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Lecture 21 : New Infectious Diseases (2) Overview

Underlying Causes Population Growth Globalisation. Direct Causes Urbanisation Agricultural Expansion Ecological Changes Water Pollution Global Warming Ozone Hole Public Health Deficiencies War Transport. Lecture 21 : New Infectious Diseases (2) Overview. Population Increase.

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Lecture 21 : New Infectious Diseases (2) Overview

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  1. Underlying Causes Population Growth Globalisation Direct Causes Urbanisation Agricultural Expansion Ecological Changes Water Pollution Global Warming Ozone Hole Public Health Deficiencies War Transport Lecture 21 : New Infectious Diseases (2) Overview

  2. Population Increase • The world's population increased from 1.5 to 6 billion during the 20th century. By 2050 it may rise to 10 billion. • This has numerous knock-on effects.

  3. Globalisation • More and more places are being integrated into a single capitalist world economy. • This economy is inherently exploitive, both locally (i.e. class) and globally (i.e. core-periphery).

  4. Urbanisation • Urbanisation at the end of the Neolithic and at the beginning of the Industrial Revolution was associated with an upsurge in infectious diseases. • 98 percent of the world’s people were farmers and villagers in 1800. • Soon half of the world’s population will be urbanites, many living in mega-cities of 10 million or more at high densities. • This will create massive problems of water supply, sanitation and waste disposal - i.e. ideal conditions for diseases to remain endemic. • Cities will act as a springboard for epidemics to infect other areas, including developed countries.

  5. Manilla, Phillipines

  6. Expansion Into New Areas • Population pressure is forcing people to colonise new areas, especially tropical forests. • Two thirds of all the species of life on earth live in the rain forests. • Most have long-established symbiotic relationships with micro organisms. • If the host population is disrupted, humans may become the new host, possibly with devastating effects (cf. Marburg, Ebola).

  7. Ecological Change • As forests are felled, wetlands drained or savannahs are cultivated, rodents that thrive on the seeds of these crops or scavenge off human waste proliferate. • Examples: Lassa fever, Hantaan fever, South American haemorrhagic fevers, Kyasanur Forest disease. • In Asia, irrigation and wet farming breeds mosquitoes that carry malaria and dengue. • Reforestation led to emergence of Lyme disease. • Aswan dam (1970) caused Rift Valley fever and upsurge in schistosomiasis.

  8. Water Pollution • Pollution from sewage and nitrogen and phosphorus fertilisers causes eutrophication. • Algae consume oxygen, threatening other lifeforms. • Algae host bacteria and viruses, which exchange DNA to create new strains. • Algae in Sea of Bengal home to El Tor cholera vibrio which are ‘activated’ in freshwater river estuaries. • Cholera in algae in Sea of Bengal mutated to more threatening O139 strain.

  9. North Island, New Zealand

  10. Mangrove swamp

  11. Global Warming • CO2, CH4 and N2O pollution has created a greenhouse effect. • 100m people may be displaced from coastal areas by 2100. • Areas susceptible to flooding will be flooded more frequently and more severely. • Mosquitoes are already moving into areas further from the tropics and also to higher altitudes. • The number of malaria cases may increase by 50-80 million per year by 2025. • Britain and Ireland could see a return of malaria, and possibly even yellow fever and dengue; USA can expect Chagas disease. • Growth cycles of vectors will speed up, increasing likelihood of insecticide resistance.

  12. Ozone Hole • Ozone layer in upper atmosphere is being depleted by chlorofluorocarbon (CFC) gases. • More of the Sun’s UV is getting through. • UV kills plankton, food source for fish. • UV kills cyanobacteria, essential for rice to grow. • UV increases risks of cancer, especially skin cancer. • UV intensifies mutations in plant life and algae microbes, increasing the risks of new ‘super bugs’.

  13. Public Health Deficiencies • Public health in Third World countries is under-resourced due to poverty. • Do not have the resources to adequately provide clean water, process sewage, eradicate vectors, provide vaccines, etc. • Even in developed countries public health is under-resourced relative to therapeutic medicine.

  14. War • Wars often result in collapse of public health. • STDs common due to rape. • HIV infection in Africa in 1980s tended to correspond to conflict zones, with knock-on implications for malaria and tuberculosis. • Wars cause mass population movements. • Refugee camps often very unhealthy.

  15. Transport • Air transport makes it very easy to transmit a disease from one part of the world to another. • Ventilation systems within aircraft facilitate airborne infections.

  16. Other Changes • Any change may have health implications. • Some changes reduce health problems – e.g. malaria was reduced in 18th century by introduction of three field system. • May also increase health problems in unanticipated ways – e.g. air conditioning systems (Legionaires disease), plastic bags and containers (as breeding grounds for mosquitoes).

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