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A pandemic (from Greek παν pan all + δήμος demos people) is an epidemic of infectious disease that spreads through populations across a large region; for instance a continent, or even worldwide.

Contents 1 Definition 2 Pandemics and notable epidemics through history 2.1 Cholera 2.2 Influenza 2.3 Typhus 2.4 HIV and AIDS 2.5 Effects of colonization 2.6 Unknown causes 2.7 Unit 731 3 Concern about possible future pandemics 3.1 Ebola virus and other quickly lethal diseases 3.2 Antibiotic resistance 3.3 SARS 3.4 Influenza 3.5 H5N1 4 See also 5 References 5.1 Notes 5.2 Bibliography 6 Further reading 7 External links

Definition

According to the World Health Organization (WHO), a pandemic can start when three conditions have been met:^[1]

• Emergence of a disease new to a population.
• Agents infect humans, causing serious illness.
• Agents spread easily and sustainably among humans.

A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious. For instance, cancer is responsible for many deaths but is not considered a pandemic, because the disease is not infectious or contagious.

Pandemics and notable epidemics through history

It has been suggested that this article or section be merged into Epidemic#Notable_epidemics_through_history. (Discuss)

There have been a number of significant pandemics recorded in human history, generally zoonoses which came about with domestication of animals, such as influenza and tuberculosis. There have been a number of particularly significant epidemics that deserve mention above the "mere" destruction of cities:

• Peloponnesian War, 430 BC. Typhoid fever killed a quarter of the Athenian troops, and a quarter of the population over four years. This disease fatally weakened the dominance of Athens, but the sheer virulence of the disease prevented its wider spread; i.e. it killed off its hosts at a rate faster than they could spread it. The exact cause of the plague was unknown for many years. In January 2006, researchers from the University of Athens analyzed teeth recovered from a mass grave underneath the city, and confirmed the presence of bacteria responsible for typhoid.^[2]
• Antonine Plague, 165–180. Possibly smallpox brought to the Italian peninsula by soldiers returning from the Near East; it killed a quarter of those infected, and up to five million in all. At the height of a second outbreak, the Plague of Cyprian (251–266), which may have been the same disease, 5,000 people a day were said to be dying in Rome.
• Plague of Justinian, from 541 to 750, was the first recorded outbreak of the bubonic plague. It started in Egypt, and reached Constantinople the following spring, killing (according to the Byzantine chronicler Procopius) 10,000 a day at its height, and perhaps 40% of the city's inhabitants. The plague went on to eliminate a quarter to a half of the human population that it struck throughout the known world. ^[3][4] It caused Europe's population to drop by around 50% between 550 and 700.^[5]
• Black Death, started 1300s. Eight hundred years after the last outbreak, the bubonic plague returned to Europe. Starting in Asia, the disease reached Mediterranean and western Europe in 1348 (possibly from Italian merchants fleeing fighting in the Crimea), and killed 20 to 30 million Europeans in six years;^[6] a third of the total population, and up to a half in the worst-affected urban areas.^[7]

Cholera

• First cholera pandemic 1816-1826. Previously restricted to the Indian subcontinent, the pandemic began in Bengal, then spread across India by 1820. 10,000 British troops and countless Indians died during this pandemic.^[8] It extended as far as China, Indonesia (where more than 100,000 people succumbed on the island of Java alone) and the Caspian Sea before receding. Deaths in India between 1817 and 1860 are estimated to have exceeded 15 million persons. Another 23 million died between 1865 and 1917. Russian deaths during a similar time period exceeded 2 million.^[9]
• Second cholera pandemic 1829–1851. Reached Russia (see Cholera Riots), Hungary (about 100,000 deaths) and Germany in 1831, London in 1832 (more than 55,000 persons died in the United Kingdom),^[10] France, Canada (Ontario), and United States (New York) in the same year,^[11] and the Pacific coast of North America by 1834. A two-year outbreak began in England and Wales in 1848 and claimed 52,000 lives.^[12]
• Third pandemic 1852–1860. Mainly affected Russia, with over a million deaths.
• Fourth pandemic 1863–1875. Spread mostly in Europe and Africa. At least 30,000 of the 90,000 Mecca pilgrims fell victim to the disease. Cholera claimed 90,000 lives in Russia in 1866.^[13]
• In 1866, there was an outbreak in North America.
• Fifth pandemic 1881-1896. The 1883-1887 epidemic cost 250,000 lives in Europe and at least 50,000 in Americas. Cholera claimed 267,890 lives in Russia (1892);^[14] 120,000 in Spain^[15]; 90,000 in Japan and 60,000 in Persia.
• In 1892, cholera contaminated the water supply of Hamburg, Germany, and caused 8606 deaths.^[16]
• Sixth pandemic 1899–1923. Had little effect in Europe because of advances in public health, but Russia was badly affected again (more than 500,000 people dying of cholera during the first quarter of the 20th century).^[17] The sixth pandemic killed more than 800,000 in India.
• Seventh pandemic 1962-66. Began in Indonesia, called El Tor after the strain, and reached Bangladesh in 1963, India in 1964, and the USSR in 1966.

Influenza

• First pandemic 1510. Traveled from Africa and spread across Europe.^[18][19]
• The "Asiatic Flu", 1889–1890. Was first reported in May of 1889 in Bukhara, Uzbekistan. By October, it had reached Tomsk and the Caucasus. It rapidly spread west and hit North America in December 1889, South America in February–April 1890, India in February-March 1890, and Australia in March–April 1890. It was purportedly caused by the H2N8 type of flu virus, and had a very high attack and mortality rate.
• The "Spanish flu", 1918–1919. First identified early in March 1918 in US troops training at Camp Funston, Kansas. By October 1918, it had spread to become a world-wide pandemic on all continents, and eventually infected 2.5 to 5% of the human population, with 20% or more of the world population suffering from the disease to some extent. Unusually deadly and virulent, it ended nearly as quickly as it began, vanishing completely within 18 months. In six months, some 50 million were dead; some estimates put the total of those killed worldwide at over twice that number.^[20] An estimated 17 million died in India, 675,000 in the United States^[21] and 200,000 in the UK. The virus was recently reconstructed by scientists at the CDC studying remains preserved by the Alaskan permafrost. They identified it as a type of H1N1 virus.^{[citation needed]}
• The "Asian Flu", 1957–58. An H2N2 caused about 70,000 deaths in the United States. First identified in China in late February 1957, the Asian flu spread to the United States by June 1957.
• The "Hong Kong Flu", 1968–69. An H3N2 caused about 34,000 deaths in the United States. This virus was first detected in Hong Kong in early 1968, and spread to the United States later that year. Influenza A (H3N2) viruses still circulate today.

Typhus

Typhus is sometimes called "camp fever" because of its pattern of flaring up in times of strife. (It is also known as "gaol fever" and "ship fever", for its habits of spreading wildly in cramped quarters, such as jails and ships.) Emerging during the Crusades, it had its first impact in Europe in 1489, in Spain. During fighting between the Christian Spaniards and the Muslims in Granada, the Spanish lost 3,000 to war casualties, and 20,000 to typhus. In 1528, the French lost 18,000 troops in Italy, and lost supremacy in Italy to the Spanish. In 1542, 30,000 people died of typhus while fighting the Ottomans in the Balkans.

In the Thirty Years' War, an estimated 8 million Germans were wiped out by bubonic plague and typhus fever.^[22] The disease also played a major role in the destruction of Napoleon's Grande Armée in Russia in 1812. Typhus played a major factor in the Irish Potato Famine. During the World War I, typhus epidemics have killed 150,000 in Serbia. There were about 30 million infections and 3 million deaths from epidemic typhus in Russia from 1918 to 1922. Typhus also killed numerous prisoners in the Nazi concentration camps and Soviet prisoner of war camps during World War II.

HIV and AIDS

HIV, the virus that causes AIDS, is currently a pandemic, with infection rates as high as 25% in southern and eastern Africa. Effective education about safer sexual practices and bloodborne infection precautions training have helped to slow down infection rates in several African countries sponsoring national education programs. Infection rates are rising again in Asia and the Americas. AIDS death toll in Africa may reach 90-100 million by 2025.^[23][24]

Effects of colonization

Encounters between European explorers and populations in the rest of the world often introduced local epidemics of extraordinary virulence. Disease killed the entire native (Guanches) population of the Canary Islands in the 16th century. Half the native population of Hispaniola in 1518 was killed by smallpox. Smallpox also ravaged Mexico in the 1520s, killing 150,000 in Tenochtitlán alone, including the emperor, and Peru in the 1530s, aiding the European conquerors.^[25] Measles killed a further two million Mexican natives in the 1600s. In 1618–1619, smallpox wiped out 90% of the Massachusetts Bay Native Americans.^[26] Smallpox epidemics in 1780–1782 and 1837–1838 brought devastation and drastic depopulation among the Plains Indians.^[27] Some believe that the death of up to 95% of the Native American population of the New World was caused by Old World diseases.^[28] Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.^[29]

Smallpox devastated the native population of Australia, killing around 50% of Indigenous Australians in the early years of British colonisation.^[30] It also killed many New Zealand Māori.^[31] As late as 1848–49, as many as 40,000 out of 150,000 Hawaiians are estimated to have died of measles, whooping cough and influenza. Introduced diseases, notably smallpox, nearly wiped out the native population of Easter Island.^[32] In 1875, measles killed over 40,000 Fijians, approximately one-third of the population.^[33] Ainu population decreased drastically in the 19th century, due in large part to infectious diseases brought by Japanese settlers pouring into Hokkaido.^[34]

Researchers concluded that syphilis was carried from the New World to Europe after Columbus' voyages. The findings suggested Europeans could have carried the nonvenereal tropical bacteria home, where the organisms may have mutated into a more deadly form in the different conditions of Europe.^[35] The disease was more frequently fatal than it is today. Syphilis was a major killer in Europe during the Renaissance.^[36]

As early as 1803, the Spanish Crown organized a mission (the Balmis expedition) to transport the smallpox vaccine to the Spanish colonies, and establish mass vaccination programs there.^[37] By 1832, the federal government of the United States established a smallpox vaccination program for Native Americans.^[38] From the beginning of the 20th century onwards, the elimination or control of disease in tropical countries became a driving force for all colonial powers.^[39] The sleeping sickness epidemic in Africa was arrested due to mobile teams systematically screening millions of people at risk.^[40] In the 20th century, the world saw the biggest increase in its population in human history due to lessening of the mortality rate in many countries due to medical advances.^[41] World population has grown from 1.6 billion in 1900 to an estimated 6.7 billion today.^[42]

Unknown causes

There are also a number of unknown diseases that were extremely serious but have now vanished, so the etiology of these diseases cannot be established. The cause of English Sweat in 16th-century England, which struck people down in an instant and was more greatly feared than even the bubonic plague, is still unknown.

Unit 731

During the Sino-Japanese War (1937-1945), Unit 731 of the Imperial Japanese Army conducted human experimentation on thousands, mostly Chinese. In military campaigns, the Japanese army used biological weapons on Chinese soldiers and civilians. Plague fleas, infected clothing, and infected supplies encased in bombs were dropped on various targets. The resulting cholera, anthrax, and plague were estimated to have killed around 400,000 Chinese civilians.^[43]

Concern about possible future pandemics

Ebola virus and other quickly lethal diseases

Lassa fever, Rift Valley fever, Marburg virus, Ebola virus and Bolivian hemorrhagic fever are highly contagious and deadly diseases, with the theoretical potential to become pandemics. Their ability to spread efficiently enough to cause a pandemic is limited, however, as transmission of these viruses requires close contact with the infected vector, and the vector only has a short time before death or serious illness. Furthermore, the short time between a vector becoming infectious and the onset of symptoms allows medical professionals to quickly quarantine vectors, and prevent them from carrying the pathogen elsewhere. Genetic mutations could occur, which could elevate their potential for causing widespread harm; thus close observation by contagious disease specialists is merited.

Antibiotic resistance

Antibiotic-resistant microorganisms, sometimes referred to as "superbugs", may contribute to the re-emergence of diseases which are currently well-controlled. For example, cases of tuberculosis that are resistant to traditionally effective treatments remain a cause of great concern to health professionals. The World Health Organization (WHO) reports that approximately 50 million people worldwide are infected with multiple-drug resistant tuberculosis (MDR TB), with 79 percent of those cases resistant to three or more antibiotics. In 2005, 124 cases of MDR TB were reported in the United States. Extensively drug-resistant tuberculosis (XDR TB) was identified in Africa in 2006, and subsequently discovered to exist in 17 countries, including the United States.

The plague bacterium could easily develop drug-resistance and become a major health threat.^[44] Plague epidemics have occurred throughout human history, causing over 200 million deaths worldwide. The ability to resist many of the antibiotics used against plague has been found so far in only a single case of the disease in Madagascar.^[45]

In the past 20 years, common bacteria including Staphylococcus aureus, Serratia marcescens and Enterococcus, have developed resistance to various antibiotics such as vancomycin, as well as whole classes of antibiotics, such as the aminoglycosides and cephalosporins. Antibiotic-resistant organisms have become an important cause of healthcare-associated (nosocomial) infections (HAI). In addition, infections caused by community-acquired strains of methicillin-resistant Staphylococcus aureus (MRSA) in otherwise healthy individuals, have become more frequent in recent years.

SARS

In 2003, there were concerns that SARS, a new, highly contagious form of atypical pneumonia caused by a coronavirus dubbed SARS-CoV, might become pandemic. Rapid action by national and international health authorities such as the World Health Organization helped slow transmission, and eventually broke the chain of transmission, ending the localized epidemics before they could become a pandemic. The disease has not been eradicated, however, and could re-emerge unexpectedly, warranting monitoring and case reporting of suspicious cases of atypical pneumonia.

Influenza

Wild aquatic birds are the natural hosts for a range of influenza A viruses. Occasionally, viruses are transmitted from these species to other species, and may then cause outbreaks in domestic poultry or (rarely) give rise to a human pandemic. ^{[46] [47]}

H5N1

In February 2004, avian influenza virus was detected in birds in Vietnam, increasing fears of the emergence of new variant strains. It is feared that if the avian influenza virus combines with a human influenza virus (in a bird or a human), the new subtype created could be both highly contagious and highly lethal in humans. Such a subtype could cause a global influenza pandemic, similar to the Spanish Flu, or the lower mortality pandemics such as the Asian Flu and the Hong Kong Flu.

From October 2004 to February 2005, some 3,700 test kits of the 1957 Asian Flu virus were accidentally spread around the world from a lab in the US.^[48]

In May 2005, scientists urgently call nations to prepare for a global influenza pandemic that could strike as much as 20% of the world's population.^[49]

In October 2005, cases of the avian flu (the deadly strain H5N1) were identified in Turkey. EU Health Commissioner Markos Kyprianou said: "We have received now confirmation that the virus found in Turkey is an avian flu H5N1 virus. There is a direct relationship with viruses found in Russia, Mongolia and China." Cases of bird flu were also identified shortly thereafter in Romania, and then Greece. Possible cases of the virus have also been found in Croatia, Bulgaria and the United Kingdom.^[50]

By November 2007, numerous confirmed cases of the H5N1 strain had been identified across Europe ^[51]. However, by the end of October only 59 people had died as a result of H5N1 which was atypical of previous influenza pandemics.

Avian flu cannot yet be categorized as a "pandemic", because the virus cannot yet cause sustained and efficient human-to-human transmission. Cases so far are recognized to have been transmitted from bird to human, but as of December 2006 there have been very few (if any) cases of proven human-to-human transmission. Regular influenza viruses establish infection by attaching to receptors in the throat and lungs, but the avian influenza virus can only attach to receptors located deep in the lungs of humans, requiring close, prolonged contact with infected patients, and thus limiting person-to-person transmission. The current WHO phase of pandemic alert is level 3, described as "no or very limited human-to-human transmission", according to the WHO website.

See also

• Epidemic
• List of epidemics
• List of historical plagues
• Endemic
• Syndemic
• Influenza pandemic
• Pandemic Severity Index
• Centers for Disease Control and Prevention (CDC)
• European Centre for Disease Prevention and Control (ECDC)
• Mortality from infectious diseases
• Biological warfare
• Risks to civilization, humans and planet Earth
• Medieval demography
• Globalization and disease
• Tropical disease

References

Notes

Bibliography

Further reading

External links