EVENTS IN NATURAL HISTORY OF DISEASE 1.Pre-Pathogenesis phase •This period is preliminary to the onset of disease. •Disease agent not entered man but factor which favour its interaction with the human host are always existing in the environment. 2.Pathogenesis phase •This period begins with the entry of disease agent in the susceptible human host. FACTORS OF EPIDEMIOLOGICAL TRAID 1.Agent Factor: - •First link in the chain of disease transmission. •Agent defined as substances living or non-living or a force the excessive presence or relative lack of which may initiate or perpetuate a disease process. •A disease may have single agent a number or a complex of two or more agent. •Disease agents are: - a)Biological agent: •These are living agent of disease. •This agent exhibits certain “host” related biological properties such as, i.Infectivity – oability of infectious agent to invade and multiply. ii.Pathogenicity – ability to induce clinically aperantt illness. iii.Virulence – opreparation of clinical cases resulting in severe clinical manifestation b)Nutrient agent: •These are proteins, fat, carbohydrate, vitamins, minerals and water. •Any excess or deficiency results in nutritional disorder. c)Physical agent: •Exposure to excessive heat, cold, humidity, pressure, radiation, electricity, sound may result in illness d)Chemical agent: i.Endogenous – Chemical produced in the body due to derangement of function serum bilirubin. ii. Exogenous – arising outside of human host. E.g.- allergen, metals, dust, etc e)Mechanical agent: •Exposure to chronic friction and other mechanical forces may result in crushing, tearing, sprains, dislocation or even death. f)Absence or insufficiency or excess of a factor necessary to health: •Chemical factor - hormones. E.g. – insulin •Nutrient factor •Lack of structure e.g.- thymus •Lack of parts of structure e.g. – cardiac defect •Chromosomal factor e.g. – magnolia •Immunological factor g)Social agent: •These are poverty, smoking, abuse of drugs and alcohol 2.Host Factor (Intrinsic): - •It plays a major role in determining the outcome of an individual’s exposure to infection. e.g. – tuberculosis •Human host is referred to soil to the disease. •Host factors are – i.Demographic characteristics – age, sex, ethnicity ii.Biological characteristics – genetic factors, biochemical levels of blood. iii.Social and economic characteristics – socio-economic status, education, occupation, stress, housing, etc iv.Lifestyle factor – personality traits, living habits, nutrition, physical exercise 3.Environmental Factor (Extrinsic): - •Environment is the reservoir for the agents of disease. •It helps in transmission of agents to host bringing about their contact and interaction. •The environment of man is of two types: - External Environment – oIt is all that which is external to the individual human host. Macro-environment is another term used to denote external environment. Micro-environment is the term used to denote one’

1. EPIDEMIOLOGICAL TRIAD

2. INTRODUCTION
EVENTS IN NATURAL HISTORY OF DISEASE
FACTORS OF EPIDEMIOLOGICAL TRAID
AGENT FACTOR
HOST FACTOR (INTRINSIC)
ENVIROMENTAL FACTOR (EXTRINSIC)
CONCLUSION
REFERENCES
CONTENT

3. EPIDEMIOLOGICAL TRIAD
 DEFENITION
• The occurrence and manifestation of any disease either
communicable or non communicable are determined by the
agent, the host and the environment. This together constitute
epidemiological triad.

4. FACTORS OF EPIDEMIOLOGICAL
TRIAD
Agent Host
Environment

5. AGENT FACTOR

6. AGENT FACTOR
 First link in the chain of disease.
 In the development of disease, agent is the foremost factor, it can
be living or non-living.

7. AGENT FACTOR
 These disease agents classified into 6 broad groups:
i. Biological agent e.g. Bacteria, Virus.
ii. Nutritional agent e.g. Carbohydrate, Fats and Vitamins.
iii. Chemical agent e.g. Allergen, Metal, Serum bilirubin.
iv. Mechanical agent e.g. Tearing, Sprains, Dislocation.
v. Physical agent e.g. Electricity, Sound, Radiation.
vi. Social agent e.g. Smoking, Abuse of drug, Alcohol

8. HOST FACTOR
• Host factor is the human body where the disease agent
stay, grow and multiply to produce illness.
• In epidemiology terminology the human host is referred
to as soil and the disease agent as seed.
The host factor may be classified as –
i. Demographic e.g.- age, sex, ethnicity
ii. Biological e.g.- genetic factor
iii. Social and economic e.g.- education, occupation
iv. Life style factors e.g.- personality traits, living habits

9. ENVIRONMENTAL
FACTORS

10. ENVIRONMENTAL FACTORS
• Study of disease is a study of man and his environment.
It has been proved that environment is responsible for
many diseases.
Environment factors are classified into three groups:-
• Physical environment
• Biological environment
• Physiological environment

11. CONCLUSION
In conclusion, epidemiology is a vital discipline that
provides critical insights into disease patterns, risk factors,
and public health interventions. By studying the
distribution and determinants of diseases, epidemiologists
contribute to the development of effective strategies to
prevent, control, and manage diseases, ultimately
improving the health and well-being of populations
around the world.

12. 1. K. Park. Park's Textbook of Preventive and Social
Medicine. 26th Edition, Madhya Pradesh: M/s
Banarsidas Bhanot Publishers; 2021.
2. Soben Peter. Essential of Public Health Dentistry
(Community Dentistry). 7th Edition, New Delhi: Arya
Medi Publishing House PVT. Ltd.; 2022
REFERENCE

13. THANK
YOU