Disease Triangle

4 Key excerpts on "Disease Triangle"

• 

  eBook - ePub

  Epidemiology For Dummies

  • Amal K. Mitra(Author)
  • 2023(Publication Date)
  • For Dummies

    (Publisher)

  epidemiologic triad .

  This chapter looks more closely at these three factors of the epidemiologic triangle for an acute disease model and a chronic disease model. I explain how climate changes affect health, and I examine four vector-borne diseases that are mostly affected by climate changes.

  Scrutinizing an Acute Disease Model

  The epidemiologic triangle, first introduced as a traditional model for infectious diseases, is the simplest model (Figure 6-1a ) of all models that look at what causes an acute and infectious disease.

  © John Wiley & Sons, Inc.

  FIGURE 6-1: The agent-host-environment model.

  Here are the parts of the triangle:

  • Agent: The cause of the disease
  • Susceptible host: Either humans or animals who are victims of the disease
  • Environment: Where both the agent and the host live and interplay
    A suitable environment also helps the agent to grow and multiply, and in a favorable situation, the agent enters the host to cause a disease. In other words, the environment keep the balance. The environment factor works like a fulcrum of the balance between the agent on one side and the host on the other side, as shown in Figure 6-1b .

  If the balance between the agent and the host goes down on one side, the other side gets an upper hand. For example, if the host (the human body) gets weaker due to the loss of host immunity or host resistance, the agent gets easy access to the human body. On the other hand, if the human body grows resistance like getting a vaccine and by practicing a healthy lifestyle, then the agent fails to attack the person.

  The following sections take a closer look at the three parts of the triangle.

  Examining agent factors

  In an infectious disease model, an agent is a bacteria, virus, parasite, or fungus. Agents are infectious because they can spread from one person to another. However, some don’t infect people directly; they’re transmitted from one infected person to another through a vehicle, such as drinking contaminated water or through the bites of an insect, such as a mosquito.

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  eBook - ePub

  Epidemiology Foundations

  The Science of Public Health

  • Peter J. Fos(Author)
  • 2010(Publication Date)
  • Jossey-Bass

    (Publisher)

  3.4 shows the triangle model. The triangle depicts all aspects of causation, host, environment, and causal agent. Disease development depends on the host’s exposure to the agent (or risk factor), the strength of the agent, and the host’s susceptibility. Disease development also depends on environmental conditions: biological, social, political, and physical.

  FIGURE 3.4: Epidemiologic triangle

  Another model that depicts causation is called the wheel. The wheel of causation model has a characteristic hub, which is the host. The aspects of the model that surround the hub show the biological, social, and physical determinants of disease. This model has the ability to represent the multiple causes that are common with many diseases. Figure 3.5 shows a wheel of causation.

  FIGURE 3.5: Wheel of causation

  Summary

  In this chapter we discussed health and disease, how they are defined, and their distinction. The natural history of disease was presented with AIDS and diabetes. Disease transmission of infectious diseases was introduced. Disease causation, including the difference between sufficient and necessary causes, was discussed. The web of causation, using coronary artery disease, and the wheel of causation was described. The relationship between causal factors and disease was presented by describing the causation matrix.

  Key Terms

  Clinical course of a disease, 39 Component cause, 45 Descriptive epidemiology, 39 Direct relationships, 45 Disease, 37 Epidemiological triangle, 48 Health, 36 Health-related quality of life, 38 Hyperglycemia, 39 Indirect relationships, 45 Insulin, 40 Mental health, 36 Natural history of disease, 39 Physical health, 36 Prognosis, 39 Quality of life, 38 Sufficient cause, 45 Underdeveloped country, 40 Vector-borne transmission, 43 Vehicle-borne transmission, 42 Web of causation, 47 Wheel of causation model, 49

  Chapter Exercises 1. Define health and disease. 2. Discuss the difference between health and disease. 3. What are the two methods of disease transmission? List the types of indirect transmission. Chapter Review 1. A person can have a disease but still be considered healthy according to the definition of health. True or False? 2. Determinants of health include

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  eBook - ePub

  Global Warming and the Political Ecology of Health

  Emerging Crises and Systemic Solutions

  • Hans Baer, Merrill Singer(Authors)
  • 2016(Publication Date)
  • Routledge

    (Publisher)

  133 6

  Ecosyndemics

  The Interaction of Changing Environment and Disease

  Parasites and disease will do well on a warming earth. They are, by definition, organisms that colonize and exploit. Those species of parasite that are already common will be able to spread and perhaps colonize new susceptible hosts that may have no prior genetic resistance to them

  .

  Andrew Dobson and Robin Carper, parasitologists

  What is Disease?

  A lthough various diseases were examined in the previous three chapters, the concept of disease was not specifically defined. In that a goal of this chapter is the presentation of a broadened understanding of disease in light of the effects of global warming, the starting point is a consideration of the conventional way disease is conceived. Within biomedicine, disease is thought of as any deviation from or disruption of the normal structure or function of a body part or system, including the mind, that is characterized by a configuration of signs (detectable by physicians) and symptoms (experienced and reported by sufferers). While some diseases are recognized that have no distinct symptoms (e.g., hypertensive disease), physicians are hesitant to validate a disease known experientially to victims but undetectable to medical specialists (e.g., various folk illnesses). Critical to this model is the understanding that diseases, as distinct, bounded entities in nature, are part of an immutable physical reality and therefore have an existence independent from the social and cultural contexts in which they are found. It is for this reason that they are subject to objective description by a trained diagnostician.

  Cancer, for example, is a meta label that refers to a large number of specific diseases or kinds of cancer, all of which are characterized by the development of (observable) abnormal cells (caused by a genetic mutation) that divide uncontrollably and have the capacity to both infiltrate and destroy normal body tissue. From the perspective of biomedicine, cancer is neither a cultural construction nor is it peculiar to any individual sufferer or specific group. Rather, cancer is accepted as a bona fide component of material reality, even though it is recognized that it often is not easy to diagnose (especially in its earliest stages)—although 134

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  eBook - ePub

  Human Biology

  An Evolutionary and Biocultural Perspective

  • Sara Stinson, Barry Bogin, Dennis H. O'Rourke(Authors)
  • 2012(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  The ecology of infectious diseases, the evolution of pathogens, and the adaptations humans have made to those pathogens are important topics in anthropology, epidemiology, and biology, as are the influence of the environment on noninfectious diseases, the evolutionary reasons for the development of such conditions in both populations and individuals, and the adaptations humans have had to make in order to thrive nearly everywhere on the planet. A full discussion of these topics is beyond the scope of this chapter. However, because of their importance, we briefly introduce them and provide suggested references for interested readers who want to learn more about them. Additional examples of topics within this large and important area are provided in a few other chapters in this book (see, e.g., the discussion of sickle-cell anemia and malaria in Chapter 4).

  This vast literature on ecology, adaptation, and disease of relevance to human biology and anthropology can be divided into three major categories: studies of the ecology of health and disease, health and disease through human prehistory and history, and the evolution of diseases. Ecological studies of disease focus on the environment, both natural and human modified, and how that influences the biology of pathogens and the development and progression of both infectious and noninfectious conditions. Questions addressed in these studies include, for example, how different environments affect the relationship between hosts and their pathogens (e.g., Wills 1996), the influence of climate change on the development of diseases such as malaria, cholera, or heat-related illnesses (e.g., McMichael 2001; Patz and Olson 2006), and the impact of nutritional status on the development of infectious diseases such as measles (e.g., Sinha 1977) and noninfectious conditions like diabetes (e.g., Young et al. 1990; Szathmáry 1994). McElroy and Townsend (2009) and Wiley and Allen (2009) provided readable introductions to the many interactions between ecology and health and disease. In addition, Crawford (2003) introduced essential biological characteristics of pathogens in a very engaging manner.

  The history of human disease in both prehistoric and historic times has been a topic of great interest within anthropology for decades, with numerous articles and books dedicated to it. Infectious diseases were identified as an important selective factor in human evolution as early as the middle of the 20th century (Haldane 1957; Motulsky 1960). One of the most influential books on this topic was written not by an anthropologist, but by a historian, William McNeill, who in 1976 published his monumental work, Plagues and Peoples.

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