The Spread of Disease 1 This section of the unit explores the way that diseases move. Diseases are more mobile than previously, because we are more mobile than before as a species, and we carry diseases with us. The network of communications by road, rail and air means that potential carriers of diseases (people who are still capable of infecting others with a particular disease) can travel across the globe in a matter of hours. Less than two hundred years ago, diseases travelled slowly and it was possible to quarantine an area more easily. 1918 influenza pandemic (sometimes referred to as Spanish Flu) killed an estimated 40 million people worldwide within just a few months, with some estimates of casualties closer to 90 million. AIM: To be able to explain how the geographic concepts of diffusion by relocation and by expansion apply to the spread of diseases. To examine the application of the concept of barriers in attempts to limit the spread of diseases. To describe the factors that have enabled reduction in incidence of a disease. Diffusion and transmission models Where might there be a greater risk of disease spreading? a refugee camp on the border of a war torn developing nation a favela in a South American city a densely populated hutong in Hong Kong a suburban housing estate in the United States a block of flats in Central London http://youtu.be/TcauOxevK0g Spatial Diffusion of Disease Disease diffusion refers to the spread of a disease into new locations. It occurs when incident of a disease spreads out from an initial source. Four main types of diffusion: Relocation Expansion Contagious Hierarchal Relocation Diffusion Occurs when the spreading disease moves into new areas, leaving behind it’s origin or source A person infected with HIV moving into a new location. An example of relocation of disease can be seen in the migration of disease carriers, whether it be a migrant with HIV or measles. The spread of cholera in Haiti in 2010, which killed 6000 people was thought to be brought into the country by aid workers from Nepal in the emergency response to the earthquake. Expansion diffusion Occurs when the expanding disease has a source and diffuses outwards into new areas. This type of diffusion was recognized in the recent H1N1 flu virus that had its source in Mexico. Contagious Diffusion Is the spread of an infectious disease through the direct contact of individuals with those infected The process is strongly influenced by distance because nearby individuals or regions have a much higher probability of contact than remote individuals or regions. Original map identifying the cluster and source or the cholera outbreak of Broad Street in 1852. The actual contaminated water pump has been marked with the red dot. Hierarchical Diffusion Occurs when a phenomenon spreads through an ordered sequence of classes or places From cities to large urban areas to small urban areas. Network Diffusion Network diffusion occurs when a disease spreads via transportation and social networks. A good example of a disease to explain this path of diffusion is HIV. We can see how HIV is spread along important transport routes such as those countries with a developed road network in southern Africa. A second example would be the recent H1N1 flu virus that quickly went global via the aviation network of flights and major international airports. Barriers Barriers of disease diffusion can be classified in terms of natural physical barriers and human measures. 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. Factors that slow down the spread of disease include physical barriers (these might include mountains, water barriers such as seas or oceans, forests and difficult terrain) Other natural barriers relate to remoteness. Remote regions such as rural peripheries, mountainous regions and regions of extreme climate experience relatively small amounts of in and outmigration. As a result the spread of disease into these regions is less likely. Mountains and oceans also act as major natural barriers to the spread of disease as they contain people and restrict migration. Human measures relate to 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. Isolation is of course an important management measure for many diseases though, and is essential for highly infectious diseases such as cholera. Other measures involve creating a heightened awareness of improved hygiene. People were advised to refrain from typical greeting customs such kisses and hand shakes and to wash their hands carefully. In public places like airports and railway stations people wore face masks. authorities considered cancelling larger public events such as sports events and pop concerts. These events at the time all saw reduced attendance.