Physical Factors and the Prevalence of Disease

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Global Patterns of Climate

  • Temperature determines the rates of vector (carrier of disease or medication) development and behaviour
  • Precipitation creates aquatic habitats such as ponds and stagnant pools, which allows insects and disease vectors to flourish and complete their life cycles
  • Many diseases are water-borne
  • Millions of people in developing world rely on water from wells and surface supplies contaminated by sewage
  • Unprotected and stagnant drinking water supplies also provide habitats for disease vectors (e.g. copepod vectors- transmit the parasitical disease Guinea Worm to humans in West Africa
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Global Patterns of Relief

  • Relief affects global patterns of disease as altitude cayses abrupt changes in climate and disease habitats
  • In Ethiopia, Malaria is concentrated in the humid lowlands but is largely absent in the cooler highlands.
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Seasonal Variations

  • Transmission most effective in cold temperatures and when atmospheric humidity is low
  • In nothern hemisphere epidemics of influenza (a contagious respiratory illness) peak in winter months
  • In tropics and subtropics, vector-borne diseases transmitted by mosquitoes, flies, ticks, fleas and worms often during rainy season. For example, diarrhoeal diseases in South Africa surges in pre-monsoon (march-april) and end of monsoon (september-october) periods when fly populations are highest
  • Sandflies are most abundant in the rainy season
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Physical Factors and Disease Vectors

  • In the south pacific, sustained temperatures of more than 32oC and humidity levels above 95% trigger waves of dengue epidemics.
  • These conditions occur in summer months but short term weather changes and exeptional rainfall events can also lead to outbreaks of the disease.
  • Mosquitos thrive in warm, humid conditions which in turn favours the outbreak of dengue.
  • Dengue fever is widespread in the tropics. It annualy infects around 400 million and has caused 25,000 deaths.
  • Climate controls dengue fever epidemology and the life cycle of Aede mosquitoes that transmit the dengue virus to humans
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Climate Change

  • In Africa, sleeping sickness is endemic in 36 sub-saharan countries and affects 70 million people
  • Outbreaks occur when average temperatures are betwee 20.7oC and 26.1oC
  • Transmitted to humans by the tsetse fly.
  • Climate change is increase in temperatures, rainfall and humidity
  • It has stimulated transmission of vector-borne diseases and extended their geographical range
  • As temperatures rise, sleeping sickness is likely to spread into southern Africa. According to WHO it will affect up to 77 million more people by 2090. However, the disease may dissapear from East Africa as climate may become too hot for the tsetse larvae to survive
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Zoonotic

  • Zoonotic diseases are very common. Examples include Malaria, Dengue Fever and Sleeping Sickness
  • They can be transmitted by domestic or wild animals. For example: dogs, bats, foxes, raccoons etc. can all transit rabies

The probability of zoonotic being transmitted to humans increase where:

  • There is limited control within urban areas of feral animals
  • There is prolonged contact between humans and animals
  • Vaccination of pets and domestic livestock is sparse
  • The movement of infected wild animals is unrestricted by physical or political barriers
  • Hygene and sanitation are poor (Contamination)
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