Chapter 3: Demographic Change and Emerging and Resurgent Infectious Diseases Photo by Heike Alberts Cairo, Egypt An Introduction to the Geography of Health.

Chapter 3: Demographic Change and Emerging and Resurgent Infectious Diseases

Photo by Heike AlbertsCairo, Egypt

An Introduction to the Geography of Health

2 An Introduction to the Geography of HealthAnthamatten and Hazen Chapter 3

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.

The Demographic and Epidemiologic Transitions

Data from United Nations (2009), United Nations and Department of Social and Economic Affairs (2009)


The United Nations estimates that population growth will not stabilize until

at least the mid-twenty-first century.


Human population size and structure are influenced by patterns of fertility and mortality.

The Demographic Transition Model

An Introduction to the Geography of Health5 Anthamatten and Hazen Chapter 3

The population growth rate is the difference between the

birth rate and the death rate.


In the first stage, both birth rates and death rates fluctuate at high

levels, leading to little or no population growth.


In stage two, advances in sanitation and medicine lead to a rapid decline in the death rate, but birth rates remain high.

The growing gap between high birth rates

and decreasing death rates increases the

population growth rate.


In stage three, processes of modernization lead to declining birth rates.

As the birth rate declines, population growth slows.


In stage four, low birth rates and low death rates mean growth rates remain near zero.

Population growth approaches zero as both birth and death rates are

now low.


Some scholars have argued that a fifth stage should be added to the model to include industrial societies that are

experiencing negative natural growth.


Can you think of examples of countries that fit each stage of the model?

What limitations or problems do you see with the model?


In low-income countries, infectious diseases cause a large proportion of deaths.

Low-Income CountriesCause of death Proportion (%)Lower respiratory infections 11.2Coronary heart disease 9.4Diarrheal diseases 6.9HIV/AIDS 5.7Stroke/cerebrovascular diseases 5.6Chronic obstructive pulmonary disease 3.6Tuberculosis 3.5Neonatal infections 3.4Malaria 3.3Prematurity and low birth weight 3.2

Epidemiologic Transition

Data Source: WHO 2008


With industrialization and greater wealth, the major causes of death

shift from infectious to non-infectious diseases.

This shift is known as the epidemiologic transition.

What are some of the factors that stimulate this health transition?

High-Income CountriesCause of death Proportion (%)Coronary heart disease 16.3Stroke/cerebrovascular diseases 9.3Trachea, bronchus, lung cancers 5.9Lower respiratory infections 3.8Chronic obstructive pulmonary disease 3.5Alzheimer and other dementias 3.4Colon and rectum cancers 3.3Diabetes mellitus 2.8Breast cancer 2.0Stomach cancer 1.8



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 CountriesCause of death Proportion (%)Stroke/cerebrovascular diseases 14.2Coronary heart disease 13.9Chronic obstructive pulmonary disease 7.4Lower respiratory infections 3.8Trachea, bronchus, lung cancers 2.9Road traffic accidents 2.8Hypertensive heart disease 2.5Stomach cancer 2.2Tuberculosis 2.2Diabetes mellitus 2.1



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)

Pathogen and Vector Populations

A CDC worker working with an influenza virus in 1968.


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.

Antibiotic Resistance


How have human activities encouraged the development

of antibiotic resistance?

Although pathogens evolve in this way naturally, humans have unwittingly

facilitated the development of antibiotic-resistant pathogens.

A vaccination is administered as part of the US swine flu vaccination campaign in 1976.



In vector-borne diseases, resistance is becoming a problem in both pathogen and vector populations;

vectors are increasingly resistant to pesticides.

Data from Global Malaria Partnership (2005)

Resistance to anti-malarial drugs


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?


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.


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.



The emergence of drug resistant pathogens, such as multi-drug resistant

tuberculosis, is often associated with overuse or misuse of antibiotics.



Many vector-borne diseases, such as dengue fever and malaria, are resurging as resistance develops in

pathogen and vector populations.


Infectious diseases can be modeled geographically by considering how they spread across space.

The spread of something through space is called diffusion.

Diffusion


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.


The introduction of a phenomenon to a new

location, completely outside the current range of that phenomenon, is called relocation diffusion.




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.




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).


Human influenza strains are believed to have originated from pathogens that infect

birds and pigs.

Influenza

Image source: CDC (1997)The H5N1 (avian flu) virus is shown in gold.


Image Source: United States Navy (1918b)

Periodic outbreaks of new strains of influenza can

devastate human populations.An influenza pandemic in 1918

may have killed 50 to 100 million people.

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)


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) The H1N1 (swine flu) virus


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.

Adapted from WHO (2009)Pandemic Influenza Phases


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.


Tuberculosis


WHO region

Incidence Prevalence TB MortalityNumber (1,000s)

Rate (per 100,000)

% of total

Number (1,000s)

Rate (per 100,000)

Number (1,000s)

Rate (per 100,000)

Africa 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

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)

Adapted from WHO (2007)


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



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.

Directly Observed Therapy (DOTS) in EthiopiaImage source: WHO (2002) © WHO/P. Virot


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)

Tuberculosis

Data source: EARSS (2005)


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).

CDC. (1968) “Image ID# 8165” Public Health Image Library [Online]. Available: <http://phil.cdc.gov/phil/download.asp> (Accessed 11 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.


References

United Nations. (2009) World Population Prospects: The 2008 Revision, Executive Summary [Online]. New York: United Nations. Available: <http://esa.un.org/unpd/wpp2008/pdf/WPP2008_Executive-Summary_Edited_6-Oct-2009.pdf> (Accessed 27 December 2009).

United Nations and Department of Social and Economic Affairs. (2009) World Population Prospectus: The 2008 Revision Population Database [Online]. Available: <http://esa.un.org/unpp/index.asp> (Accessed 3 January 2010).

United States Navy. (1918a). “Photo # NH 41731-A. Influenza precaution sign at the Naval Aircraft Factory, Philadelphia” Naval Historical Center. [Online]. Available: <http://www.history.navy.mil/photos/images/h41000/h41871c.htm>

United States Navy. (1918b). “Photo # NH 41871. Crowded sleeping area at Naval Training Station, San Francisco, California” Naval Historical Center. [Online]. Available: <http://www.history.navy.mil/photos/images/h41000/h41871c.htm>

[WHO] World Health Organization. (2002) ‘Tuberculosis - DOTS, Ethiopia’ [Online]. Available: <http://www.who.int/mediacentre/multimedia/2002/eth_tb/en/index1.html> (Accessed 11 Jan 2011).

WHO. (2007) ‘’Tuberculosis’ Factsheet No. 104’ [Online]. Available: <http://www.who.int/mediacentre/factsheets/fs104/en/index.html> (Accessed 2 June 2009).

WHO. (2008) The Top Ten Causes of Death [Online]. Available: <http://www.who.int/mediacentre/factsheets/fs310_2008.pdf> (Accessed 17 April 2010).

WHO. (2009) Current WHO Phase of Pandemic Alert [Online]. Available: <http://www.who.int/csr/disease/avian_influenza/phase/en/index.html> (Accessed 13 May 2009).

Chapter 3: Demographic Change and Emerging and Resurgent Infectious Diseases Photo by Heike Alberts Cairo, Egypt An Introduction to the Geography of Health.

Documents

geography of healthanthamatten

geography of health

growth rates

low birth rates

population growth rate

high birth rates

low death rates

declining birth rates