Disease causation
Disease causation – History
- Supernatural theory of disease
- Anger of God
- Punishment by God
- Curse by other people
- Invasion by evil spirit
Germ theory of causation
- In 1860 Louis Pasteur demonstrated presence of bacteria in the air
- In 1873 he proposed the germ theory of disease
- 1877 Robert Koch demonstrated that Anthrax was caused by a bacteria
- But germ theory did not explain everything
- Presence of germs did not always cause disease
- All diseases were not caused by germs
Modern Medicine
- An important concept of Epidemiology is that disease does NOT occur randomly in the population
- The disease occurs in those individuals who are exposed to certain risk factors/or who are vulnerable
- One of the important functions of Epidemiology is to find the cause of disease
Concepts of disease causation
- Epidemiological triad
- Rothman’s Pie
- Multifactorial causation
- Web of causation
Epidemiological triad
- Agent
- Host
- Environment
- Disease is caused by the interaction of all three factors
The triangle of epidemiology
- The triangle of epidemiology shows the interaction and interdependance of agent, host, environment and time
- It is different from epidemiological triad which does not contain time, but contain other three components
Advanced model of the triangle of Epidemiology
- This new model includes all facets of the communicable disease model.
- The term ‘agent’ is replaced by causative factors and this model shows the interaction of : –
- Causative factors
- Group of population and their characteristic
- Environment behaviour, culture, physiological factors, ecological elements
- time.
Agent factors
- Virus, Bacteria, stress, vitamin etc.
- Virulence
- Ability to cause disease depends on the number or amount of agent
Host factors
- Age
- Sex
- Immunity
- Socioeconomic – overcrowding, educational status etc.
- Heredity
- Nutritional status
- Presence of other diseases
Environmental factors
- Climate – temp, humidity etc
- Presence of vectors
- Sanitation
- Availability of health services
Rothman’s Causal Pies
- In case of non-communicable diseases like Cardiovascular disease, Diabetes, Hypertension etc.
- There are many risk factors
- All of them need not be present
- The Epidemiological triad does not explain the causation satisfactorily
- Not all risk factors are necessary to cause disease
- When the required number of risk factors joins it is called Sufficient cause
- If some risk factor is present always, it is called Necessary cause
- Disease prevention can be achieved even by blocking just ONE risk factor
Multifactorial causation
- Suggested by Pettenkofer of Munich
- Tuberculosis is not caused by presence of Mycobacterium tuberculosis alone.
- Contributing factors like overcrowding, malnutrition etc. need to be present
- Coronary heart disease – excess fat intake, smoking, lack of physical exercise, obesity etc.
Web of causation
- Mac Mohan and Pugh
- Web of causation considers all predisposing factors or risk factors and their interaction
- This model is ideally suited in the study of chronic disease, where the disease agent is often not known but is the outcome of interaction of multiple factors.
- The causal web provides a model which shows a variety of possible interventions that could be taken which might reduce the occurrence of disease (e.g. MI)
- The web of causation does not imply that the disease cannot be controlled unless all the multiple causes or chains of causation or at least a number of them are appropriately controlled. This is not the case. Sometimes removal or elimination of just only one link or chain may be sufficient to control disease, provided that link is sufficiently important in the pathogenic process.
- Therefore, in a multifactorial event, individual factors are by no means all of the equal weight.
BEINGS Model Of Disease causation
- Preventable causes of disease
- B: Biological factors and behavioural factors.
- E : Environmental factors.
- I : Immunological factors.
- N : Nutritional factors.
- G: Genetic factors.
- S : Services, social, spiritual factors.
Exam Important
- Web Causation of disease is most appropriate Better for all the related factors associated with causation of disease
- BEINGS Model of disease causation includes Spiritual factors , Social factors & Nutritional factors
- Theory of web of causation was given by Mc Mohan and Pugh
- Germ theory of disease was proposed by Louis Pasteur
- Multifactorial causation of disease theory was proposed by Pettenkofer
- Epidemiological triad includes Environment, Agent & host
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