The+spread+of+disease

The Spread of Disease
Disease diffusion refers to the spread of the disease from its source into new areas. The incidence of a disease is likely to be affected by distance such that places closer to the source of the disease are more likely to see higher infection rates. Disease diffusion has been classified into a number of types.
 * 1) **Expansion diffusion**. Expansion diffusion occurs when a disease spreads from one place to another. In this expansion process, the disease often intensifies in the originating region. However, as the disease expands into new areas, it is likely to weaken. This type of diffusion was recognized in the recent H1N1 flu that had its source in Mexico.
 * 2) **Relocation diffusion**. Relocation diffusion is a spatial/geographic spread process, whereby the disease leaves the areas in which it originated as it moves into new areas. An example can be seen in the migration of disease carriers with HIV or Measles. The spread of cholera in Haiti in 2010 was thought to be brought into the country by aid workers from Nepal.
 * 3) **Network diffusion**. Network diffusion occurs when the disease spreads through transportation and social networks. An example is the diffusion of HIV which spread along important transport routes in Southern African countries with developed road networks, as well as social (sexual) networks. Second and third examples are the recent H1N1 flu virus and Ebola virus which quickly went global via the aviation network of flights and major international airports.
 * 4) **Contagious diffusion**. Contagious diffusion spread depends on direct contact. It is a type of diffusion whereby the process is strongly influenced by distance, because nearby individuals or regions tend to have a much higher probability of contact or infection (incidence of the disease) than remote individuals or regions.
 * 5) **Hierarchical diffusion**. It involves the spread of disease through an ordered sequence of classes or places, for example from large cities to remote villages. Cascade diffusion is a term used to describe a process assumed to be downwards from larger cities to smaller centres.

Concept of Barriers
** Barriers to the Spread of Disease ** Barriers of disease diffusion can be classified in terms of
 * 1) ==== Natural/physical barriers. The most important natural barrier is that of ====
 * ====** Distance decay ** . The further a place is away from the source of incidence the lower the incidence of disease. ====
 * ====** Rural peripheries **, ====
 * ====** Mountainous regions ** . Mountains and oceans also act as major natural barriers to the spread of disease as they contain people and restrict migration ====
 * ====** Regions of extreme climate ** experience relatively small amounts of in and out-migration. As a result the spread of disease into these regions is less likely. ====

2. ** Human measures ** relate to
==== i. ** isolated ** in their homes. This later became a bit of a farce as these same people were giving media interviews from their house windows. Isolation is of course an important management measure for many diseases though, and is essential for highly infectious diseases such as cholera. Other measures in the UK involved creating a ====
 * ==== socio-political structures such as **political borders and migration control**, which restrict or prevent the movement of people. US migration policy specifically prevents the immigration of foreigners who carry infectious diseases. At times of high risk borders can be completely closed, however for the economic impacts of such a measure it would need to be an extreme case. ====
 * ==== Other human controls relate to the **management of disease** and directly to the way in which a disease is transmitted. In the case of the H1N1 flu virus many measures were adapted in the UK. Initially, people who contracted the flu were ====