Download Introduction to the Geography of Health

An Introduction to the Geography of Health
Chapter 2: Environmental Change
and Human Health
Photo by Helen Hazen
Clear-cutting, South Australia
Ecology of Human Health
An ecological approach to
human health considers
humans as part of a broader
cycle of disease that requires
an understanding of how
environments influence
human health.
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An Introduction to the Geography of Health
Chapter 2
The natural environment refers
to components of the
environment such as soil, air,
vegetation, and water.
Photo by Peter Anthamatten
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An Introduction to the Geography of Health
Chapter 2
The built environment refers to
human-constructed parts of the
landscape such as buildings, dams,
and roads.
Photo by Peter Anthamatten
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An Introduction to the Geography of Health
Chapter 2
The social environment refers to
aspects of human behavior and
organization that comprise the social
structures within which we live.
Photo by Peter Anthamatten
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An Introduction to the Geography of Health
Chapter 2
Can you think of one way in which
each aspect of the human environment
(natural, built, and social) could
influence human health?
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An Introduction to the Geography of Health
Chapter 2
Agents of Disease
People are continually exposed to
organisms and substances that can
cause disease.
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Pathogens
Geogens
Physical hazards
Bacteria
Coal dust
Trauma
Rickettsiae
Asbestos
Extreme heat/cold
Fungi
Lead
Radiation
Anthamatten and Hazen
An Introduction to the Geography of Health
Chapter 2
Transmissibility
Can you think of other
examples of communicable
and non-communicable
diseases?
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What is the difference
between an infectious and a
contagious disease?
An Introduction to the Geography of Health
Chapter 2
Transmission Routes
Human or
animal source
of a pathogen
Direct transmission
occurs via bodily
contact or airborne
droplets.
Human or
animal recipient
of the pathogen
Indirect transmission
occurs via vectors,
food, water, soil, or
fomites.
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Chapter 2
Adaptation
The concept of adaptation can also
help explain spatial patterns of disease
in the context of human ecology.
Adaptation can be a genetic,
physiological, or behavioral process.
Can you think of an
example of each type of
adaptation?
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Chapter 2
Physiological adaptation can help
us to understand the passage of an
epidemic through a population.
An S-shaped curve is often
used to represent changes
in the number of people
infected during the
passage of an epidemic.
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An Introduction to the Geography of Health
Chapter 2
In the early part of an
epidemic few people are
infected and can act as a
source of the pathogen so the
disease spreads slowly.
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An Introduction to the Geography of Health
Chapter 2
In the mid-part of an epidemic,
the rate of new infections
increases as more and more
people become infectious.
The majority of the population is
susceptible because most people
have yet to come into contact
with the pathogen.
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An Introduction to the Geography of Health
Chapter 2
Over time, the rate at which new
infections occurs slows as much of the
population has either died or
developed immunity (physiologically
adapted) to the pathogen.
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Chapter 2
Can you think of any
historical examples of
infectious diseases that
have followed this pattern?
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An Introduction to the Geography of Health
Chapter 2
Cultural Ecology of Disease
The cultural ecology of disease is the study of how
cultural practices influence the likelihood of a
disease circulating in a particular population.
This image shows men and boys
bathing in a communal bathing tank in
the Patuakhali District, Bangladesh.
Photo by Centers for Disease Control / Michael Schwarz, 1975
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Chapter 2
Understanding the cultural ecology of
disease can shed light on key
behaviors and practices that might
slow or prevent the spread of disease.
For instance, the Hungarian doctor,
Ignaz Semmelweis, recognized the
importance of hand washing to
health in the nineteenth century.
Source: Doby (1860)
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Chapter 2
For example, Chagas
disease was not a problem
in the Amazon until
recently, perhaps due to
changing cultural practices.
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Chapter 2
Disease Cycles
An important aspect of
human ecology is the way in
which humans interact with
other species.
Many species act as vectors
or reservoirs of diseases that
infect humans.
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Source: US Department of Agriculture (2001)
An Introduction to the Geography of Health
Chapter 2
A disease cycle diagram
offers a way to visualize and
analyze disease cycles.
Boxes represent organisms or
environments in which the pathogen
must reside to complete its lifecycle.
Arrows indicate how the pathogen
moves between boxes.
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This generalized disease cycle
represents a hypothetical disease.
Pathogens such as bacteria are living
agents of disease.
Hosts such as humans are the
organisms they infect.
Vectors such as flies transmit the
pathogen between hosts.
Reservoirs act as sources of infection
and may be animate (e.g., a monkey)
or inanimate (e.g., a water body).
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Chapter 2
The disease cycle of dengue shows
that the dengue virus (the pathogen)
is transmitted from human host to
human host by a mosquito vector.
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Chapter 2
Disease cycle diagrams can
indicate where interventions
could be made to break the
disease cycle.
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Chapter 2
Landscape Epidemiology
Russian geographer E. N. Pavlovsky (1966) coined the term
“landscape epidemiology” to refer to the ways in which
regions impart patterns to disease distributions via factors
such as vegetation, geology, and climate.
Photo by Helen Hazen
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Mineral Springs, Yellowstone
An Introduction to the Geography of Health
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Elevation
Rainfall
Temperature
Landscape epidemiology suggests that factors such as
elevation and precipitation might play a key role in the
distribution of a vector-borne disease such as malaria.
Data Sources: Guerra et al. (2008), Legates and Willmott (1990)
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Chapter 2
The distribution of dengue fever is also related to climate,
providing another example of landscape epidemiology. The
mosquito vector, Aedes aegypti, is only able to survive where
year-round temperatures remain above 10oC.
Data Source: WHO (2008)
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Chapter 2
Of course, the natural environment
cannot fully explain the range of a
disease.
Schistosomiasis provides a good
example of how landscape and
human behavior interact in ways
that affect disease patterns.
Schistosomiasis affects about 200
million people worldwide and more
than 650 million people live in
endemic areas (WHO 2008b).
This map shows the distribution of
schistosomiasis in Egypt.
Image Source: Courtesy of the WHO (1987)
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The schistosomiasis
pathogen completes its
lifecycle in water, snails and
vertebrate hosts such as
people or water buffalo.
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Hosts are infected when
they come in contact with
free-swimming larvae.
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How could the
schistosomiasis disease
cycle be broken?
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Chapter 2
The Urban Environment
Region
Overcrowding and
overextended
infrastructure have
become significant
problems in places that
have experienced rapid
urbanization.
Proportion of urban
population
living in slums (%)
Developing World
Sub-Saharan Africa
Asia (excluding )
Middle East and
South America
Cen. America / Caribbean
Total
72.5
39.7
35.8
35.5
23.7
43.4
Developed World
Europe
North America
Oceania
Total
6.2
5.8
3.5
7.5
Data Source: WRI (2007)
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Diarrheal diseases such as cholera and typhoid are
significant problems in urban contexts, particularly in
slums where fresh water is lacking.
Outskirts of Lima, Peru
Photo by Heike Alberts
Outskirts of Esparza, Costa Rica
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An Introduction to the Geography of Health
Photo by Peter Anthamatten
Chapter 2
Urban environments have also proved to be ideal for
some disease-spreading pests such as rats.
The mosquitoes that carry dengue fever thrive in urban
contexts where trash and small containers provide an
abundance of small pools of water for breeding.
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Chapter 2
Environmental Change
Changes in vegetation and the array of species living in an
area can also alter disease distributions.
For example, malaria is spreading
in parts of the Amazon Basin
where forest has been converted
to cattle pasture, improving
breeding conditions for the
mosquito vector.
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For example, Lyme disease may be
spreading in the northeast US as
landscape change alters the
species balance of the region and
more settlements are built in periurban settings where the tick
vector is common.
An Introduction to the Geography of Health
Chapter 2
Climate change may have a variety of impacts on human
health associated with changes in temperature, precipitation,
vegetation, and atmospheric patterns.
How, more specifically,
might climate change
influence human health?
Photo by Helen Hazen
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Chapter 2
Impacts of climate change on human health may include:
Warmer temperatures may increase
the altitudinal and latitudinal range
of certain vectors.
More extreme weather events may
have direct impacts on health such
as through trauma, as well as lead to
ecological disruption with associated
health impacts.
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Changing rainfall patterns and
related vegetation distributions may
alter the range of vectors.
Changes in the composition of the
atmosphere may increase
respiratory pollutants like ozone.
More frequent heat waves may
increase heat-related deaths.
An Introduction to the Geography of Health
Chapter 2
Discussion Questions
1.
2.
3.
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How is cultural ecology important in the transmission of dengue fever?
Using specific examples, consider whether the built environment or the
natural environment influences human health more profoundly.
Considering recent events, can you identify any evidence that suggests a
link between climate change and health?
Anthamatten and Hazen
An Introduction to the Geography of Health
Chapter 2
References
Centers for Disease Control and Schwarz, M. (1975) “Image ID# 12356” Public Health Image Library [Online]. Available:
<http://phil.cdc.gov/phil/download.asp> (Accessed 10 Jan 2011).
Doby, J. Ignaz Phillip Semmelweis. Copper engraving.
Guerra, C. A., Gikandi, P. W., Tatem, A. J., Noor, A. M., Smith, D. L., Hay, S. I. and Snow, R. W. (2008) "The limits and
intensity of Plasmodium falciparum transmission: Implications for malaria control and elimination worldwide", Plos
Medicine, 5: 300–11.
Legates, D. R. and Willmott, C. J. (1990) "Mean seasonal and spatial variability in gauge-corrected, global precipitation",
International Journal of Climatology, 10: 111–27.
United States Department of Agriculture. (2001). “Aedes aegypti (Linnaeus) yellow fever mosquito” Agricultural Research
Service Image Gallery. [Online]. Available: <http://www.sel.barc.usda.gov/selhome/gbu/aedes.html> (Accessed 12
December 2010).
[WHO] World Health Organization. (1987) Atlas of the Global Distribution of Schistosomiasis. [Online]. Available:
<http://www.who.int/wormcontrol/documents/maps/en/egypt.pdf> (Accessed 03 Aug 2010).
WHO. (2008) Schistosomiasis: A Major Public Health Problem [Online]. Available:
<http://www.who.int/schistosomiasis/en/index.html> (Accessed 23 December 2009).
[WRI] World Resources Institute. (2007) EarthTrends Database: The Environmental Information Portal [Online]. Available:
<http://earthtrends.wri.org/searchable_db/index.php?theme=4> (Accessed 31 December 2008).
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