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.

1. CCOONNCCEEPPTTSS OOFF
DDIISSEEAASSEE

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

5. WWEEBB OOFF CCAAUUSSAATTIIOONN

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

18. RRIISSKK FFAACCTTOORRSS

19. AATT RRIISSKK GGRROOUUPPSS

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