L4.2.1: Models of Disease Causation

• Models of Disease Causation

  1. Epidemiologic Triad

  2. Infectious DIsease Model

  3. Causal Pies
• Epidemiologic Triad

  ● Traditional model for infectious diseases

  ● Proposed by John Wade Frost
• Epidemiologic Triad

  
  

  DYNAMIC INTERACTIVE ELEMENTS

  a. Host — humans, animals, etc.

  b. Agent — CA (causative agents), such as, mycobacterium tuberculosis for TB (for animals: mycobacterium bovis; past bacteria when mode of transmission is through intake of unpasteurized milk)

  c. Environment — habitat of the microorganism (ex: dirty rivers, soil–for tetanus, amoeba–heat-loving, armpits)
• Epidemiologic Triad

  
  

  DYNAMIC INTERACTIVE ELEMENTS

  ○ The traditional agent for infectious diseases

  ○ Consists of an external agent, a susceptible host, and an environment that brings the host and agent together which results in disease through the interaction of the three dynamic elements.

  ○ Proposed by John Wade Frost (1928)
• Epidemiologic Triad

  
  

  ● Agent

  ○ An infectious microorganism or pathogen which exposure to an organism will result in a disease through a variety of factors

  ○ Can also be attributed as:

  ■ Physical agents

  ■ Chemical agents

  ■ Nutrient Agents

  ■ Mechanical agents

  ■ Social agents
• Epidemiologic Triad

  
  

  ● Host

  
  

  ○ Refers to the human who gets the disease.

  ○ Exposure, susceptibility, or response to a causative agent is influenced by risk factors.

  ○ Can either be influenced by:

  ■ Demographic characteristics

  ■ Biological characteristics

  ■ Socioeconomic characteristics
• Epidemiologic Triad

  ● Environment

  ○ Refers to the extrinsic factors that affect the agent and the opportunity for exposure to the host.

  ○ Factors that may affect include:

  ■ Physical environment

  ■ Biological environment

  ■ Social environment
• Infectious DIsease Model

  ● Opportunistic Infection

  ○ If low in antibodies, if host is weak

  ○ Agent is changed to pathogen

  ■ Since not all microorganisms are disease-causing
• Causal Pies

  ● Accounts to multifactorial nature of causation of a particular disease

  ● Can be used for non-infectious diseases

  ● Pie as a representation of the different contributing factors to the development of a disease

  ● Developed by Kenneth J. Rothman (1976)
• Causal Pies

  TYPES OF CAUSES

  • Component Cause
  • Necessary Cause
  • Sufficient Cause
• Causal Pies

  Component Cause

  ● Contributes to an individual factor that contributes to cause disease
• Causal Pies

  Necessary Cause

  ● Component that appears in every pie or pathway wherein without it, disease does not occur
• Causal Pies

  Sufficient Cause

  ● Involves a complete pie

  ● Causal pathway to development of disease

  ● Can be various causes to form a disease