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An Introduction to the Geography of Health. Chapter 2: Environmental Change and Human Health. Clear-cutting, South Australia. Photo by Helen Hazen . Ecology of Human Health. - PowerPoint PPT Presentation
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Photo by Helen Hazen Clear-cutting, South Australia
An Introduction to the Geography of Health
Chapter 2: Environmental Changeand 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.
2 An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 2
Ecology of Human Health
3 An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 2
Photo by Peter Anthamatten
The natural environment refers to components of the
environment such as soil, air, vegetation, and water.
4 An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 2
Photo by Peter Anthamatten
The built environment refers to human-constructed parts of the
landscape such as buildings, dams, and roads.
5 An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 2
Photo by Peter Anthamatten
The social environment refers to aspects of human behavior and
organization that comprise the social structures within which we live.
Can you think of one way in which each aspect of the human environment
(natural, built, and social) could influence human health?
6 An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 2
7 Anthamatten and Hazen Chapter 2
People are continually exposed to organisms and substances that can
cause disease.
Pathogens Geogens Physical hazards
Bacteria Coal dust Trauma
Rickettsiae Asbestos Extreme heat/cold
Fungi Lead Radiation
An Introduction to the Geography of Health
Agents of Disease
8 An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 2
Can you think of other examples of communicable
and non-communicable diseases?
What is the difference between an infectious and a
contagious disease?
Transmissibility
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 29
Human or animal source of a pathogen
Indirect transmission occurs via vectors, food, water, soil, or
fomites.
Direct transmission occurs via bodily
contact or airborne droplets. Human or
animal recipient of the pathogen
Transmission Routes
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?
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 210
Adaptation
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 211
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.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 212
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.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 213
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.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 214
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.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 215
Can you think of any historical examples of
infectious diseases that have followed this pattern?
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 216
The cultural ecology of disease is the study of how cultural practices influence the likelihood of a disease circulating in a particular population.
Cultural Ecology of Disease
Photo by Centers for Disease Control / Michael Schwarz, 1975
This image shows men and boys bathing in a communal bathing tank in
the Patuakhali District, Bangladesh.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 217
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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For example, Chagas disease was not a problem
in the Amazon until recently, perhaps due to
changing cultural practices.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 219
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. Source: US Department of Agriculture (2001)
Disease Cycles
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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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The disease cycle of dengue shows that the dengue virus (the pathogen)
is transmitted from human host to human host by a mosquito vector.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 223
Disease cycle diagrams can indicate where interventions could be made to break the
disease cycle.
An Introduction to the Geography of Health24 Anthamatten and Hazen Chapter 2
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
Landscape Epidemiology
Mineral Springs, Yellowstone
Anthamatten and Hazen Chapter 225
Elevation Rainfall
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.
Temperature
Data Sources: Guerra et al. (2008), Legates and Willmott (1990)
An Introduction to the Geography of Health
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.
Anthamatten and Hazen Chapter 226
Data Source: WHO (2008)
An Introduction to the Geography of Health
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 227
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)
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 228
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.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 230
How could the schistosomiasis disease
cycle be broken?
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An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 232
RegionProportion of urban
populationliving in slums (%)
Developing World Sub-Saharan Africa 72.5 Asia (excluding ) 39.7 Middle East and 35.8 South America 35.5 Cen. America / Caribbean 23.7 Total 43.4
Developed World Europe 6.2 North America 5.8 Oceania 3.5 Total 7.5
Overcrowding and overextended
infrastructure have become significant
problems in places that have experienced rapid
urbanization.
The Urban Environment
Data Source: WRI (2007)
Diarrheal diseases such as cholera and typhoid are significant problems in urban contexts, particularly in
slums where fresh water is lacking.
Photo by Heike Alberts
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Photo by Peter Anthamatten
Outskirts of Lima, Peru
Outskirts of Esparza, Costa Rica
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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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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.
Environmental Change
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 peri-
urban settings where the tick vector is common.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 236
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
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 237
Impacts of climate change on human health may include:
More frequent heat waves may increase heat-related deaths.
Changing rainfall patterns and related vegetation distributions may
alter the range of vectors.
Warmer temperatures may increase the altitudinal and latitudinal range
of certain vectors.
Changes in the composition of the atmosphere may increase
respiratory pollutants like ozone.
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.
An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 238
1. How is cultural ecology important in the transmission of dengue fever?2. Using specific examples, consider whether the built environment or the
natural environment influences human health more profoundly.3. Considering recent events, can you identify any evidence that suggests a
link between climate change and health?
Discussion Questions
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ReferencesCenters 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).