Transcript Spatial Diffusion of Disease

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.