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

2 Anthamatten and HazenChapter 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)

3 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 The United Nations estimates that population growth will not stabilize until at least the mid-twenty-first century.

4 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 Human population size and structure are influenced by patterns of fertility and mortality. The Demographic Transition Model

An Introduction to the Geography of Health 5 Anthamatten and HazenChapter 3 The population growth rate is the difference between the birth rate and the death rate.

6 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 In the first stage, both birth rates and death rates fluctuate at high levels, leading to little or no population growth.

7 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

8 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 In stage three, processes of modernization lead to declining birth rates. As the birth rate declines, population growth slows.

9 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

10 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 Some scholars have argued that a fifth stage should be added to the model to include industrial societies that are experiencing negative natural growth.

11 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 Can you think of examples of countries that fit each stage of the model? What limitations or problems do you see with the model?

12 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 In low-income countries, infectious diseases cause a large proportion of deaths. Low-Income Countries Cause of deathProportion (%) Lower respiratory infections11.2 Coronary heart disease9.4 Diarrheal diseases6.9 HIV/AIDS5.7 Stroke/cerebrovascular diseases5.6 Chronic obstructive pulmonary disease3.6 Tuberculosis3.5 Neonatal infections3.4 Malaria3.3 Prematurity and low birth weight3.2 Epidemiologic Transition Data Source: WHO 2008

13 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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 Countries Cause of deathProportion (%) Coronary heart disease16.3 Stroke/cerebrovascular diseases9.3 Trachea, bronchus, lung cancers5.9 Lower respiratory infections3.8 Chronic obstructive pulmonary disease3.5 Alzheimer and other dementias3.4 Colon and rectum cancers3.3 Diabetes mellitus2.8 Breast cancer2.0 Stomach cancer1.8 Data Source: WHO 2008

14 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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 deathProportion (%) Stroke/cerebrovascular diseases14.2 Coronary heart disease13.9 Chronic obstructive pulmonary disease7.4 Lower respiratory infections3.8 Trachea, bronchus, lung cancers2.9 Road traffic accidents2.8 Hypertensive heart disease2.5 Stomach cancer2.2 Tuberculosis2.2 Diabetes mellitus2.1 Data Source: WHO 2008

15 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

16 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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

17 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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 Image source: CDC (1976)

18 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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

19 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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?

20 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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): ) © 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.

21 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

22 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

23 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

24 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 Infectious diseases can be modeled geographically by considering how they spread across space. The spread of something through space is called diffusion. Diffusion

25 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

26 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

27 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

28 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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).

29 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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.

30 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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)

31 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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

32 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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

33 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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) Tuberculosis

34 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 WHO region IncidencePrevalenceTB Mortality Number (1,000s) Rate (per 100,000) % of total Number (1,000s) Rate (per 100,000) Number (1,000s) Rate (per 100,000) Africa2, , Americas E Mediterranean Europe SW Asia2, , Western Pacific1, , Global8, , ,57724 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)

35 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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 Image source: CDC (1963)

36 An Introduction to the Geography of HealthAnthamatten and HazenChapter 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. Directly Observed Therapy (DOTS) in Ethiopia Image source: WHO (2002) © WHO/P. Virot

37 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 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)

38 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 References [CDC] Centers for Disease Control. (1963) “Image ID# 1438” Public Health Image Library [Online]. Available: (Accessed 11 August 2010). CDC. (1968) “Image ID# 8165” Public Health Image Library [Online]. Available: (Accessed 11 August 2010). CDC. (1976) “Image ID# 8372” Public Health Image Library [Online]. Available: (Accessed 11 August 2010). CDC. (1982) “Image ID# 4716” Public Health Image Library [Online]. Available: (Accessed 12 August 2010). CDC. (1997) “Image ID# 8372” Public Health Image Library [Online]. Available: (Accessed 11 August 2010). CDC. (2009) “Image ID# 11214” Public Health Image Library [Online]. Available: (Accessed 12 August 2010). [EARSS] European Antimicrobial Resistance Surveillance System. (2005) Annual Report, 2004 [Online]. Available: (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.

39 An Introduction to the Geography of HealthAnthamatten and HazenChapter 3 References United Nations. (2009) World Population Prospects: The 2008 Revision, Executive Summary [Online]. New York: United Nations. Available: (Accessed 27 December 2009). United Nations and Department of Social and Economic Affairs. (2009) World Population Prospectus: The 2008 Revision Population Database [Online]. Available: (Accessed 3 January 2010). United States Navy. (1918a). “Photo # NH A. Influenza precaution sign at the Naval Aircraft Factory, Philadelphia” Naval Historical Center. [Online]. Available: United States Navy. (1918b). “Photo # NH Crowded sleeping area at Naval Training Station, San Francisco, California” Naval Historical Center. [Online]. Available: [WHO] World Health Organization. (2002) ‘Tuberculosis - DOTS, Ethiopia’ [Online]. Available: (Accessed 11 Jan 2011). WHO. (2007) ‘’Tuberculosis’ Factsheet No. 104’ [Online]. Available: (Accessed 2 June 2009). WHO. (2008) The Top Ten Causes of Death [Online]. Available: (Accessed 17 April 2010). WHO. (2009) Current WHO Phase of Pandemic Alert [Online]. Available: (Accessed 13 May 2009).