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Introduction of Epidemiology

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Title: Introduction of Epidemiology


1
Introduction of Epidemiology
  • SUNPETCH ANGKITITRAKUL, Ph.D.
  • ??????? ?????????????

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 number 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)

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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 application of this study to
    the control of health 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 discipline
that involves the study of
the frequency
and distribution
of health and disease
in populations
in order to find risk factors
for prevention and control
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
Risk factors risk is the probability that a
factor the population is exposed to be associated
with the occurrence of disease
Prevent means not providing the opportunity for
a disease to occur
Control method to reduce the extent of disease
in a population or area
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 VS Clinical medicine
Epidemiology Clinical medicine
Population People (Case)
Prevention and control Treatment
Epidemiologist Case
Healthy in population Healthy in people
21
Field Epidemiology
  • Field Epidemiology is the front 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 ofVeterinary 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 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
Relax
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35
Agents
  • Biological
  • Viruses Bacteria Parasites or prions
  • Chemical
  • Toxins
  • Man-made (Dioxins and melamine)
  • Inorganic/organic zearalenone
  • Physical
  • Foreign bodies
  • Trauma
  • Radiation

36
Agent Factors
  • Dose
  • Environmental hardiness
  • Virulence (microbial)
  • Infectivity (microbial)
  • Toxicity (poisons)

37
Host
  • Natural host
  • agent has adapted itself and co-exists in balance
    in the host
  • Atypical host
  • agent is not normally encountered

38
Host
  • Demography
  • Age, Sex, Species, Breed
  • Production type / level, Density
  • Biology
  • Genetics, behavior
  • Management
  • Intensive (housing) / extensive (free roaming)
  • Nutrition
  • Hygiene
  • Husbandry
  • Vaccination / medication

39
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

40
Host Factors
  • Innate resistance (e.g. gastric barrier,
    mucocilliary transport mechanism)
  • Previous exposure
  • Passive immune status (neonates)
  • Vaccination status and response
  • Age
  • Gender

41
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

42
Environment
  • Natural environment
  • Geography
  • Climate
  • Season
  • pH
  • Ammonia concentration
  • Water activity
  • Ultraviolet light
  • Organic matter

43
  • 2) Human aspects
  • Animal management systems
  • Marketing systems and economics
  • Government policies

44
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)

45
Example
  • 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.
  • "Bovine mastitis is a disease of man with signs
    in the cow."
  • "Bad management will overwhelm the best
    immunology."

46
Break 15 mins
47
Natural history of disease
48
Natural history of disease
  • Stage of susceptibility
  • Stage of preclinical disease
  • Stage of clinical disease
  • Stage of disability

49
Iceberg principle of disease
50
Iceberg (phenomenon) Principle
51
Iceberg phenomenon
52
Steps in the Disease Process
53
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

54
Kochs 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 the agent must then
    be able to be recovered from that animal and
    identified.

55
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
    animals
  • Exposure
  • Occurs before the disease occurs

56
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

57
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)

58
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

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Host susceptibility
  • Species, breed, strain
  • Age
  • Sex
  • Genetics
  • Animal management and husbandry

61
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

62
Infectivity
  • the percentage (or proportion) of individuals
    exposed to a particular agent who become infected

Infectivity
63
Pathogenicity
  • the percentage of infected individuals who
    develop clinical disease due to the particular
    agent

Pathogenicity
64
Virulence
  • the percentage of individuals with clinical
    disease who become serious ill or die

Virulence
65
Mode of Transmission
  • Direct Transmission
  • Direct contact
  • Droplet spread
  • Indirect
  • Air borne
  • Vehicle borne (food water)
  • Vector borne (arthropods ticks, mosquitoes)

66
  • Influenza droplet spread, vehicle borne
  • Salmonella vehicle borne, direct contact
  • TB air borne
  • Cutaneous Anthrax direct contact
  • Pneunonic Plague air borne

67
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

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Descriptive epidemiology
Time
Distribution
Place
Descriptive study
Person
Epidemiology
Risk factors
Analytic study
Etiology
70
Descriptive epidemiology
  • What (How much) occurred
  • Who animals or humans
  • When time
  • Where place

71
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

72
Descriptive epidemiology
  • Generate hypotheses and ideas for further
    research
  • Evaluation of prevention and control measures
  • Support planning activities for animal health
    program

73
Basic Measures and Tools of Descriptive
Epidemiology
  • Data collection
  • classification / organization
  • summarizing
  • presentation

74
Incidence
  • the number of NEW cases that develop over a
    certain time period.

75
Incidence rate
x100
76
Prevalence
  • the number of existing cases including old and
    new cases that have developed at some point
    during a time period.

77
Prevalence rate
x100
78
Incidence and Prevalence
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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
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Analytical epidemiology
  • How adjust policy and response
  • Why prevent and control

85
Cross-sectional
  • A random sample of individuals from a population
    is taken at a point in time
  • Surveys to collect data

86
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

87
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

88
Cohort
89
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

90
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

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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

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confuse
95
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