A pandemic (/pænˈdɛmɪk/ pan-DEM-ik) is an epidemic of an infectious disease that has a sudden increase in cases and spreads 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 Black Death, caused by the Plague, caused the deaths of up to half of the population of Europe in the 14th century. The term pandemic had not been used then, but was used for later epidemics, including the 1918 H1N1 influenza A pandemic—more commonly known as the Spanish flu—which is the deadliest pandemic in history. The most recent pandemics include the HIV/AIDS pandemic, the 2009 swine flu pandemic and the COVID-19 pandemic. Almost all these diseases still circulate among humans though their impact now is often far less.
In response to the COVID-19 pandemic, 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. Further, on 6 May 2024, the White House released an official policy to more safely manage medical research projects involving potentially hazardous pathogens, including viruses and bacteria, that may pose a risk of a pandemic. (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 Plague of Athens (Ancient Greek: Λοιμὸς τῶν Ἀθηνῶν, Loimos tôn Athênôn) was an epidemic that devastated the city-state of Athens in ancient Greece during the second year (430 BC) of the Peloponnesian War when an Athenian victory still seemed within reach. The plague killed an estimated 75,000 to 100,000 people, around 25% of the population, and is believed to have entered Athens through Piraeus, the city's port and sole source of food and supplies. Thucydides, an Athenian survivor, wrote that much of the eastern Mediterranean also saw an outbreak of the disease, albeit with less impact.
The war, along with the plague, had lasting effects on Athenian society. Short-term, there was civil disorder, and violations of usual funerary practices. Thucydides describes a decrease in traditional religious practices and increase in superstitious explanations. He estimates that it took 15 years for the Athenian population to recover. Long-term, the high death toll drastically redistributed wealth within Athenian society, and weakened Athens politically. (Full article...) -
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. (Full article...) -
The Black Death was a bubonic plague pandemic that occurred in Europe from 1346 to 1353. It was one of the most fatal pandemics in human history; as many as 50 million people perished, perhaps 50% of Europe's 14th century population. The disease is caused by the bacterium Yersinia pestis and spread by fleas and through the air. One of the most significant events in European history, the Black Death had far-reaching population, economic, and cultural impacts. It 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.
The origin of the Black Death is disputed. Genetic analysis suggests Yersinia pestis bacteria evolved approximately 7,000 years ago, at the beginning of the Neolithic, with flea-mediated strains emerging around 3,800 years ago during the late Bronze Age. The immediate territorial origins of the Black Death and its outbreak remain unclear, with some evidence pointing towards Central Asia, China, the Middle East, and Europe. The pandemic was reportedly first introduced to Europe during the siege of the Genoese trading port of Kaffa in Crimea by the Golden Horde army of Jani Beg in 1347. From Crimea, it was most likely carried by fleas living on the black rats that travelled on Genoese ships, spreading through the Mediterranean Basin and reaching North Africa, West Asia, and the rest of Europe via Constantinople, Sicily, and the Italian Peninsula. There is evidence that once it came ashore, the Black Death mainly spread from person-to-person as pneumonic plague, thus explaining the quick inland spread of the epidemic, which was faster than would be expected if the primary vector was rat fleas causing bubonic plague. In 2022, it was discovered that there was a sudden surge of deaths in what is today Kyrgyzstan from the Black Death in the late 1330s; when combined with genetic evidence, this implies that the initial spread may not have been due to Mongol conquests in the 14th century, as previously speculated. (Full article...) -
Saint Sebastian pleading for the life of a gravedigger afflicted with plague during the 7th-century Plague of Pavia, by South Netherlandish painter Josse Lieferinxe ca. 1498
The 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 to 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...) -
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...) -
An outbreak of cholera began in Yemen in October 2016. The outbreak peaked in 2017 with over 2,000 reported deaths in that year alone. In 2017 and 2019, war-torn Yemen accounted for 84% and 93% of all cholera cases in the world, with children constituting the majority of reported cases. As of November 2021, there have been more than 2.5 million cases reported, and more than 4,000 people have died in the Yemen cholera outbreak, which the United Nations deemed the worst humanitarian crisis in the world at that time. However, the outbreak has substantially decreased by 2021, with a successful vaccination program implemented and only 5,676 suspected cases with two deaths reported between January 1 and March 6 of 2021.
Vulnerable to water-borne diseases before the conflict, 16 months went by before a program of oral vaccines was started. The cholera outbreak was worsened as a result of the ongoing civil war and the Saudi Arabian-led intervention in Yemen against the Houthi movement that began in March 2015. Airstrikes damaged hospital infrastructure, and water supply and sanitation in Yemen were affected by the ongoing conflict. The government of Yemen stopped funding public health in 2016; sanitation workers were not paid by the government, causing garbage to accumulate, and healthcare workers either fled the country or were not paid. (Full article...) -
The 1929–1930 psittacosis pandemic, also known as the psittacosis outbreak of 1929–1930 and the great parrot fever pandemic, was a series of simultaneous outbreaks of psittacosis (parrot fever) which, accelerated by the breeding and transportation of birds in crowded containers for the purpose of trade, was initially seen to have its origin in parrots from South America. It was shortly found to have spread from several species of birds from several countries worldwide to humans between mid 1929 and early 1930. Diagnosed by its clinical features and link to birds, it affected around 750 to 800 people globally, with a mortality of 15%. Its mode of transmission to humans by mouth-to-beak contact or inhaling dried bird secretions and droppings was not known at the time. The cause, Chlamydia psittaci, which usually remains dormant in birds until activated by stress of capture and confinement, was discovered after the pandemic.
Cases of psittacosis were reported in mid 1929, in Birmingham, United Kingdom, and linked to parrots from Buenos Aires, Argentina, where an ongoing outbreak of the disease had led to cautioning bird owners to declare their sick parrots. The origin of the outbreak in the Argentine city of Córdoba was traced to an import of 5,000 parrots from Brazil. Although the Argentine parrot trade was stopped, a number of birds were illegally sold on to visitors at its seaports, with the consequence that psittacosis was transmitted to several countries. (Full article...) -
The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic that occurred in 1968 and 1969 and which killed between one and four million people globally. It is among the deadliest pandemics in history, and was caused by an H3N2 strain of the influenza A virus. The virus was descended from H2N2 (which caused the Asian flu pandemic in 1957–1958) through antigenic shift, a genetic process in which genes from multiple subtypes are reassorted to form a new virus. (Full article...)
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The 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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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...) -
The 1889–1890 pandemic, often referred to as the "Asiatic flu" or "Russian flu", was a worldwide respiratory viral pandemic. It was the last great pandemic of the 19th century, and is among the deadliest pandemics in history. The pandemic killed about 1 million people out of a world population of about 1.5 billion (0.067% of population). The most reported effects of the pandemic took place from October 1889 to December 1890, with recurrences in March to June 1891, November 1891 to June 1892, the northern winter of 1893–1894, and early 1895.
According to researchers' estimates, excess mortality from Russian influenza in the Russian Empire for the period 1889–1890 could be from 60,000 to 90,000 people, with lethality from the virus, a little more than 0.2%. (Full article...) -
The Persian plague epidemic of 1772–1773, also simply known as the Persian Plague, was a massive outbreak of plague, more specifically Bubonic plague, in the Persian Empire, which claimed around 2 million lives in total. It was one of the most devastating Plague epidemics in recorded human history. The outbreak resulted in the introduction of several quarantine measures for the first time in the Persian Gulf regions. (Full article...)
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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...) -
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...) -
Colored Scanning electron microscope (SEM) image of SARS-CoV-2, speculated in 2020 as being the first virus to create Disease X
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...)
The following are images from various pandemic- and epidemic-related articles on Wikipedia.
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Anopheles mosquito, the vector of malaria (from Epidemic)
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By 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)
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Influenza intervals in the CDC's Pandemic Intervals Framework (from Influenza pandemic)
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A 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)
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Possibilities for zoonotic disease transmissions (from Epidemic)
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Estimates 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)
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Scaled 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)
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Example of an epidemic showing the number of new infections over time. (from Epidemic)
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Disposal of dead bodies during the cholera epidemic in Palermo in 1835 (from History of cholera)
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The 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)
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Structure 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)
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Register of Patients Gosport Naval Hospital August 1832 cholera cases (from History of cholera)
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Patients suffering from cholera in 1854 (from History of cholera)
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The 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)
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Influenza ward at Walter Reed Hospital, in Washington, D.C., during the 1918 flu pandemic (from Influenza pandemic)
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1892 cholera outbreak in Hamburg, hospital ward (from History of cholera)
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Hand 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)
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The 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)
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Bodies of Rwandan refugees who died during the cholera epidemic, October 1994 (from History of cholera)
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First cholera pandemic (from History of cholera)
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