen is suddenly reduced below that found in the endemic equilibrium and the transmission threshold is exceeded.
An epidemic may be restricted to one location; however, if it spreads to other countries or continents and affects a substantial number of people, it may be termed as a pandemic. The declaration of an epidemic usually requires a good understanding of a baseline rate of incidence; epidemics for certain diseases, such as influenza, are defined as reaching some defined increase in incidence above this baseline. A few cases of a very rare disease may be classified as an epidemic, while many cases of a common disease (such as the common cold) would not. An epidemic can cause enormous damage through financial and economic losses in addition to impaired health and loss of life. (Full article...)
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The Cocoliztli Epidemic or the Great Pestilence was an outbreak of a mysterious illness characterized by high fevers and bleeding which caused 5–15 million deaths in New Spain during the 16th century. The Aztec people called it cocoliztli, Nahuatl for pestilence. It ravaged the Mexican highlands in epidemic proportions, resulting in the demographic collapse of some Indigenous populations.
Based on the death toll, this outbreak is often referred to as the worst epidemic in the history of Mexico. Subsequent outbreaks continued to baffle both Spanish and native doctors, with little consensus among modern researchers on the pathogenesis. However, recent bacterial genomic studies have suggested that Salmonella, specifically a serotype of Salmonella enterica known as Paratyphi C, was at least partially responsible for this initial outbreak. Others believe cocoliztli was caused by an indigenous viral hemorrhagic fever, perhaps exacerbated by the worst droughts to affect that region in 500 years and poor living conditions for Indigenous peoples of Mexico following the Spanish conquest (c. 1519). (Full article...) - Image 2
The plague of Justinian or Justinianic plague (AD 541–549) was an epidemic that afflicted the entire Mediterranean Basin, Europe, and the Near East, severely affecting the Sasanian Empire and the Byzantine Empire, especially Constantinople. The plague is named for the Byzantine Emperor Justinian I (r. 527–565), who according to his court historian Procopius contracted the disease and recovered in 542, at the height of the epidemic which killed about a fifth of the population in the imperial capital. The contagion arrived in Roman Egypt in 541, spread around the Mediterranean Sea until 544, and persisted in Northern Europe and the Arabian Peninsula until 549. By 543, the plague had spread to every corner of the empire. As the first episode of the first plague pandemic, it had profound economic, social, and political effects across Europe and the Near East and cultural and religious impact on Eastern Roman society.
In 2013, researchers confirmed earlier speculation that the cause of the plague of Justinian was Yersinia pestis, the same bacterium responsible for the Black Death (1346–1353). Ancient and modern Yersinia pestis strains are closely related to the ancestor of the Justinian plague strain that has been found in the Tian Shan, a system of mountain ranges on the borders of Kyrgyzstan, Kazakhstan, and China, suggesting that the Justinian plague originated in or near that region. However, there would appear to be no mention of bubonic plague in China until the year 610. (Full article...) - Image 3
The Black Death was a bubonic plague pandemic occurring in Europe from 1346 to 1353. One of the most fatal pandemics in human history, as many as 50 million people perished, perhaps 50% of Europe's 14th century population. Bubonic plague is caused by the bacterium Yersinia pestis and spread by fleas. One of the most significant events in European history, the Black Death had far-reaching population, economic, and cultural impacts.
The Black Death was the beginning of the second plague pandemic. The plague created religious, social and economic upheavals, with profound effects on the course of European history. (Full article...) - Image 4
Epidemic typhus, also known as louse-borne typhus, is a form of typhus so named because the disease often causes epidemics following wars and natural disasters where civil life is disrupted. Epidemic typhus is spread to people through contact with infected body lice, in contrast to endemic typhus which is usually transmitted by fleas.
Though typhus has been responsible for millions of deaths throughout history, it is still considered a rare disease that occurs mainly in populations that suffer unhygienic extreme overcrowding. Typhus is most rare in industrialized countries. It occurs primarily in the colder, mountainous regions of central and east Africa, as well as Central and South America. The causative organism is Rickettsia prowazekii, transmitted by the human body louse (Pediculus humanus corporis). Untreated typhus cases have a fatality rate of approximately 40%. (Full article...) - Image 5
The Antonine Plague of AD 165 to 180, also known as the Plague of Galen (after Galen, the Greek physician who described it), was a prolonged and destructive epidemic, which impacted the Roman Empire. It was possibly contracted and spread by soldiers who were returning from campaign in the Near East. Scholars generally believe the plague was smallpox, although measles has also been suggested, and recent genetic evidence strongly suggests that smallpox only arose much later. In AD 169 the plague may have claimed the life of the Roman emperor Lucius Verus, who was co-regnant with Marcus Aurelius. These two emperors had risen to the throne by virtue of being adopted by the previous emperor, Antoninus Pius, and as a result, their family name, Antoninus, has become associated with the pandemic.
Ancient sources agree that the plague is likely to have appeared during the Roman siege of the Mesopotamian city of Seleucia in the winter of 165–166, during the Parthian campaign of Lucius Verus. Ammianus Marcellinus reported that the plague spread to Gaul and to the legions along the Rhine. Eutropius stated that a large proportion of the empire's population died from this outbreak. According to the contemporary Roman historian Cassius Dio, the disease broke out again 9 years later in 189 AD and caused up to 2,000 deaths a day in the city of Rome, 25% of those who were affected. The total death count has been estimated at 5–10 million, roughly 10% of the population of the empire. The disease was particularly deadly in the cities and in the Roman army. (Full article...) - Image 6Crimson Contagion was a joint exercise conducted from January to August 2019, in which numerous national, state and local, private and public organizations in the US participated, in order to test the capacity of the federal government and twelve states to respond to a severe pandemic of influenza originating in China.
The simulation, which was conducted by the Department of Health and Human Services in a series of exercises that ran from January to August 2019, involved a scenario in which a group of about 30 tourists returning from China spread a novel influenza A respiratory virus in the United States, beginning in Chicago. In less than two months the virus had spread from a single index case (a 52-year-old man returning to Chicago) to infect 110 million Americans; 7.7 million patients would require hospitalization, and 586,000 people would die from the novel virus. The 70-page report issued at the conclusion of the exercise outlined the government's limited capacity to respond to a pandemic. States experienced "multiple challenges" requesting resources from the federal government "due to a lack of standardized, well-understood, and properly executed resource request processes," the report said. Federal agencies lacked the funds, coordination, and capacities to implement an effective response to the virus. (Full article...) - Image 7
The third plague pandemic was a major bubonic plague pandemic that began in Yunnan, China, in 1855. This episode of bubonic plague spread to all inhabited continents, and ultimately led to more than 12 million deaths in India and China (and perhaps over 15 million worldwide), and at least 10 million Indians were killed in British Raj India alone, making it one of the deadliest pandemics in history. According to the World Health Organization, the pandemic was considered active until 1960 when worldwide casualties dropped to 200 per year. Plague deaths have continued at a lower level for every year since.
The name refers to the third of at least three known major plague pandemics. The first began with the Plague of Justinian, which ravaged the Byzantine Empire and surrounding areas in 541 and 542; the pandemic persisted in successive waves until the middle of the 8th century. The second began with the Black Death, which killed at least one third of Europe's population in a series of expanding waves of infection from 1346 to 1353; this pandemic recurred regularly until the 19th century. (Full article...) - Image 8
Seven cholera pandemics have occurred in the past 200 years, with the first pandemic originating in India in 1817. The seventh cholera pandemic is officially a current pandemic and has been ongoing since 1961, according to a World Health Organization factsheet in March 2022. Additionally, there have been many documented major local cholera outbreaks, such as a 1991–1994 outbreak in South America and, more recently, the 2016–2021 Yemen cholera outbreak.
Although much is known about the mechanisms behind the spread of cholera, this has not led to a full understanding of what makes cholera outbreaks happen in some places and not others. Lack of treatment of human feces and lack of treatment of drinking water greatly facilitate its spread. Bodies of water have been found to serve as a reservoir, and seafood shipped long distances can spread the disease. (Full article...) - Image 9
Disease X is a placeholder name that was adopted by the World Health Organization (WHO) in February 2018 on their shortlist of blueprint priority diseases to represent a hypothetical, unknown pathogen that could cause a future epidemic. The WHO adopted the placeholder name to ensure that their planning was sufficiently flexible to adapt to an unknown pathogen (e.g., broader vaccines and manufacturing facilities). Director of the US National Institute of Allergy and Infectious Diseases Anthony Fauci stated that the concept of Disease X would encourage WHO projects to focus their research efforts on entire classes of viruses (e.g., flaviviruses), instead of just individual strains (e.g., zika virus), thus improving WHO capability to respond to unforeseen strains. In 2020, experts, including some of the WHO's own expert advisors, speculated that COVID-19, caused by the SARS-CoV-2 virus strain, met the requirements to be the first Disease X. (Full article...) - Image 10The 1957–1958 Asian flu pandemic was a global pandemic of influenza A virus subtype H2N2 that originated in Guizhou in Southern China. The number of excess deaths caused by the pandemic is estimated to be 1–4 million around the world (1957–1958 and probably beyond), making it one of the deadliest pandemics in history. A decade later, a reassorted viral strain H3N2 further caused the Hong Kong flu pandemic (1968–1969). (Full article...)
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A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and recognize further and destroy any of the microorganisms associated with that agent that it may encounter in the future.
Vaccines can be prophylactic (to prevent or alleviate the effects of a future infection by a natural or "wild" pathogen), or therapeutic (to fight a disease that has already occurred, such as cancer). Some vaccines offer full sterilizing immunity, in which infection is prevented completely. (Full article...) - Image 12
The history of smallpox in Mexico spans approximately 430 years from the arrival of the Spanish to the official eradication in 1951. It was brought to what is now Mexico by the Spanish, then spread to the center of Mexico, where it became a significant factor in the fall of Tenochtitlan. During the colonial period, there were major epidemic outbreaks which led to the implementation of sanitary and preventive policy. The introduction of smallpox vaccination in New Spain by Francisco Javier de Balmis and the work of Ignacio Bartolache reduced the mortality and morbidity of the disease. (Full article...) - Image 13The first plague pandemic was the first historically recorded Old World pandemic of plague, the contagious disease caused by the bacterium Yersinia pestis. Also called the early medieval pandemic, it began with the Plague of Justinian in 541 and continued until 750 or 767; at least fifteen or eighteen major waves of plague following the Justinianic plague have been identified from historical records. The pandemic affected the Mediterranean Basin most severely and most frequently, but also infected the Near East and Northern Europe, and potentially East Asia as well. The Roman emperor Justinian I's name is sometimes applied to the whole series of plague epidemics in late Antiquity.
The pandemic is best known from its first and last outbreaks: the Justinianic Plague of 541–549, described by the contemporary Roman historian Procopius, and the late 8th century plague of Naples described by Neapolitan historian John the Deacon in the following century (distinct from the much later Naples Plague). Other accounts from contemporaries of the pandemic are included in the texts of Evagrius Scholasticus, John of Ephesus, Gregory of Tours, Paul the Deacon, and Theophanes the Confessor; most seem to have believed plague was a divine punishment for human misdeeds. (Full article...) - Image 14
Smallpox was an infectious disease caused by variola virus (often called smallpox virus), which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) certified the global eradication of the disease in 1980, making smallpox the only human disease to have been eradicated to date.
The initial symptoms of the disease included fever and vomiting. This was followed by formation of ulcers in the mouth and a skin rash. Over a number of days, the skin rash turned into the characteristic fluid-filled blisters with a dent in the center. The bumps then scabbed over and fell off, leaving scars. The disease was transmitted from one person to another primarily through prolonged face-to-face contact with an infected person or (rarely) via contaminated objects. Prevention was achieved mainly through the smallpox vaccine. Once the disease had developed, certain antiviral medications could potentially have helped, but such medications did not become available until after the disease was eradicated. The risk of death was about 30%, with higher rates among babies. Often, those who survived had extensive scarring of their skin, and some were left blind. (Full article...) - Image 15
The third cholera pandemic (1846–1860) was the third major outbreak of cholera originating in India in the 19th century that reached far beyond its borders, which researchers at University of California, Los Angeles (UCLA) believe may have started as early as 1837 and lasted until 1863. In the Russian Empire, more than one million people died of cholera. In 1853–1854, the epidemic in London claimed over 10,000 lives, and there were 23,000 deaths for all of Great Britain. This pandemic was considered to have the highest fatalities of the 19th-century epidemics.
It had high fatalities among populations in Asia, Europe, Africa and North America. In 1854, which was considered the worst year, 23,000 people died in Great Britain. (Full article...)
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- Image 2By 12 February 2009, the number of cases of infection by cholera in sub-Saharan Africa had reached 128,548 and the number of fatalities, 4,053. (from History of cholera)
- Image 3The difference between the influenza mortality age-distributions of the 1918 epidemic and normal epidemics. Deaths per 100,000 persons in each age group, United States, for the interpandemic years 1911–1917 (dashed line) and the pandemic year 1918 (solid line). (from Influenza pandemic)
- Image 4The Plague of Athens (c. 1652–1654) by Michiel Sweerts, illustrating the devastating epidemic that struck Athens in 430 BC, as described by the historian Thucydides (from Epidemic)
- Image 5A pump memorializing John Snow for his study of contaminated water as a likely source of cholera during the 1854 Broad Street Cholera outbreak (from History of cholera)
- Image 6Example of an epidemic showing the number of new infections over time. (from Epidemic)
- Image 7First cholera pandemic (from History of cholera)
- Image 8Influenza ward at Walter Reed Hospital, in Washington, D.C., during the 1918 flu pandemic. (from Influenza pandemic)
- Image 9Influenza intervals in the CDC's Pandemic Intervals Framework (from Influenza pandemic)
- Image 10Structure of the influenza viron. The hemagglutinin (HA) and neuraminidase (NA) proteins are shown on the surface of the particle. The viral RNAs that make up the genome are shown as red coils inside the particle and bound to Ribonuclear Proteins (RNPs). (from Influenza pandemic)
- Image 11Scaled examples of past influenza pandemics and past influenza seasons. Color scheme included to represent corresponding estimates of hypothetical influenza deaths in the 2010 US population, with the same color scale as the previous figure. (from Pandemic Severity Assessment Framework)
- Image 12Anopheles mosquito, the vector of malaria (from Epidemic)
- Image 13Estimates of hypothetical influenza deaths in the 2010 United States population (308,745,538 persons) across varying values of case-fatality ratio and the cumulative incidence of infection in the population. Selected estimated numbers of deaths are indicated with a black line, across each relevant combination of case-fatality ratio and cumulative incidence. In addition, the background color transitions from blue to yellow to red as the estimated absolute number of deaths increases. Case-fatality ratio is an example of a clinical severity measure and cumulative incidence of infection is an example of a transmissibility measure in the Pandemic Severity Assessment Framework. (from Pandemic Severity Assessment Framework)
- Image 14Patients suffering from cholera in 1854 (from History of cholera)
- Image 15Bodies of Rwandan refugees who died during the cholera epidemic, October 1994 (from History of cholera)
- Image 17Register of Patients Gosport Naval Hospital August 1832 cholera cases (from History of cholera)
- Image 18Hand bill from the New York City Board of Health, 1832. The outdated public health advice demonstrates the lack of understanding of the disease and its actual causative factors. (from History of cholera)
- Image 19The various types of influenza viruses in humans. Solid squares show the appearance of a new strain, causing recurring influenza pandemics. Broken lines indicate uncertain strain identifications. (from Influenza pandemic)
- Image 20Possibilities for zoonotic disease transmissions (from Epidemic)
- Image 21Disposal of dead bodies during the cholera epidemic in Palermo in 1835 (from History of cholera)
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