CONCEPTS OF CONCEPTS OF DISEASEDISEASE

DEFINITIONSDEFINITIONS• Webster – a condition in which body health is

impaired, a departure from a state of health, an alteration of the human body interrupting the performance of vital functions

• Simplest-opposite of health• WHO not defined• Illness- is a subjective state of the person who feels

aware of not being well• Disease is a physiological/psychological dysfunction• Sickness is a state of social dysfunction- a role that

the individual assumes when ill.

CONCEPT OF CONCEPT OF CAUSATIONCAUSATION

• Germ theory of disease – bad air to microbes

one to one relationship-- Disease agent ---- Man ----Disease

Limitations- ex TB,RH fever• Epidemiological triad

MULTIFACTORIAL MULTIFACTORIAL CAUSATIONCAUSATION

• Stresses multiplicity of interactions between host, agent and environment

Social, economic, cultural, genetic, psychological factors

ex: coronary heart disease, TB• Web of causation- ideally suited for

chronic disease , where the agent is unknown, but is the outcome of interaction of multiple factors

WEB OF CAUSATIONWEB OF CAUSATION

NATURAL HISTORY OF NATURAL HISTORY OF DISEASEDISEASE

• Prepathogenesis phase (process in environment)

• Pathogenesis phase (process in man)

Agent factors

Host factors

Environmental factors

Risk factors and risk groups

PREPATHOGENESIS PREPATHOGENESIS PHASEPHASE

• Man in the midst of disease/ Man exposed to the risk of disease

• Interaction between H A E initiate the disease process in man

PATHOGENESIS PHASEPATHOGENESIS PHASE

• Entry of disease agent into host

• Agent multiplies—induce chances– period of incubation --- early pathogenesis --- late pathogenesis--- final outcome

• Presymptomatic phase- CHD the early pathogenesis phase is less dramatic

• Clinical/subclinical

• Typical /atypical

• Carrier with / without having clinical disease

NATURAL HISTORY OF NATURAL HISTORY OF DISEASEDISEASE

AGENT FACTORSAGENT FACTORS• Agent is defined as a substance, living or non

living, or a force, tangible/intangible, the excessive presence or a relative lack of which may initiate or perpetuate a disease process.

• Biological- living agents- exhibit host related biological properties, viruses, fungi

• Infectivity

• Pathogencity

• virulence

AGENT FACTORS- AGENT FACTORS- CONT’DCONT’D

• Nutrient agents - proteins, vitamins

• Physical agents - heat, cold, radiation

• Chemical Endogenous, exogenous

• Mechanical

• Absence or insufficiency or excess of a factor necessary to health - hormones

• Social agents

HOST FACTORSHOST FACTORS• Demographic characteristics -age, sex,

ethnicity.

• Biological characteristic - genetic factors, blood pressure, forced expiratory ventilation. Blood groups, enzymes. Etc.

• Social and economic characteristic - education, occupation, stress, marital status, housing, etc.

• Life style factors personality traits, living habits, nutrition, physical exercise, use of alcohol, drugs and smoking, behavioral patterns, etc.

ENVIRONMENTAL ENVIRONMENTAL FACTORSFACTORS

• Macro environment “all that which is

external to the individual human host,

living and non-living, and with which he is

in constant interaction”..

PHYSICAL PHYSICAL ENVIRONMENTENVIRONMENT

The term “Physical environment” is applied to non-living things and physical factors (e.g., air, water, soil, housing, climate, geography, heat, light. Noise, debris, radiation, etc) with which man is in constant interaction.

BIOLOGICAL BIOLOGICAL ENVIRONMENTENVIRONMENT

The biological environment is the universe of living things which surrounds man, including man himself. The living things are the viruses and other microbial agents, insects, rodents, animals and plants.

PSYCHOSOCIAL PSYCHOSOCIAL ENVIRONMENTENVIRONMENT

“Those factors affecting personal health, health care and community well-being that stem from the psychosocial make-up of individuals and the structure and functions of social groups”. They include cultural values, customs, habits, beliefs, attitudes, morals, religion, education, lifestyles, community life, health services, social and political organization.

RISK FACTORSRISK FACTORS• An attribute or exposure that is significantly associated

with the development of the disease• A determinant that can be modified by intervention

thereby reducing the possibility of occurrence of disease or other specified outcomes

• Additive or synergistic• Truly causative• Contributory• Predictive in statistical sense• Modifiable/ unmodifiable• Collective community risks- expression of need

RISK FACTORSRISK FACTORS

AT RISK GROUPSAT RISK GROUPS

SPECTRUM OF SPECTRUM OF DISEASEDISEASE

• “Gradient of infection” in infectious disease

• Graphic representation of variations in the manifestations of disease

• Sub clinical cases ------mild illness---- severe illness------ fatal illness

• Reflect individuals different state of immunity and receptivity

ICE BERG OF DISEASEICE BERG OF DISEASE