An Introduction to the Geography of Health
Chapter 3: Demographic Change and
Emerging and Resurgent Infectious Diseases
Photo by Heike Alberts
Cairo, Egypt
The Demographic and Epidemiologic Transitions
Human population size and
structure are clearly
influenced by patterns of
health and disease.
Lifespans have increased and
the global population grown
very rapidly in recent history.
Data from United Nations (2009), United Nations and
Department of Social and Economic Affairs (2009)
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The United Nations estimates that
population growth will not stabilize until
at least the mid-twenty-first century.
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The Demographic Transition Model
Human population size and structure are
influenced by patterns of fertility and mortality.
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The population growth rate is
the difference between the
birth rate and the death rate.
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In the first stage, both birth rates
and death rates fluctuate at high
levels, leading to little or no
population growth.
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The growing gap
between high birth rates
and decreasing death
rates increases the
population growth rate.
In stage two, advances in sanitation and medicine lead to a rapid
decline in the death rate, but birth rates remain high.
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As the birth rate declines,
population growth slows.
In stage three, processes of modernization
lead to declining birth rates.
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Population growth
approaches zero as both
birth and death rates are
now low.
In stage four, low birth rates and low death rates
mean growth rates remain near zero.
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Some scholars have argued that a fifth stage should be
added to the model to include industrial societies that are
experiencing negative natural growth.
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Can you think of examples of countries
that fit each stage of the model?
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What limitations or problems do
you see with the model?
An Introduction to the Geography of Health
Chapter 3
Epidemiologic Transition
In low-income countries, infectious diseases
cause a large proportion of deaths.
Low-Income Countries
Cause of death
Lower respiratory infections
Coronary heart disease
Diarrheal diseases
HIV/AIDS
Stroke/cerebrovascular diseases
Chronic obstructive pulmonary disease
Tuberculosis
Neonatal infections
Malaria
Prematurity and low birth weight
Proportion (%)
11.2
9.4
6.9
5.7
5.6
3.6
3.5
3.4
3.3
3.2
Data Source: WHO 2008
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With industrialization and greater
wealth, the major causes of death
shift from infectious to noninfectious diseases.
This shift is known as the
epidemiologic transition.
What are some of the factors that
stimulate this health transition?
High-Income Countries
Cause of death
Coronary heart disease
Stroke/cerebrovascular diseases
Trachea, bronchus, lung cancers
Lower respiratory infections
Chronic obstructive pulmonary disease
Alzheimer and other dementias
Colon and rectum cancers
Diabetes mellitus
Breast cancer
Stomach cancer
Proportion (%)
16.3
9.3
5.9
3.8
3.5
3.4
3.3
2.8
2.0
1.8
Data Source: WHO 2008
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Many middle-income countries now face a
“double burden of disease” in the face of
rapid industrialization, as they cope with both
infectious disease and diseases of affluence.
Middle-Income Countries
Cause of death
Stroke/cerebrovascular diseases
Coronary heart disease
Chronic obstructive pulmonary disease
Lower respiratory infections
Trachea, bronchus, lung cancers
Road traffic accidents
Hypertensive heart disease
Stomach cancer
Tuberculosis
Diabetes mellitus
Proportion (%)
14.2
13.9
7.4
3.8
2.9
2.8
2.5
2.2
2.2
2.1
Data Source: WHO 2008
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Pathogen and Vector Populations
It is not only characteristics of the
host population that are important
for understanding trends in human
infectious diseases.
Pathogens and vectors can evolve
rapidly, making them a challenging
target for drug and vaccine
manufacturers.
Image source: CDC (1968)
A CDC worker working with an
influenza virus in 1968.
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Antibiotic Resistance
Antibiotic resistance emerges when antibiotics kill the most
susceptible bacteria in a population. The remaining
individuals, with higher levels of resistance to the antibiotic,
are able to breed rapidly, thereby increasing the proportion
of antibiotic-resistant bacteria in the population.
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Although pathogens evolve in this way
naturally, humans have unwittingly
facilitated the development of antibioticresistant pathogens.
How have human activities
encouraged the development
of antibiotic resistance?
Image source: CDC (1976)
A vaccination is administered as part of the US
swine flu vaccination campaign in 1976.
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Resistance to anti-malarial drugs
Data from Global Malaria
Partnership (2005)
In vector-borne diseases, resistance is becoming a
problem in both pathogen and vector populations;
vectors are increasingly resistant to pesticides.
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Emergent and Resurgent Infectious Disease
Infectious disease continue to be responsible for
more than one-third of deaths worldwide.
Additionally, a large number of new infectious
diseases have emerged since the 1940s.
The following slides show the spatial distribution
of several types of emerging infectious disease
over recent decades.
How might we explain the patterns we observe?
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Adapted from Jones et al. (2008: 993). Reprinted by permission from Macmillan Publishers Ltd: [Nature]
(Jones, K. et al. Global trends in emerging infectious diseases." Nature 451(7181): 990-994) © 2008
Zoonotic pathogens can cross from wildlife to human
populations when humans settle or hunt in wildlands.
E.g., HIV/AIDS may have entered human populations during
the butchering of wild monkeys.
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Adapted from Jones et al. (2008: 993). Reprinted by permission from Macmillan Publishers Ltd: [Nature]
(Jones, K. et al. Global trends in emerging infectious diseases." Nature 451(7181): 990–94) © 2008
Zoonotic pathogens from non-wildlife sources typically cross
into human populations from agricultural systems.
E.g., domestic poultry were the likely source of pathogens
responsible for recent avian flu outbreaks.
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Adapted from Jones et al. (2008: 993). Reprinted by permission from Macmillan Publishers Ltd: [Nature]
(Jones, K. et al. Global trends in emerging infectious diseases." Nature 451(7181): 990–94) © 2008
The emergence of drug resistant
pathogens, such as multi-drug resistant
tuberculosis, is often associated with
overuse or misuse of antibiotics.
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Adapted from Jones et al. (2008: 993). Reprinted by permission from Macmillan Publishers Ltd: [Nature]
(Jones, K. et al. Global trends in emerging infectious diseases." Nature 451(7181): 990–94) © 2008
Many vector-borne diseases, such as dengue fever and
malaria, are resurging as resistance develops in
pathogen and vector populations.
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Diffusion
Infectious diseases can be modeled geographically by
considering how they spread across space.
The spread of something through space is called diffusion.
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The spread of a
phenomenon across space,
passed through interactions
between one person and his
or her neighbor is called
expansion diffusion.
The "x" symbolizes the original source
of the phenomenon; the circles
symbolize settlements—larger circles
represent larger settlements.
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The introduction of a
phenomenon to a new
location, completely outside
the current range of that
phenomenon, is called
relocation diffusion.
The "x" symbolizes the original source
of the phenomenon; the circles
symbolize settlements—larger circles
represent larger settlements.
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Hierarchical diffusion is the
spread of a phenomenon
along hierarchical
settlement patterns.
The phenomenon is more
likely to move into large
cities before small villages.
The "x" symbolizes the original source
of the phenomenon; the circles
symbolize settlements—larger circles
represent larger settlements.
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How would you describe
diffusion patterns of the
SARS virus?
An apparently new virus that emerged
in China in 2003 eventually led to
outbreaks as far away as Canada.
Airline transportation was implicated
in the rapid spread of the new
disease, named severe acute
respiratory syndrome (SARS).
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Influenza
Human influenza strains are
believed to have originated
from pathogens that infect
birds and pigs.
The H5N1 (avian flu) virus
is shown in gold.
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Image source: CDC (1997)
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Periodic outbreaks of new
strains of influenza can
devastate human populations.
An influenza pandemic in 1918
may have killed 50 to 100
million people.
Image Source: United States Navy (1918b)
Both of these images were taken
during World War I. Sneeze
screens were erected to prevent
the spread of influenza in
barracks (above). Soldiers were
asked not to spit (left).
Image Source: United States Navy (1918a)
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In March 2009, an influenza
outbreak began in Mexico.
Popularly referred to as “swine
flu,” the influenza strain
responsible (H1N1) was
capable of infecting humans,
causing concern that a
pandemic might follow,
although this never transpired.
Image source: CDC (2009)
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The H1N1 (swine flu) virus
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Pandemic Influenza Phases
Adapted from WHO (2009)
Concerns over potential influenza pandemics center on the possibility of a
new virus emerging from animals to which humans have little immunity.
If this strain were then to evolve the ability to spread among humans, a
pandemic could occur, as illustrated here.
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Tuberculosis
Tuberculosis (TB) may have infected
human populations since antiquity.
It is estimated that one-third of the
global population may be infected
with TB, but these infections only
become active disease under
certain conditions.
Image source: CDC (1982)
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Tuberculosis is often considered to be a disease of poverty
because factors such as poor living conditions and inadequate
diet can transform a dormant infection into an active disease.
Most active cases, therefore, occur in the low-income world.
Global estimated TB incidence, prevalence, and mortality (2005)
Incidence
Prevalence
TB Mortality
Number
(1,000s)
Rate (per
100,000)
% of
total
Number
(1,000s)
Rate (per
100,000)
Number
(1,000s)
Rate (per
100,000)
2,529
343
29
3,773
511
544
74
Americas
352
39
4
448
50
49
6
E Mediterranean
565
104
6
881
163
112
21
Europe
445
50
5
525
60
66
7
SW Asia
2,993
181
34
4,809
290
512
31
Western Pacific
1,927
110
22
3,616
206
295
17
Global
8,811
136
100
14,052
217
1,577
24
WHO region
Africa
Adapted from WHO (2007)
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A major problem with TB is that the
course of treatment is extremely
long and people often stop drug
regimens before they are complete.
This has led to the development of
many drug-resistant strains of TB.
Tuberculosis testing at a
mobile clinic, 1963
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Image source: CDC (1963)
Chapter 3
In treating drug-resistant
strains several different drugs
are often administered.
Additionally, many places
have adopted directly
observed therapy (DOTS) to
make sure that people
complete the drug regimen.
Image source: WHO (2002) © WHO/P. Virot
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Directly Observed Therapy
(DOTS) in Ethiopia
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Tuberculosis
Drug-resistance is a significant
problem in high-income
contexts as well.
Staphylococcus aureus is an
example of a nosocomial
infection, one that commonly
occurs in healthcare settings,
that has evolved drug
resistant strains.
Geographic variation in resistance
to methicillin-resistant
Staphylococcus aureus (MRSA)
Data source: EARSS (2005)
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References
[CDC] Centers for Disease Control. (1963) “Image ID# 1438” Public Health Image Library [Online]. Available:
<http://phil.cdc.gov/phil/download.asp> (Accessed 11 August 2010).
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(Accessed 11 August 2010).
CDC. (1976) “Image ID# 8372” Public Health Image Library [Online]. Available: <http://phil.cdc.gov/phil/download.asp>
(Accessed 11 August 2010).
CDC. (1982) “Image ID# 4716” Public Health Image Library [Online]. Available: <http://phil.cdc.gov/phil/download.asp>
(Accessed 12 August 2010).
CDC. (1997) “Image ID# 8372” Public Health Image Library [Online]. Available: <http://phil.cdc.gov/phil/download.asp>
(Accessed 11 August 2010).
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(Accessed 12 August 2010).
[EARSS] European Antimicrobial Resistance Surveillance System. (2005) Annual Report, 2004 [Online]. Available:
<http://www.rivm.nl/earss/Images/EARSS%20annual%20report%202004%20webversie_tcm61-25345.pdf> (Accessed 26
February 2010).
Global Malaria Partnership. (2005) World Malaria Report 2005, Geneva: WHO, UNICEF.
Jones, K. E., Patel, N. G., Levy, M. A., Storeygard, A., Balk, D., Gittleman, J. L. and Daszak, P. (2008) ‘Global trends in
emerging infectious diseases’, Nature, 451: 990–93.
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References
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(Accessed 27 December 2009).
United Nations and Department of Social and Economic Affairs. (2009) World Population Prospectus: The 2008 Revision
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United States Navy. (1918a). “Photo # NH 41731-A. Influenza precaution sign at the Naval Aircraft Factory, Philadelphia”
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United States Navy. (1918b). “Photo # NH 41871. Crowded sleeping area at Naval Training Station, San Francisco,
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