3. Causation/Cause
In epidemiology a cause can be considered to
be something that alter the frequency of
disease, health and production status or
associated factors in population
4. Causation models
Many models are present in epidemiology but the most common are
1. Epidemiological triad
2. Wheel or pie model
3. Web model
4. The sufficient cause and component causes model (Rothman’s
component cause model)
5. Epidemiological triad
Traditional model of infectious disease causation
It has three components
1. An external agent
2. Susceptible host
3. Environmental factors
These components interrelate in variety of complex ways to produce
disease and alter production
6.
7. Agent factors
1. infectious agents- agent might be Mos (virus, bacteria, parasites, prions). Generally these
agents must be present for the disease to occur as an essential causal factor.
2. Nutritive- excessive or deficiencies (cholesterol, vitamins and minerals)
3. chemical agents- (carbon monoxide, drugs and medication)
4. Physical agents- (ionizing radiation, non-ionizing radiation)
8. Agent factors
Living organism: adaptability, host range, virulence, pathogenicity, dose ID50, LD50
Chemical agents (toxins n pollutants): toxicity dose, penetrability, stability, half life
Physical agents (radiation, sounds, winds, floods, droughts, soil): composition, magnitude,
exposure time
9. Host factors
Host factors are intrinsic factors that influence an individual’s exposure, susceptibility or
response to causative agent.
Host factors that affect an individuals risk of exposure to an agent: age, race, breed, strain,
purpose of domestication, feed and feeding habits, breeding practices, sociological status
etc.
Host factors which affect the susceptibility and response to an agent: genetic composition,
nutritional and immunogenic status, anatomic structure, presence of other diseases and
medications, purpose and use of domestication, method of rearing and husbandry
practices and psychological makeup.
10. Environmental factors
These are the extrinsic factors which affect the agent as well as host and
opportunity for exposure.
Environmental factors include:
1. Physical factors such as geology and climate
2. Biological factors such as insects that transmit an agent
3. Socioeconomic factors such as crowding, sanitation and availability of
health services,
11. Web of causation
It is devised to address chronic disease and can also be applied to
communicable diseases due to multifactorial/multi-etiological nature of
causation in many diseases.
Silent features
1. There is no single cause
2. Causes of diseases are interacting in various ways
3. Illustrate the interconnections of possible causes
4. Here the disease is usually well-defined from clinical point of view but the
etiological perspective is more complex
14. The wheel of disease causation
Mausner and Kramer, 1985
The wheel of causation de-emphasizes the agent as the sole cause of disease
It emphasizes the interplay of physical, biological and social environments
It also brings genetics into the mix
A disease model which discriminates between “necessary” and “sufficient”
factors
15. Necessary and sufficient causes
A necessary cause is a causal factor whose presence is required for the
occurrence of the effect. If disease does not develop without the factor being
present, then we term the causative factor “necessary”
Sufficient cause is “a minimum set of conditions, factors or events needed to
produce a given outcome”.
The factors or conditions that form a sufficient cause are called component
causes
17. Rothman’s component causes and
causal pies model
Rothman’s model has emphasized that the causes of diseases comprise a collection of factors.
These factors represent a pieces of pie, the whole pie(combinations of factors) is the sufficient
cause for the disease.
May be several pies for a disease or syndrome
It shows that disease may have more than one sufficient cause, with each sufficient cause being
composed of several factors
