This document outlines key concepts in epidemiology of infectious diseases. It defines important terminology like reservoirs, transmission modes, immunization, and surveillance. It describes the dynamics of disease transmission including the chain of infection from reservoir to susceptible host. Human, animal and environmental reservoirs are described. Modes of transmission can be direct like contact or indirect like vector-borne. Host defenses include active immunity from vaccines/infection and passive immunity from maternal antibodies. National immunization schedules aim to provide protection against vaccine-preventable diseases.

1. EPIDEMIOLOGY OF
INFECTIOUS DISEASES
GUIDE: Dr. Sachin Patil Sir
PRESENTED BY: M. G. Revathi

2. CONTENTS:
1. 1. INTRODUCTION
2. 2. TERMINOLOGY AND DEFINITIONS
3. 3. DYNAMICS OF DISEASE TRANSMISSION
(a) Human Reservoir
(b) Animal Reservoir
(c) Reservoir in Non-Living
4. 4. MODES OF TRANSMISSION
1. (a) Direct Transmission
2. (b) Indirect Transmission
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3. CONTENTS (Contd..):
1. 5. SUSCEPTIBLE HOST
2. 6. HOST DEFENCES
1. (a) Active Immunity
2. (b) Passive Immunity
3. 7. IMMUNIZING AGENTS
4. 8. NATIONAL IMMUNIZATION SCHEDULE
5. 9. REFERENCES
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4. 3

5. According to the World Health Organization’s
(WHO 2010)
1. Annual estimates, there are globally
a. 300 to 500 million ――― Malaria,
b. 333 million ―――――― Sexually transmitted diseases,
c. 33 million ―――――― HIV/AIDS,
d. 14 million ―――――― Tuberculosis,
e. 3–5 million ―――――― Cholera.
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6. INTRODUCTION
THE GLOBAL BURDEN OF INFECTIOUS DISEASES
1. Infectious diseases ---- major cause ---- human suffering ----
morbidity and mortality ---- human history.
2. Morbidity ---- infectious diseases ---- very common ----
progress ---- recent decades.
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7. The Importance of Infectious Disease
Epidemiology for Prevention
“Epidemiology rationale prevention and control
of diseases.”
To prevent diseases, it is important to understand the
causative agents, risk factors, and circumstances that
lead to a specific disease.
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8. TERMINOLOGY
&
DEFINITIONS

9. INFECTION:
1. LEVELS OF INFECTION:
Colonization Infection (S.Aureus in skin
and Nasopharynx)
Subclinical or In-apparent Infection (Polio)
Latent Infection (Virus of Herpes Simplex)
Manifest or Clinical Infection
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Entry
Development/Multiplication
Illness/Asymptomatic

10. CONTAMINATION:
1. Infectious agent on a body surface,
2. clothes, beddings, toys, surgical
3. instruments or dressings.
4. Substances ------- water, food and milk.
5. Contamination Carrier
6. on body state
Pollution is distinct from Contamination.
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11. INFESTATION:
1. Lodgement, development and reproduction
2. of Arthropods on the surface of the body or clothing.
3. E.g.,: Lice, Itch mite.
4. Invasion of the gut by Parasitic worms.
5. E.g.,: Ascaris Lumbrocoides, Pinworms, Tapeworms, Hookworms,
etc.
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12. HOST:
1. Affords subsistence to an infectious agent under natural
conditions.
Includes: human, animals, birds, arthropods etc.
1. Obligate host
2. Definitive host
3. Intermediate host
4. Transport host
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13. INFECTIOUS DISEASE:
1. Disease due to an infectious agent.
1. Contagious
2. Non-contagious
All infections and infestations Communicable diseases
1. CONTAGIOUS DISEASE:
2. Disease transmitted through contact.
3. E.g., Scabies, STD, Leprosy.
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14. COMMUNICABLE DISEASE:
Infectious agent
or toxic products
1. Directly Indirectly
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Infected person/
Animal/ Reservoir
Susceptible host
Illness/
Disease

15. ENDEMIC:
Greek word: EN = In
1. DEMOS = People
A disease that is constantly present in the population of a
particular geographic area, but involves a relative few individuals.
E.g.,: Malaria, Tuberculosis, Chickenpox, etc.
Hyperendemic high levels of disease in all age groups.
Holoendemic highly prevalent in the early ages of life.
favorable
conditions
*present in a community at all times but in low frequency.*
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ENDEMIC EPIDEMIC

16. 14
EPIDEMIC:
Greek word: EPI = Upon
1. DEMOS = People
A situation where a disease spreads rapidly to a large number of
people in a given population over a short time period.
E.g.,: Small pox, H1N1, black plaque, etc.
usual frequency of the disease in the same
EPIDEMICITY area, among the specified population, at the
same season of the year.
“a temporary prevalence of a disease.”

17. PANDEMIC:
Greek word: PAN = All
DEMOS = People
crossing
international boundaries
Effects large population.
Occurs over a wide area.
Characteristics of the
infectious agent
“prevalent throughout an entire country, continent, or the whole world.”
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PANDEMIC
EPIDEMIC
• able to infect humans
• cause disease
• able to spread from
human to human

18. 16

19. SPORADIC:
a. Sporadic = Scattered about.
Cases occur ---------- irregularly.
haphazardly.
infrequently.
*Sporadic may be the starting point of an epidemic.*
Many zoonotic diseases ------- sporadic transmission to man.
EXOTIC:
# Imported into a country in which they do not occur usually.
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20. ZOONOSES:
Infectious disease transmissible under natural condition from
vertebrate animals to man.
1. Epizootic
2. Enzootic
E.g.,: Rabies, Plaque, Bovine
tuberculosis, Anthrax, etc.
a) Anthropozoonoses
b) Zooanthroponoses
c) Amphixenoses
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21. EPIZOOTIC:
1. Outbreak (epidemic) of disease in an animal.
2. E.g.,: Anthrax, Brucellosis, Rabies, etc.
ENZOOTIC:
1. Endemic occurring in animals.
2. E.g.,: Anthrax, Tick typhus, Bovine TB, etc.
EPORNITHIC:
1. Outbreak (epidemic) of disease in a bird population.
2. E.g.,: West Nile virus, etc.
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22. NOSOCOMIAL INFECTION:
1. Spanish word…….NOSOCOMION = Hospital.
Infection acquired by a patient during any health care or
hospital stay.
Denotes a new disorder.
Includes infections acquired in the hospital but appearing after
the discharge, and also such infections among the staff.
Examples: Surgical wounds, Hepatitis B and Urinary Tract
Infections etc.
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23. OPPORTUNISTIC INFECTION:
Infections that are more severe in people with weakened immunity
than in people with healthy immune systems.
People with weakened immune systems
include people living with HIV.
Some opportunistic infections include:
candidiasis, tuberculosis, salmonella
infection, toxoplasmosis.
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24. IATROGENIC INFECTION:
Greek IATROS = healer or physician
1. GENESIS = birth or origin
• An unintended adverse patient outcome due to any
therapeutic, diagnostic and prophylactic intervention not
considered natural in the course of a disease.
Example:
Reaction to penicillin and
immunizing agents,
Childhood leukemia due to
prenatal X-rays, etc…..
*Doctor-generated diseases.*
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25. SURVEILLANCE:
Continuous analysis
Interpretation & Systematically collected data.
Feedback
RATIONALE
Investigative and control measures
Include: Mortality and morbidity
reports, hospital records,
lab diagnosis, outbreak
reports, sickness absence
reports, changes in disease agents, etc.
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26. ERADICATION:
Termination ----- all transmission of infection ----- Extermination
of infectious agent ----- surveillance and containment.
“ALL – OR – NONE”
The only disease eradicated Small pox
Diseases amenable to eradication Measles
Diphtheria
Polio
Guinea worm
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27. DYNAMICS OF
DISEASE
TRANSMISSION

28. DYNAMICS OF DISEASE TRANSMISSION
COMMUNICABLE DISEASE
Reservoir or Source Susceptible host
SOURCE: Person/Animal/Arthropod/Soil/Substance
Infectious
agent
HOST
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29. CHAIN OF INFECTION:
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30. DYNAMICS OF DISEASE TRANSMISSION
(CONTD…)
RESERVOIR: Natural habitat of the causative agent (lives,
multiplies, depends primarily for survival).
Reservoir Source [Not Always]
E.g.: Hookworm infection.
Reservoir ------ Man
Source --------- Soil
Reservoir Source
E.g.: Tetanus.
Reservoir Soil
Source
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31. DYNAMICS OF DISEASE TRANSMISSION
(CONTD…)
Three types of Reservoirs:
1. Human reservoir.
2. Animal reservoir.
3. Reservoir in non-living.
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32. DYNAMICS OF DISEASE TRANSMISSION
(CONTD…)
Source/Reservoir MAN
1. HUMAN RESERVOIR
According to Primary case TYPE PORTAL OF EXIT DURATION
spectrum of disease: Secondary case Incubatory Urinary Temporary
Clinical cases Suspect case Convalescent Intestinal Chronic
Sub-clinical cases Healthy Respiratory
Latent infection Others
*Carriers are the most dangerous reservoir for Infections.*
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CASES CARRIERS

33. DYNAMICS OF DISEASE TRANSMISSION
(CONTD…)
1. 2. ANIMAL RESERVOIR
2. Source/Reservoir ANIMAL
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ANIMAL RESERVOIR DISEASE TRANSMISSION
Cattle Bovine TB, Salmonellosis, Tetanus, Q-fever,
Taenia Saginata
Horse Tetanus
Dog Rabies, Hydatid disease
Monkey Yellow fever, Dengue fever
Rodent Plaque, Endemic Typhus
Birds Ornithosis, Histoplasmosis

34. DYNAMICS OF DISEASE TRANSMISSION
(CONTD…)
1. 3. RESERVOIR IN NON-LIVING THINGS
Soil and Inanimate matter act as Reservoirs
E.g.,: Tetanus
Anthrax
Mycetoma
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35. MODES OF
TRANSMISSION

36. 32

37. MODES OF TRANSMISSION
A. DIRECT TRANSMISSION
1. Direct contact
2. Droplet Infection
3. Contact with Soil
4. Inoculation into Skin or Mucosa
5. Transplacental (Vertical)
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38. MODES OF TRANSMISSION (CONTD…)
B. INDIRECT TRANSMISSION
1. Vehicle-borne
2. Vector-borne
a) Mechanical
b) Biological
3. Air-borne
a) Droplet nuclei
b) Dust
4. Fomite -borne
5. Unclean hands
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39. SUSCEPTIBLE
HOST

40. SUSCEPTIBLE HOST
Any person who is at high risk for infection.
An Infectious agent seeks a susceptible host aiming “Successful
Parasitism.”
4 stages are required for successful parasitism:
(i) Portal of Entry
(ii) Site of election in the body
(iii) Portal of Exit
(iv) Survival in External environment
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41. HOST
DEFENCES

42. HOST DEFENCES
1. ACTIVE IMMUNITY:
Immunity which an individual develops as a result of the
Infection or by specific Immunization.
Natural Acquired
(a) Humoral immunity ------ B-cells
(b) Cellular immunity ------ T-cells
(c) Combination of above
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43. HOST DEFENCES (CONTD…)
2. PASSIVE IMMUNITY:
Individual is given antibodies to a disease rather than producing
them through his or her own immune system.
NATURAL ACQUIRED
Maternal antibodies Antibodies developed
transferred to baby in an infected host or
transplacentally or invitro are given
through breast milk. to index host.
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44. IMMUNIZING
AGENTS

45. IMMUNIZING AGENTS
Preparations administered to produce immunity are called
Immunizing agents.
Immunizing agents:
(a) Vaccines ----------------- Active
(b) Immunoglobulins Passive
(c) Antisera
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46. IMMUNIZING AGENTS
(a) VACCINES
Live vaccines
Inactive or killed vaccine
Subunit vaccines
Combinations
(b) IMMUNOGLOBULINS
Normal human Ig
Specific human Ig
(c) ANTISERA
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47. 40

48. NATIONAL
IMMUNIZATION
SCHEDULE

49. 41
NATIONAL IMMUNIZATION SCHEDULE

50. NATIONAL IMMUNIZATION SCHEDULE
(CONTD…)
42

51. NATIONAL IMMUNIZATION
SCHEDULE (CONTD…)
43

52. REFERENCES
1. Park’s Textbook of Preventive and Social Medicine By K. Park (26th Edition), Banarasidas Bhanot
Publishers, Jabalpur, India.
2. IAPSM’S Textbook of Community Medicine By AM Kadri (2nd Edition), Jaypee Publishers.
3. Infectious Disease Epidemiology By Susanne Straif-bourgeois, Raoult Ratard, and Mirjam Kretzschmar.
4. National-immunization-schedule-for-babies-pregnant-women/
5. Images resource: Google
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53. REFERENCES (CONTD…)
https://slidetodoc.com/factors-in-the-spread-of-disease-spread-of-2/
https://www.dictionary.com/e/epidemic-vs-pandemic/
https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html
https://pediaa.com/what-is-the-difference-between-epidemic-and-endemic/
https://www.slideserve.com/arnold/epidemiology-powerpoint-ppt-presentation
https://twitter.com/wellcometrust/status/1423664416743170054
https://www.physio-pedia.com/Endemics,_Epidemics_and_Pandemics
https://www.cdc.gov/onehealth/images/zoonotic-diseases-spread-between-animals-and-people.jpg
https://hivinfo.nih.gov/understanding-hiv/fact-sheets/
https://studylib.net/doc/5745555/iatrogenic-disease
https://communitymedicine4asses.files.wordpress.com/2018/12/National-Immunization-Schedule-
2018-Infants.png?w=682&h=990
https://courses.lumenlearning.com/microbiology/chapter/modes-of-disease-transmission/
https://brooksidepress.org/intramuscular/lessons/lesson-3-immunizations/3-02-immunizing-agents/
https://www.slideshare.net/Drsasi116/immunising-agents-121027427
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54. CREDITS: This presentation template was created by Slidesgo,
including icons by Flaticon, and infographics & images by Freepik
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