Lecture 21 : New Infectious Diseases (2) Overview

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).

8. 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.

10. 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.

11. North Island, New Zealand

13. Mangrove swamp

14. 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.

15. 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’.

16. 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.

17. 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.

18. 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.

19. 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).