Disease Diffusion

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Disease Diffusion

  • Disease Diffusion- Diseases spread outwards from their origin and across space in a process known as diffusion.
  • The four types of disease diffusion are: Expansion, Relocation, Contagious and Hierarchial.
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Expansion Diffusion

  • Occurs when a disease spreads from one place to another
  • In this expansion process, the disease often intesifies in the originating region.
  • As the disease expands into new areas it is likely to weaken
  • An example is the tuberculosis outbreak

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Relocation Diffusion

  • A spatial spread process, whereby the disease leaves the areas in which it originated as it moves into new areas.
  • An example is the spread of cholera in Haiti (2010) (6,000 killed) where the disease was thought to be bought into Haiti by aid workers from Nepal in the emergency response to the earthquake.

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Contagious Diffusion

  • Depends on human contact.
  • Process strongly influenced by distance because nearby individuals or regions have a much higher probability of contact than remote individuals or regions.

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Hierarchical Diffusion

  • Involves the spread of disease through an ordered sequence of classes or places (e.g. large cities to remote villages)
  • This spread can be seen with HIV in regard to social status and sexual habits -> Starts with high status and high concurrency of sexual relations, spreading to medium and then lower [Status refers to sexual appeal and personality traits]

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Barriers to Diffusion

  • Climate: is a major factor in the epidemiology and distribution of diseases such as malaria and sleeping sickness.
  • Screening and Quarantine: Mass vaccination programmes protect populations against diseases such as flu and health education consitutes additional barriers to the spread of disease.
  • Political Barriers: Political Borders check the international movements of carriers of infectious disease.
  • Distance: The probability of a contagious disease spreading to an area is inversely proportional to distance from its source.
  • Physical Barriers: e.g. Mountain Ranges
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