1. Photo by Helen Hazen Clear-cutting, South Australia An Introduction to the Geography of Health Chapter 2: Environmental Change and Human Health

2. 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 HazenChapter 2 Ecology of Human Health

3. 3 An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 Photo by Peter Anthamatten The natural environment refers to components of the environment such as soil, air, vegetation, and water.

4. 4 An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 Photo by Peter Anthamatten The built environment refers to human-constructed parts of the landscape such as buildings, dams, and roads.

5. 5 An Introduction to the Geography of HealthAnthamatten and HazenChapter 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.

6. 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 HazenChapter 2

7. 7 Anthamatten and HazenChapter 2 People are continually exposed to organisms and substances that can cause disease. PathogensGeogensPhysical hazards BacteriaCoal dustTrauma RickettsiaeAsbestosExtreme heat/cold FungiLeadRadiation An Introduction to the Geography of Health Agents of Disease

8. 8 An Introduction to the Geography of HealthAnthamatten and HazenChapter 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

9. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 9 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

10. 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 HazenChapter 2 10 Adaptation

11. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 11 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.

12. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 12 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.

13. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 13 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.

14. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 14 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.

15. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 15 Can you think of any historical examples of infectious diseases that have followed this pattern?

16. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 16 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.

17. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 17 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)

18. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 18 For example, Chagas disease was not a problem in the Amazon until recently, perhaps due to changing cultural practices.

19. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 19 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

20. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 20 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.

21. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 21 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).

22. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 22 The disease cycle of dengue shows that the dengue virus (the pathogen) is transmitted from human host to human host by a mosquito vector.

23. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 23 Disease cycle diagrams can indicate where interventions could be made to break the disease cycle.

24. An Introduction to the Geography of Health 24 Anthamatten and HazenChapter 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

25. Anthamatten and HazenChapter 2 25 ElevationRainfall 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

26. 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 10 o C. Anthamatten and HazenChapter 2 26 Data Source: WHO (2008) An Introduction to the Geography of Health

27. Anthamatten and HazenChapter 2 27 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)

28. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 28 The schistosomiasis pathogen completes its lifecycle in water, snails and vertebrate hosts such as people or water buffalo.

29. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 29 Hosts are infected when they come in contact with free-swimming larvae.

30. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 30 How could the schistosomiasis disease cycle be broken?

31. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 31

32. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 32 Region Proportion of urban population living in slums (%) Developing World Sub-Saharan Africa72.5 Asia (excluding )39.7 Middle East and35.8 South America35.5 Cen. America / Caribbean23.7 Total43.4 Developed World Europe6.2 North America5.8 Oceania3.5 Total7.5 Overcrowding and overextended infrastructure have become significant problems in places that have experienced rapid urbanization. The Urban Environment Data Source: WRI (2007)

33. 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 An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 33 Photo by Peter Anthamatten Outskirts of Lima, Peru Outskirts of Esparza, Costa Rica

34. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 34 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.

35. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 35 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.

36. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 36 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

37. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 37 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.

38. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 38 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

39. An Introduction to the Geography of HealthAnthamatten and HazenChapter 2 39 References Centers for Disease Control and Schwarz, M. (1975) “Image ID# 12356” Public Health Image Library [Online]. Available: (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: (Accessed 12 December 2010). [WHO] World Health Organization. (1987) Atlas of the Global Distribution of Schistosomiasis. [Online]. Available: (Accessed 03 Aug 2010). WHO. (2008) Schistosomiasis: A Major Public Health Problem [Online]. Available: (Accessed 23 December 2009). [WRI] World Resources Institute. (2007) EarthTrends Database: The Environmental Information Portal [Online]. Available: (Accessed 31 December 2008).