CONCEPT OF DISEASE CAUSATION

Disease is a dynamic process just opposite to health. It denotes disharmony and deviation from the normal functioning of various body system. Wellness and illness are the two end point of health and disease.

The concept of disease causation differed from time to time with progress of civilization. It changes from supernatural causes during primitive time period to multifactorial causes during modern time. Importance is to identify public health measures to prevent and control diseases.

THEORIES AND MODELS OF DISEASE CAUSATION

•        Before the discovery of microorganism several theories explaining the causes of disease put forward time to time.

•        Earliest attempt in religious era (2000 BC- 600 BC) – Disease caused by divine power as punishment from sin and bad deeds or considered as a fate referred as ‘Supernatural theory’. 

•        Other theory, the disease was caused due to various physical forces such as miasma or mists referred as ‘Miasmatic theory’. 

•        400 BC rudimentary environmental theory was put forward by Hippocrates, believed that the disease was caused by harmful substances in the environment. 

•        With discovery of microorganism, the bacteriological era commenced in late 1870, which was the turning point in disease causation.  Thus earliest theories were discarded and germ theory was put forwarded.

                 

                1.    THE GERM THEORY

It became popular during 19^th and early part of 20^th century. This theory attribute microorganisms as the only cause of disease. According to this theory one specific microorganism (causative agent) responsible for every diseases. Refers to as ‘one to one relationship between causative agent and disease’, also known as ‘Single Cause Theory’.

This theory was limited to infectious diseases only. This theory was further  criticized due to identification of other specific agents causing health problem.  E.g.:- Vitamin C deficiency cause scurvy

2.    EPIDEMIOLOGICAL TRIAD

 The Germ theory has many limitations, it was experienced that everyone exposed to disease agent did not cause the disease. Not only the causative agent but also other factors related to man and environment contribute to the occurrence of disease. This lead to theory of epidemiological triad (Ecological model).

 

According to this model there are 3 elements – agent, host and environment, which is responsible for disease causation.

• Agent – Considered to be the primary factor (bacteria, virus), without which a particular disease did not occur.

•     Host – refers to human being

•     Environment – include all that external to the host and agent

 

 Disease will occur only when the agent is strong and enters the host through right channel sufficient amount, the host is susceptible and when environmental conditions facilitate interaction of host and agent.

 

 3.    MULTIFACTORIAL CAUSATION THEORY

The epidemiological triad was applicable in communicable diseases only.  It help to understand different factors causing communicable diseases.  However this is not applicable in NCD and other mental disorders. Because these are not linked with any infectious organism. These are caused by multiple factors, Eg:- CAD due to smoking, ingestion of food containing high level of cholesterol, lack of exercise, mental and emotional stress.  This lead to theory of multifactorial causation. 

      

This model helps epidemiologist to understand various associated causative factors and plan prevention and control. It also found that many observed effects e.g.:- air pollution, smoking, and radiation can cause lung cancer, emphysema and bronchitis.

4.    WEB OF CAUSATION 

This epidemiological concept of disease aetiology was put forward by Mac Mohan and Pugh.  According to this disease is never depend upon single isolated cause. It suggest that there are cluster of causes and combination of effect related to each other and need to study for finding possible intervention. This model is particularly applicable to chronic diseases where the causative agent is unknown and which are due to interaction of multiple factors. E.g.:- CVD, cancer

  

 

5.    DEVERS EPIDEMIOLOGICAL MODEL      

       This model composed of four major categories of factors,

•        Human biology

•        Life style

•        Environment

•        health system

All these factors influence health status positively or negatively.

ü Human biological factors

 Epidemiological triad and genetic inheritance, complex physiological systems factors related to maturation and ageing.

ü Life style factors include daily living activities, customs, traditions, health habits, etc..

ü Environmental factors include physical, biological, social and spiritual components.

ü Health care system factors include availability, accessibility, adequacy and use of health care services at all levels.

 

6.    SPECTRUM OF DISEASE

Spectrum of disease is the graphical representation of variations in the manifestations of disease. At one end of the disease spectrum are subclinical infection which are not ordinarily identified and at the other end are fatal illness. In the middle of the spectrum lie illness ranging in severity from mild to severe.

  

7.    ICEBERG OF DISEASE

To this the disease can be closely related with an iceberg. The floating tip of the iceberg represents what the physician sees ie, clinical cases. The vast submerge portion of the iceberg represents the hidden mass of the disease ie, latent, unapparent, presymptomatic and undiagnosed cases and carriers in the community. 

 

Referance:

1. Sharon Mantik Lewis, Heitkemper MM, Shannon Ruff Dirksen. Medical surgical nursing. St. Louis, Mo. ; London: Mosby; 2004.

2. Hinkle JL, Cheever KH. Brunner & Suddarth’s textbook of medical-surgical nursing. 14th ed. Philadelphia Wolters Kluwer Health, Lippincott Williams & Wilkins; 2018.