The document discusses the epidemiological triad, which consists of three essential factors for disease occurrence: agent, host, and environment. It details various types of disease agents, including biological, nutritional, chemical, mechanical, physical, and social agents, as well as host factors like demographics and lifestyle. Finally, it examines environmental factors that contribute to diseases, categorizing them into physical, biological, and physiological environments.

1. Epidemiological triad
SAURABH SINGH TOMAR
ASSIT.PROFESSOR
(COMMUNITY HEALTH NURSING)
E-MAIL-saurabh.singh406@gmail.com

2. Introduction
• For occurrence of disease in men there are
three things are required –
Agent
Host
Environment
• These three factors are referred to as
Epidemiological triad. Disease cannot occur in
the absence of any one of these three factors

3. Epidemiological triad
Agent
Host Environment
1. Biological
2. Nutritional
3. Physical
4. Chemical
5. Mechanical
1. Age
2. Sex
3. Genetic
4. Profession
5. Customs
6. Habits
7. Behaviors
1. Physical
2. Biological
3. Social

4. 1. Agent

5. 1. Agent
• Agent is the first link in the chain of disease
transmission.
• In the development of disease agent is the foremost
factor, it can be living or non living .
• These disease agent have been classified into 5
broad groups
1. Biological agent
2. Nutritional agent
3. Chemical agent
4. Mechanical agent
5. Physical agent
6. Social agent

6. 1. Biological agent
• These are the living agents which are found in
man, animals, insects, soil and air etc.
• These biological agent are poisonous and
spread infections and generate disease.
• Biological agents are –
 VIRUS
 BACTERIA
 PROTOZOVA
 FUNGUS

7. 2. Nutrient agents
• The nutrients are essential for
keeping an individual healthy.
An excess or deficiency of
intake of these nutrients can
result in nutritional deficiency
disorders.
• Proteins, fats, carbohydrate,
vitamins, minerals and water
are the nutrients agents.
• Disorders due to nutrients-
• PEM
• Anemia
• Goiter
• Obesity and
• Vitamins deficiencies.

9. 3.Chemical agent
• The chemical agents which affect the human health are
two type
1. Endogenous chemical agent.
2. Exogenous chemical agent.
1. Endogenous chemical agent -The chemical agent
which are produced and present in human body called
Endogenous chemical agents. These chemical can excess
or less and result in illness.
Eg –
• Serum Bilirubin( excess of Bilubirin result in jaundice)
• Urea (Ureamia)
• Ketones (Ketosis)
• Uric acid(Gout)
• Calcium carbonate(Kidney stones)

10. 2. Exogenous chemical agent.- The chemical agents
which are present in outside in the human body is
called as Exogenous chemical agent.
Eg-
Gases
Metals
Dust
Smoke
Fumes
Insecticides
Allergens etc.
• These agent may be acquired
by inhalation, ingestion, or inoculation.

11. 4.Mechanical agent
• Exposure to chronic friction and other
Mechanical forces may result in crushing
tearing, dislocation, injuries, fractures and
even death.

12. 5. Physical agents
• Exposure to excessive heat, cold, humidity,
pressure, radiation, electricity, sound etc, may
cause the various disease.

13. 6. Social agent
• Social agent like Poverty, Illiteracy, Prostitution
Population explosion, Unhealthy life style, Smoking,
Drinking, Drugs and other addictions, Social isolation,
are also responsible for many disease.

14. 2. Host factors

15. 2. Host factors
• 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 factors may classified as –
1. Demographic characteristics
2. Biological characteristics
3. Social and economic characteristics
4. Life style factors

16. The Host Factors May Classified as –
4.Life style factors
3.Social and Economic
characteristics
2.Biological
characteristics
1.Demographic
characteristics
Age, sex etc
Genetic factor, biochemical
level of blood(cholesterol),blood
groups and enzymes.
Socio economic status,
Education, Occupation, Stress,
Marital status, Housing etc.
Personality traits, Living habits,
Nutrition, Physical exercise, Use
of alcohol, Drugs and Smoking,
Behavioral patterns etc

17. 1. Demographic factors
• This include individuals age sex, etc. some
disease are common in childhood(Eg-Measles,
PEM,) and some disease are more prevalent in
old age(enlargment of prostate gland, cataract,
and osteoporosis)
• Similarly there are certain disease which affect
women more and other are found in men only.

18. 2. Biological factors
• Some disease are common in some specific
individual only.
• Eg – Disease depending on the structure of
genes or genetic disease, congenital disease,
mental disorder, blood disease, diabetes and
hypertension.

19. 3. Socioeconomic factors
• Onset of the disease is also affected by the
individuals economic and social status,
education, habits, marital condition and
profession etc.

20. 4. Life style
• Customs and rituals, moral values, habits,
nutrition, physical labour, consumption of
alcohol, drug addiction, smoking behavior and
personality etc.
• Eg – people those who are addicted to drugs or
alcohol are more likely to fall ill.

21. Environmental factors

22. Environmental factors
• Study of disease is a study of man and his
environment. It has been proved that polluted
environment is responsible for many diseases.
• Environment factors are classified into three
groups
1. Physical environment
2. Biological environment
3. Physiological environment

23. 1. Physical environment
• Air, House, Season, Water, Land, Temperature, Light,
Noise, Radiation, Disposal of body waste, (faeces and
urine),Disposal of refuse etc, are the physical factors
which affects the environment.

24. 2. Biological environment
• This include the Organisms(animals, insects,
rodents,) which can cause disease.

25. 3. Physiological environment
• Customs faith, education, standards of living
culture, tension, and breaking up with family
etc, are related to onset of disease either
directly or indirectly.