Pandemic

A pandemic or global epidemic is an outbreak of an infectious disease that affects people or animals over an extensive geographical area (from Greek pan all + demos people).

Common killers and pandemics

A disease is not pandemic specifically because it kills a lot of people. For example, the class of diseases known as cancer is responsible for a large number of deaths, but cancer is not considered a pandemic because it is not infectious (even though certain infectious agents are known to increase cancer risk).

Pandemics through history

• Peloponnesian War, 430 BCE. An unknown agent 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.

• Antonine Plague, 165-180. Possibly smallpox brought back from the Near East; killed a quarter of those infected and up to five million in all. At the height of a second outbreak (251-266) 5,000 people a day were said to be dying in Rome.

• Plague of Justinian, started 541. 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 per cent of the city's inhabitants. It went on to destroy up to a quarter of the human population of the eastern Mediterranean.

• The 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 twenty million Europeans in six years, a quarter of the total population and up to a half in the worst-affected urban areas.

• Cholera
• *first pandemic 1816-1826. Previously restricted to the Indian subcontinent, the pandemic began in Bengal, then spread across India by 1820. It extended as far as China and the Caspian Sea before receding.
• *The second pandemic (1829-1851) reached Europe, London in 1832, New York in the same year, and the Pacific coast of North America by 1834.
• *The third pandemic (1852-1860) mainly affected Russia, with over a million deaths.
• *The fourth pandemic (1863-1875) spread mostly in Europe and Africa.
• *The sixth pandemic (1899-1923) had little effect in Europe because of advances in public health, but Russia was badly affected again.
• *The seventh pandemic began in Indonesia in 1961, called El Tor after the strain, and reached Bangladesh in 1963, India in 1964, and the USSR in 1966.

• The "Spanish Flu", 1918-1919. Began in August 1918 in three disparate locations: Brest, Boston and Freetown. An unusually severe and deadly strain of influenza spread worldwide. The disease spread across the world, killing 25 million in the course of six months; some estimates put the total of those killed worldwide at over twice that number. An estimated 17 million died in India, 500,000 in the USA and 200,000 in the UK. It vanished within 18 months and the actual strain was never determined, though some recent attempts at reconstructing genes from the virus have been successful.

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. Measles killed a further two million Mexican natives in the 1600s. 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.

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. Examples include the previously mentioned plague in 430 BCE Greece and the English Sweat in 16th-century England, which struck people down in an instant and was more greatly feared even than the bubonic plague.

Concern about possible future pandemics

Diseases that may possibly attain pandemic proportions include Lassa fever, Rift Valley fever, Marburg virus, Ebola virus and Bolivian haemorrhagic fever. As of 2002, however, the recent emergence of these diseases into the human population has shown their virulence is high, such that they tend to 'burn out' in geographically confined areas or that their effect on humans is currently limited.

HIV - the virus that causes AIDS - can be considered a global pandemic but it is currently most extensive in southern and eastern Africa. It is restricted to a small proportion of the population in other countries, and is only spreading slowly in those countries. If there was to be a true destruction-of-life pandemic it would be likely to be similar to HIV, i.e. a constantly evolving disease.

Antibiotic-resistant superbugs may also revive diseases previously regarded as 'conquered'.

In 2003, there were concerns that SARS, a new highly contagious form of pneumonia, might have become pandemic.

In February 2004, avian influenza virus was detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. It is feared that if the avian influenza virus undergoes antigenic shift with a human influenza virus, 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 the Asian Flu and the Hong Kong Flu.

In November 2004 the director for the western region of the World Health Organization said that an influenza pandemic was inevitable and called for urgent plans to combat the virus. (Reuters)

See also