This document discusses the epidemiological triad of host, agent, and environment as factors that influence disease transmission. It describes different modes of disease transmission including droplet and airborne transmission. It also outlines approaches for disease prevention and control, including eradication of infectious diseases, interrupting transmission, and protecting susceptible hosts through immunization. Emerging and reemerging infectious diseases are discussed.

1. Dr. Amany R.AboEL-Seoud
Prof. of Community Medicine
Zagazig University, EGYPT

2. agent
exit
Mode of
transmission
inlet
host

3. bacteria virus
parasite rickettsia
Protozoa&
fungi

4. CASES CARRIERS
SOIL ANIMAL
RESERVOIR
SOURSE

6. CARRIERS
Timing period exit

8.  DROPLET air borne

13. Ecology
Epidemiological triad
Host
Agent
Environment

14.  Age, sex,
 pregnancy,
 occupation,
 education
 Nutrition
 Socioeconomic status
 Level of immunity: types of immunity:
Inherited & acquired (natural , artificial)

15.  Number
 Virulance
 Pathogenicity

16.  Sanitation of air
 Sanitation of water
 Sanitation of housing
 Sanitation of food
 Sanitation of waste disposal
 Sanitation of animals, rodents control

17.  Sporadic
 Outbreak
 Epidemic: common source / propagated
 Pandemic
 Endemic
 Epizootic

18.  Eradication of infectious diseases
 Elimination or control of reservoir of
infection (man, animal, soil)
 Interruption of mode of transmission
(sanitary environment)
 Protection of susceptible host (immunization)

19.  Primary prevention: to prevent the
occurrence of infection (called also general
prevention).
 Secondary prevention: to prevent the spread
of infection to others, to prevent the
complications among cases (may be called
specific prevention or control measures).
 Tertiary prevention: to prevent further
deterioration of cases, to help complicated
cases to cope with their handicapped
conditions.

20.  Population growth and demographic changes
 Increased travel
 Global climatic change
 Wars, famines and disasters affecting many parts
of the world
 Abuse of drugs and antibiotics
 Microbial adaptation and mutations
 Bioterrorism
 Increased nursing homes, old age institutions
 Deforest and changing natural areas
 Building dams, changing irrigation systems
 Unequal distribution of health services, vaccines,
drugs etc

21.  Examples of emerging infections:
 SARS
 Anthrax
 Hantavirus
 Arenaviruses
 Swine influenza
 Ebola virus
 Examples of reemerging infections:
 Tuberculosis
 Malaria
 AIDS

22.  Air borne
 Food borne
 Contact/ blood borne
 Arthropod borne
 congenital