Disease Concepts and ProcessDr (Col) Harinder S Ratti (M) +91 9868260109ratti2@gmail.com

Likely Questions• Long Q

– Natural History of Disease

• Short notes– Germ theory of Disease– Epidemiological triad– Multifactorial causation– Web of causation

Disease• Definition

– A condition in which •body health is impaired, •a departure from a state of Health •an alteration of human body interrupting the functioning of vital organs

– Ecological definition•Maladjustment of human being to the environment

– Sociological Definition• Its is social phenomenon in all societies based on cultural forces prevalent in

the society• WHO Definition – of Health Not disease

– Spectrum of Disease• In apparent (Sub clinical ) to Severe manifestations

Terms– Disease - Physiological

•‘Dis’ –ease– Illness - Subjective

•Presence of specific disease•Individual perceptions and behavior in response to that disease

•Impact of the disease on the psychological environment

– Sickness - Functional•State of Social dysfunction

A Clinician sees a person who is Ill, rather than disease, which he diagnose and treat

It is possible to be Diseased without being Ill. It is possible to be Ill without being physically impaired

Concept of Disease• Supernatural theory of disease causation

• The theory of humors• Concept of contagion• Miasmatic theory• Theory of Disease• Theory of spontaneous generation

Germ Theory of Disease – Louis Pasteur (-1995 – 1922)Emphasis shifted from empirical causes to microbes as sole cause of diseaseOne to One relationship of Cause - Effect

Multifactorial Causation – Current concept

Epidemiological Triad

• The Germ theory has many limitations

• Need for a broader concept

Environmental Factors

Determinants of Disease

Determinants of DiseaseHost factorsThe physical and chemical constitution of the host acts as a defensive mechanism while these in turn are affected by genetic and environmental influences such as diet, climate, stress, exercise, fatigue and existing or previous disease conditions. 

Determinants of DiseaseEtiological AgentPhysical –

mechanical injuries trauma, thermal, radiation, noise (psychological stress)light, etc.

Chemical organic/inorganic forms, gases

Nutritional metabolic,primary/secondary nutritional deficiencies, hormonal imbalances, etc.

Biological – all living organisms that cause disease or infection - bacteria, virus, rickettsia, protozoa, fungi, etc. 

Multifactorial Causation

• Biological • Physical• Chemical • Nutritional

• Biological  

Web of CausationConcept Promoted by MacMohan and Pugh1970 – Epidemiologic principles and Methods

Causal web provides a visual model which shows variety of possible interventions that can be undertaken to reduce occurrence of disease

-Ideal for Chronic Diseases- Disease Agent unknown, Outcome is a interaction of multiple factors- Considers all pre disposing factors and their complex inter-

relationships with each other : eg : AMI

Control NOT necessarily on break of any single link in chain

Web of Causation

Disease ProcessWhat does "disease process" mean?

• "disease process" refers to the natural progression of a disease, its symptoms and treatment, from first diagnosis to its final outcome, death.

The infectious disease process is defined as the interaction

between the pathogenic microorganism, the

environment, and the host. The process may be thought of as a circular chain with six links.

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