Epidemiology is the study and analysis of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare. Epidemiologists help with study design, collection, and statistical analysis of data, amend interpretation and dissemination of results (including peer review and occasional systematic review). Epidemiology has helped develop methodology used in clinical research, public health studies, and, to a lesser extent, basic research in the biological sciences

1. INTRODUCTION OF
EPIDEMIOLOGY
Pradhuman Yadav
B.v.Sc & a.h

2. ONE WORLD ONE
HEALTH
 One World: Earth
 One Health: Humans, Animals, Environment
 Emerging Infectious Disease (EID)
 Avian Influenza (H5N1),
 SARS (Severe Acute Respiratory Syndrome)
 Nipah virus
 Influenza A (H1N1)

3. EMERGING INFECTIOUS DISEASES
 infectious diseases with an increasing in
patient report over the past 20 years
 infectious diseases with an increasing
possibility in the near future
 AIDS, Avian Influenza, and drug resistant
tuberculosis
 Antimicrobial resistant organisms

4. RE-EMERGING INFECTIOUS DISEASES
 infectious diseases that used to create
outbreak in the past and subsided for a nu
mber of years but are occurred again
 tuberculosis, hemorrhage fever and malaria

5. Emerging and re-emerging
Infectious Diseases

6. Global of emerging and re-emerging infectious diseases

7. FACTORS OF EID
 Humans (Africa, Asia and Latin America)
 Wildlife (Forest encroachment)
 Climate change
 Pathogens
 Spread of pathogen (air or insect)
 Virus (mutation)

9. EPIDEMIOLOGY
 Epi = on, upon
 Demos = people
 Logos = knowledge

10. HISTORICAL OF
EPIDEMIOLOGY
 Hippocrates (400 BC)
 John Graunt (1662)
 John Snow (1854)
 Out break of cholera occurred in a small area
of central London (Golden Square)

11. WHAT IS EPIDEMIOLOGY?
 The study of the distribution and
determinants of health-related states or
events in specified populations and the a
pplication of this study to the control of h
ealth problems (CDC)

12. WHAT IS EPIDEMIOLOGY?
 focused on the health and disease status
of a population
 the study of how disease is distributed in
populations and the factors that influence
or determine this distribution

13. Epidemiology
is a scientific disciplinediscipline
that involves the studystudy of
the frequencyfrequency and distributiondistribution
of healthhealth and diseasedisease
in populationspopulationsin order to find risk factorsrisk factors
for preventionprevention and controlcontrol

14. Discipline: the general approach is to creating order and
structure from incomplete knowledge
Study: combines learning about epidemiology theory with
on the job field application
Frequency: means that we count characteristics in a
population of people or animals
Distribution: describes the patterns of disease in a
population, in a particular place during a period of time

15. Health: refers to measures of optimum productivity
due to lack of disease (meat, eggs or milk)
Disease: refers generally to an imbalance in the health
status of individuals or populations that result in
decreased productivity, illness or death
Population: refers to the group of individual animals or
people that are considered or affected

16. Prevent: means not providing the opportunity for a
disease to occur
Control: method to reduce the extent of disease in a
population or area
Risk factors: risk is the probability that a factor the
population is exposed to be associated with the
occurrence of disease

17. OBJECTIVE OF EPIDEMIOLOGY
 To identity the etiology (cause) of disease
and the relevant risk factors
 To determine the extent of disease found in
the community
 To study the natural history and prognosis of
disease

18. OBJECTIVE OF EPIDEMIOLOGY
 To evaluate both existing and newly
developed preventive and therapeutic
measure and modes of health care
delivery
 To provide the foundation for developing
public policy relating to environmental
problems

19. Use of Epidemiology
• Describe the distribution of disease
• Describe the natural history of disease
• Identify factors that increase/decrease risk
• Predict trends
• Consider mechanisms of transmissions
• Test efficacy & evaluate interventions
• Identify health needs

20. Epidemiology Clinical medicine
Population People (Case)
Prevention and control Treatment
Epidemiologist Case
Healthy in population Healthy in people
Epidemiology VS Clinical medicine

21. FIELD EPIDEMIOLOGY
 Field Epidemiology is the front linefront line
 There is health emergency or an immediate
need to understand the health status of a
population
 Emerging Infectious Disease (EID): no
information, very limited

22. FIELD EPIDEMIOLOGY
 Attempts to gather and organize data to
bring order and meaning to it
 Can be applied to disease outbreaks,
situation assessments and policy evaluation.
 Relies on a systematic approach to gather
and organize data in a way that will support
a better understanding of a disease situation

23. GOAL OF
VETERINARY FIELD EPIDEMIOLOGY
 Prevention and control disease agents
 Health of animals, humans and environment
 Concepts and methods of epidemiology
 Practical and information

24. EPIDEMIOLOGY APPROACH
 Try and understand what factors may be
increasing or reducing the risk of disease
 Promoting and protecting the health of
animal and human populations

25. ENDEMIC
 the constant occurrence of a disease that
commonly presentscommonly presents in a particular place with
stability in the level of infection
 Sporadic: An irregular occurrence of a disease
that commonly presents in a particular place

26. Endemic pattern
Sporadic pattern

27. EPIDEMIC
 the occurrence of a disease that the level of
infection exceeds that normal expectancy
in a specific region, spreads rapidly and
usually lasts for a limited period of time
 Pandemic: widespread epidemic that affects a
large part of population in many countries
 Epizootic: epidemic that involves animal host
population

28. Epidemic pattern

29. EPIDEMIC PATTERNS

30. DISEASE OUTBREAK
 survey of disease data
 count of cases
 describe
 person / animal
 place
 time

31. Epidemiology triad: explain why diseases occur in a population

32. Environment
Host Agent
Environment
Host
Agent
Environment
Host
Agent

33. Environment
Host Agent
Environment
Host Agent

34. AGENTS
 Biological
 Viruses Bacteria Parasites or prions
 Chemical
 Toxins
 Man-made (Dioxins and melamine)
 Inorganic/organic: zearalenone
 Physical
 Foreign bodies
 Trauma
 Radiation

35. AGENT FACTORS
 Dose
 Environmental hardiness
 Virulence (microbial)
 Infectivity (microbial)
 Toxicity (poisons)

36. HOST
 Natural host:
 agent has adapted itself and co-exists in
balance in the host
 Atypical host:
 agent is not normally encountered

37. HOST
 Demography
 Age, Sex, Species, Breed
 Production type / level, Density
 Biology
 Genetics, behavior
 Management
 Intensive (housing) / extensive (free roaming)
 Nutrition
 Hygiene
 Husbandry
 Vaccination / medication

38. HOST
 Marketing
 Profitability related to prices (economics)
 Distance from market
 Herd immunity
 Innate (genetic capability)
 Acquired through vaccination or deliberate
exposure
 Proportion of total population that is resistant to a
disease agent
 Susceptibility
 Lack of resistance to the disease agent

39. HOST FACTORS
 Innate resistance (e.g. gastric barrier,
mucocilliary transport mechanism)
 Previous exposure
 Passive immune status (neonates)
 Vaccination status and response
 Age
 Gender

40. HOST FACTORS
 Behavior (e.g. mutual grooming, dominance, pica)
 Production status (e.g., lactating vs. non-lactating)
 Reproductive status (e.g., pregnant vs. non-
pregnant, sterile vs. intact)
 Genetics

41. ENVIRONMENT
1) Natural environment
 Geography
 Climate
 Season
 pH
 Ammonia concentration
 Water activity
 Ultraviolet light
 Organic matter

42. 2) Human aspects
 Animal management systems
 Marketing systems and economics
 Government policies

43. ENVIRONMENTAL
FACTORS
 Animal stocking density
 Animal movement between groups
 Housing (e.g. ventilation, sanitation)
 Environmental conditions (e.g. temperature,
humidity, wind velocity, precipitation)
 Nutrition (protein, energy and macromineral and
micromineral adequacy)

44. EXAMPLE
"Bovine mastitis is a disease of man with signs in the cow."
"Bad management will overwhelm the best immunology."
• Increased animal density may lead to increased
microbial load in the environment
•a roof may prevent exposure of microbe to killing UV
• low ventilation
• increase humidity
• increases environmental survival of the organism
• increases exposure dose and infects more
animals.

45. NATURAL HISTORY OF
DISEASE
Normal
Risk factors
Disease
Death
recover
disabled

46. NATURAL HISTORY OF DISEASE
 Stage of susceptibility
 Stage of preclinical disease
 Stage of clinical disease
 Stage of disability

47. ICEBERG PRINCIPLE OF DISEASE

48. ICEBERG (PHENOMENON) PRINCIPLE

49. ICEBERG
PHENOMENON
deathdeath
disabilitydisability
ClinicalClinical
ClinicalClinical
Pre-clinicalPre-clinical
SusceptibilitySusceptibility
HealthyHealthy

50. •Clinical
•Sub-clinical
Outcome
Host
susceptibility
Exposure
Agent source
Steps in the Disease Process

51. CONCEPT OF
CAUSATION
 The basis for most epidemiological
investigations
 To identify causal relationships and potential
risk factors
 A framework for identifying causes of
infectious disease

52. KOCH’S POSTULATES
 The agent has to be present in every case of
the disease.
 The agent has to be isolated and grown in
pure culture.
 The agent has to cause disease when
inoculated into a susceptible animal and th
e agent must then be able to be recovered f
rom that animal and identified.

53. CAUSATION OF DISEASE
 The agent
 Is present when the disease exists
 Is absent when the disease does not exist
 The agent can be isolated in pure culture and
results in disease when it is given to exposed a
nimals
 Exposure
 Occurs before the disease occurs

54. CAUSATION OF DISEASE
 Consistency
 The disease is reproducible in different populations at
different times
 Strength of statistical association
 The results are not due to chance
 Dose-response
 Increase in exposure leads to increase in disease

55. SOURCES OF INFECTIOUS DISEASE
 Environment
 Live Animals / Dead animals
 Feed and Water
 Animal products
 Animal by-products
 Reservoir (wild animals, insects)
 Fomites (clothing, equipment, vehicles)
 Vectors (insects)

56. EXPOSURE
• Initial introduction into the population
• Transmission within the population
• Direct transmission
• Horizontal
• Vertical
• Indirect transmission
• Marketing systems
• Exposure dose of disease agent
• Route of exposure
• Animal density

58. HOST SUSCEPTIBILITY
 Species, breed, strain
 Age
 Sex
 Genetics
 Animal management and husbandry

59. INFECTIOUS DISEASE
 Three terms are used to describe an
infectious disease according to the various
outcomes that many occur after exposure to
the causative agent and their population
based definitions are given below
 Infectivity
 Pathogenicity
 Virulence

60. INFECTIVITY
 the percentage (or proportion) of individuals
exposed to a particular agent who become
infected
No of infected following exposure
Total of population at exposure
Infectivity =

61. PATHOGENICITY
 the percentage of infected individuals who
develop clinical disease due to the
particular agent
No of clinically affected following exposure
Total of infected at exposure
Pathogenicity =

62. VIRULENCE
 the percentage of individuals with clinical
disease who become serious ill or die
No of severe (fatal) cases following exposure
Total of clinically infected cases at exposure
Virulence =

63. Mode of Transmission
• Direct Transmission
– Direct contact
– Droplet spread
• Indirect
– Air borne
– Vehicle borne (food water)
– Vector borne (arthropods: ticks, mosquitoes)

64. • Influenza: droplet spread, vehicle borne
• Salmonella: vehicle borne, direct contact
• TB: air borne
• Cutaneous Anthrax: direct contact
• Pneunonic Plague: air borne

65. TYPE OF EPIDEMIOLOGY (STUDY
DESIGN)
 Descriptive epidemiology
 survey: time, place, person
 Case report, case series
 Analytical epidemiology (risk factors)
 Cross-sectional
 Cohort
 Case-control
 Experimental epidemiology
 Randomized control trial
 Clinical trial
 Community trial

66. Epidemiology study
Distribution Risk factors
Analytic studyDescriptive study

67. DESCRIPTIVE
EPIDEMIOLOGY
Epidemiology
Distribution
Risk factors
Time
Place
Person
Analytic study
Descriptive study
Etiology

68. DESCRIPTIVE EPIDEMIOLOGY
 What (How much): occurred
 Who: animals or humans
 When: time
 Where: place

69. DESCRIPTIVE EPIDEMIOLOGY
 Detection of individual case
 Detection of outbreaks
 Measuring the impact of disease
 Understand the nature of a disease
 Understand the way that disease spreads
and is distributed

70. DESCRIPTIVE EPIDEMIOLOGY
 Generate hypotheses and ideas for further
research
 Evaluation of prevention and control
measures
 Support planning activities for animal health
program

71. BASIC MEASURES AND TOOLS OF
DESCRIPTIVE EPIDEMIOLOGY
 Data collection
 classification / organization
 summarizing
 presentation

72. INCIDENCE
 the number of NEW cases that develop
over a certain time period.

73. INCIDENCE RATE
No. of new cases of a disease occurring in the population
during a specified period of time
No. of persons who are at risk of developing the disease
during that period of time
x100

74. PREVALENCE
 the number of existing cases including old
and new cases that have developed at som
e point during a time period.

75. No. of cases of a disease present in the population
at a specified time
No. of persons in the population at that specified time
Prevalence rate
x100

76. INCIDENCE AND PREVALENCE

78. EXAMPLE
Question Type of measure
Do you currently have asthma? Point prevalence
Have you had asthma during the last 2 years? Period prevalence
Have you ever had asthma? Cumulative incidence

79. No of clinically ill
Population
Morbidity rate =
No of infected
Population
Infection rate =

80. No of deaths
Population
Mortality rate =
No of deaths
No of clinically ill
Case fatality rate =

81. ANALYTICAL EPIDEMIOLOGY
 How: adjust policy and response
 Why: prevent and control

82. CROSS-SECTIONAL
 A random sample of individuals from a
population is taken at a point in time
 Surveys to collect data

83. CROSS-SECTIONAL
 Advantages:
 quick to conduct and cost is moderate
compared with other study designs.
 Disadvantages:
 cannot provide information on the incidence of
disease in a population only an estimate of
prevalence
 Difficult to investigate cause and effect
relationships

84. COHORT
 Comparing disease incidence over time
between groups
 Prospective cohort
 Non-disease case
 Expose and non-expose
 Retrospective cohort
 Disease case
 Evaluated for evidence of exposure to the agent

85. Cohort

86. COHORT
 Advantages:
 monitored over time for disease occurrence
 estimates of the absolute incidence of disease in
exposed and non-exposed
 Disadvantages:
 long follow-up period
 case of rare diseases large groups are necessary
 Losses to follow-up
 expensive

87. CASE-CONTROL
 Comparing the frequency of past exposure
between cases who develop the disease (or
other outcome of interest) and controls
chosen to reflect the frequency of exposure
in the underlying population at risk

89. CASE-
CONTROL
 Advantages:
 an efficient method for studying rare diseases
 subjects have experienced the outcome of
interest at the start of the study
 quick to run and cheaper than other study
 Disadvantages:
 Can not provide information on the disease
incidence in a population
 Reliant on the quality of past records or
recollection of study participants
 Difficult to ensure an unbiased selection of the
control group