Concepts of disease
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This document defines key concepts related to disease, including definitions of disease, illness, and sickness. It discusses theories of causation, including the germ theory and epidemiological triad. It also outlines the natural history of disease, including prepathogenesis, pathogenesis, and outcome phases. During these phases, interactions between agents, hosts, and environmental factors can initiate and perpetuate disease processes. The document also examines factors related to agents, hosts, and environments that influence disease and identifies risk factors and risk groups.
Concepts of disease
- 2. DDEEFFIINNIITTIIOONNSS • 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.
- 3. CCOONNCCEEPPTT OOFF CCAAUUSSAATTIIOONN • Germ theory of disease – bad air to microbes one to one relationship-- Disease agent ---- Man ----Disease Limitations- ex TB,RH fever • Epidemiological triad
- 4. MMUULLTTIIFFAACCTTOORRIIAALL CCAAUUSSAATTIIOONN • 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
- 6. NNAATTUURRAALL HHIISSTTOORRYY OOFF DDIISSEEAASSEE • Prepathogenesis phase (process in environment) • Pathogenesis phase (process in man) Agent factors Host factors Environmental factors Risk factors and risk groups
- 7. PPRREEPPAATTHHOOGGEENNEESSIISS PPHHAASSEE • Man in the midst of disease/ Man exposed to the risk of disease • Interaction between H A E initiate the disease process in man
- 8. PPAATTHHOOGGEENNEESSIISS PPHHAASSEE • 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
- 9. NNAATTUURRAALL HHIISSTTOORRYY OOFF DDIISSEEAASSEE
- 10. AAGGEENNTT FFAACCTTOORRSS • 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
- 11. AAGGEENNTT FFAACCTTOORRSS-- CCOONNTT’’DD • 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
- 12. HHOOSSTT FFAACCTTOORRSS • 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.
- 13. EENNVVIIRROONNMMEENNTTAALL FFAACCTTOORRSS • Macro environment “all that which is external to the individual human host, living and non-living, and with which he is in constant interaction”..
- 14. PPHHYYSSIICCAALL EENNVVIIRROONNMMEENNTT 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.
- 15. BBIIOOLLOOGGIICCAALL EENNVVIIRROONNMMEENNTT 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.
- 16. PPSSYYCCHHOOSSOOCCIIAALL EENNVVIIRROONNMMEENNTT “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.
- 17. RRIISSKK FFAACCTTOORRSS • 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
- 20. SSPPEECCTTRRUUMM OOFF DDIISSEEAASSEE • “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
- 21. IICCEE BBEERRGG OOFF DDIISSEEAASSEE