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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
Underlying Causes

Population Growth


Direct Causes


Agricultural Expansion

Ecological Changes

Water Pollution

Global Warming

Ozone Hole

Public Health Deficiencies



Lecture 21 : New Infectious Diseases (2) Overview
population increase
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.
  • 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).
  • 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.
expansion into new areas
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).
ecological change
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.
water pollution
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.
global warming
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.
ozone hole
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’.
public health deficiencies
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.
  • 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.
  • 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.
other changes
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).