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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.
Current pandemics include HIV/AIDS and COVID-19. (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 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...)
Selected articles -
- Image 1The 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 one quarter of the population, and is believed to have entered Athens through Piraeus, the city's port and sole source of food and supplies. Much of the eastern Mediterranean also saw an outbreak of the disease, albeit with less impact.
The war, along with the plague, had serious effects on Athens' society. This resulted in a lack of adherence to laws and religious belief; in response, laws became stricter, resulting in the punishment of non-citizens claiming to be Athenian. Among the victims of the plague was Pericles, the leader of Athens. The plague returned twice more, in 429 BC and in the winter of 427/426 BC. Some 30 pathogens have been suggested as having caused the plague. (Full article...) - Image 2
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 be eradicated.
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 spread between people or 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 3The 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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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...) - Image 5
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 SARS-CoV-2 virus strain, met the requirements to be the first Disease X. (Full article...) - Image 6The 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, as well as to the Plague of Justinian which struck the Eastern Roman Empire in the early 540s.
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 7The 735–737 Japanese smallpox epidemic (天平の疫病大流行, Tenpyō no ekibyō dairyūkō, "Epidemic of the Tenpyō era") was a major smallpox epidemic that afflicted much of Japan. Killing approximately one third (around 1 million individuals) of the entire Japanese population, the epidemic had significant social, economic, and religious repercussions throughout the country. (Full article...)
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Human immunodeficiency virus infection and acquired immunodeficiency syndrome (HIV/AIDS) is a spectrum of conditions caused by infection with the human immunodeficiency virus (HIV), a retrovirus. Following initial infection an individual may not notice any symptoms, or may experience a brief period of influenza-like illness. Typically, this is followed by a prolonged incubation period with no symptoms. If the infection progresses, it interferes more with the immune system, increasing the risk of developing common infections such as tuberculosis, as well as other opportunistic infections, and tumors which are rare in people who have normal immune function. These late symptoms of infection are referred to as acquired immunodeficiency syndrome (AIDS). This stage is often also associated with unintended weight loss.
HIV is spread primarily by unprotected sex (including anal and vaginal sex), contaminated hypodermic needles or blood transfusions, and from mother to child during pregnancy, delivery, or breastfeeding. Some bodily fluids, such as saliva, sweat and tears, do not transmit the virus. Oral sex has little to no risk of transmitting the virus. Methods of prevention include safe sex, needle exchange programs, treating those who are infected, as well as both pre- and post-exposure prophylaxis. Disease in a baby can often be prevented by giving both the mother and child antiretroviral medication. (Full article...) - Image 9
The COVID-19 pandemic, also known as the coronavirus pandemic, is a global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The novel virus was first identified in an outbreak in the Chinese city of Wuhan in December 2019. Attempts to contain it there failed, allowing the virus to spread to other areas of Asia and later worldwide. The World Health Organization (WHO) declared the outbreak a public health emergency of international concern on 30 January 2020, and began referring to it as a pandemic on 11 March 2020. As of 17 May 2023, the pandemic had caused 765,902,514 cases and 6,927,365 confirmed deaths, making it one of the deadliest in history.
COVID-19 symptoms range from undetectable to deadly, but most commonly include fever, dry cough, and fatigue. Severe illness is more likely in elderly patients and those with certain underlying medical conditions. COVID-19 transmits when people breathe in air contaminated by droplets and small airborne particles containing the virus. The risk of breathing these in is highest when people are in close proximity, but they can be inhaled over longer distances, particularly indoors. Transmission can also occur if contaminated fluids reach the eyes, nose, or mouth, or, more rarely, through contaminated surfaces. Infected individuals are typically contagious for 10 days and can spread the virus even if they do not develop symptoms. Mutations have produced many strains (variants) with varying degrees of infectivity and virulence. (Full article...) - Image 10The Hong Kong flu, also known as the 1968 flu pandemic, was a flu pandemic whose outbreak in 1968 and 1969 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 plague of Justinian or Justinianic plague (541–549 AD) was the first recorded major outbreak of the first plague pandemic: the first Old World pandemic of plague, the contagious disease caused by the bacterium Yersinia pestis. The disease afflicted the entire Mediterranean Basin, Europe, and the Near East, severely affecting the Sasanian Empire and the Byzantine Empire and 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. This first episode of the first plague pandemic had profound economic, social, and political effects across Europe and the Near East.
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 closely related to the ancestor of the Justinian plague strain have 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. (Full article...) - Image 12
The global epidemic of HIV/AIDS (human immunodeficiency virus infection and acquired immunodeficiency syndrome) began in 1981, and is an ongoing worldwide public health issue. According to the World Health Organization (WHO), as of 2021, HIV/AIDS has killed approximately 40.1 million people, and approximately 38.4 million people are infected with HIV globally. Of these 38.4 million people, 75% are receiving antiretroviral treatment. There were about 770,000 deaths from HIV/AIDS in 2018, and 650,000 deaths in 2021. The 2015 Global Burden of Disease Study estimated that the global incidence of HIV infection peaked in 1997 at 3.3 million per year. Global incidence fell rapidly from 1997 to 2005, to about 2.6 million per year. Incidence of HIV has continued to fall, decreasing by 23% from 2010 to 2020, with progress dominated by decreases in Eastern Africa and Southern Africa. , there are approximately 1.5 million new infections of HIV per year globally.
According to the World Health Organization (WHO), the prevalence of HIV in the Africa Region was estimated at 1.1 million people as of 2018. The African Region accounts for two thirds of the incidence of HIV around the world. Sub-Saharan Africa is the region most affected by HIV. In 2018, an estimated 61% of new HIV infections occurred in this region, and as of 2020, more than two thirds of those living with HIV are living in Africa. HIV rates have been decreasing in the region: From 2010 to 2020, new infections in eastern and southern Africa fell by 38%. Still, South Africa has the largest population of people with HIV of any country in the world, at 8.45 million, 13.9% of the population as of 2022. As of 2022, it is estimated that the adult HIV prevalence rate is 6.2%, a 1.2% increase from data reported in the 2011 UNAIDS World Aids Day Report. (Full article...) - Image 13
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 to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future.
Vaccines can be prophylactic (to prevent or ameliorate 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 14
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 15
The 2009 swine flu pandemic, caused by the H1N1/swine flu/ influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, is the third recent flu pandemic involving the H1N1 virus (the first being the 1918–1920 Spanish flu pandemic and the second being the 1977 Russian flu). The first two cases were discovered independently in the United States in April 2009. The virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus, leading to the term "swine flu".
Some studies estimated that the real number of cases including asymptomatic and mild cases could be 700 million to 1.4 billion people—or 11 to 21 percent of the global population of 6.8 billion at the time. The lower value of 700 million is more than the 500 million people estimated to have been infected by the Spanish flu pandemic. However, the Spanish flu infected approximately a third of the world population at the time, a much higher proportion. (Full article...)
General images -
Image 1The 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 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 3Example of an epidemic showing the number of new infections over time. (from Epidemic)
Image 4Scaled 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 5First cholera pandemic (from History of cholera)
Image 6A 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 7Influenza intervals in the CDC's Pandemic Intervals Framework (from Influenza pandemic)
Image 8Estimates 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 9The 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 10Hand 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 11The 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 121892 cholera outbreak in Hamburg, hospital ward (from History of cholera)
Image 13Influenza ward at Walter Reed Hospital, in Washington, D.C., during the 1918 flu pandemic. (from Influenza pandemic)
Image 14Register of Patients Gosport Naval Hospital August 1832 cholera cases (from History of cholera)
Image 15Structure 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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