1
Q
Epi + Demios + Logos
o A branch of epizootiology dealing with diseases (health status) in a population
o The study of all factors that determine the frequency and distribution of a disease in a populatio
A
Epidemiology
2
Q
Father of Epidemiology
A
Hippocrates, 400BC
2
Q
The first person known to have examined the relationship between the occurrence of disease and environment influeneces
A
Hippocrates
3
Q
he coined the tern epidemic in his essay entitled “ON AIR, WATER, & PLACES)
A
Hippocrates
4
Q
Introduced the concept of Biostatistics
o Estimation of population
o Construction of life table
A
John Grant (1662):
5
Q
“Counting of natural phenomenon maybe instructive”
o Stated that “Natural and Political observations is related on bills of mortality”
A
John Grant (1662)
6
Q
Introduced the concept of Biostatistics
o Estimation of population
o Construction of life table
A
John Grant (1662):
7
Q
Mosquito transmission of yellow hemorrhagic fever
A
Finlay (1881) and Reed et al. (1900)
7
Q
Cholera outbreak investigation
A
John Snow (1849):
8
Q
Medical statistics
A
William Farr (1839):
9
Q
Cowpox vaccine trials
A
Cowpox vaccine trials
10
Q
Scientists who utilized experiments on man for diseases investigation:
o Lind (1747):
A
Fresh fruit treatment for scurvy
11
Q
Cured rice and beri-beri
A
Fletcher (1905):
12
Q
Diet deficiency and pellagra
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Goldberg (1915)
13
Q
Vaccine trials vs. tropical diseases on American soldi
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WW2:
14
Q
Uses of Veterinary Epidemiology
A
Investigative or diagnostics
o Understanding the disease causation
o Explain the disease patterns
o Describe the natural history of the disease
Implementation of direct actions against the disease
Administrative purposes
15
Q
Diagnostic Disciplines in Epidemiology
A
- Clinical diagnosis: Reductionist approach
- Pathological diagnosis
- Epidemiological diagnosis: Holistic approach
16
Q
pproach in veterinary clinical diagnosis is a focused, detailed method of understanding
disease by dissecting it into its simplest parts, making it a valuable tool in pinpointing specific, treatable
conditions within individual animal
A
Clinical diagnosis: Reductionist approach
17
Q
approach in veterinary pathological diagnosis is a methodical, detailed examination of
tissue and cellular changes, allowing for the precise identification of disease processes. This approach is
crucial for determining the specific nature of pathological conditions, guiding treatment, and contributing
to a deeper understanding of disease mechanisms in animals.
A
Pathological diagnosis: Reductionist approach
18
Q
approach in veterinary epidemiological diagnosis provides a comprehensive understanding
of disease dynamics at the population level. It considers the complex interactions between hosts, agents,
and the environment, focusing on the broader context of disease occurrence.
A
Epidemiological diagnosis: Holistic approach
18
Q
This approach is essential
for developing effective strategies for disease prevention, control, and eradication, ultimately protecting
the health of animal populations and, by extension, public health.
A
Epidemiological diagnosis: Holistic approach
19
Q
Related Fields to Veterinary Epidemiology
A
Clinical Medicine
Pathology
Biostatistics
20
Q
Direct Actions in Epidemiology
A
Studies the nature and extent of the disease problem present in the population
Studies the overall behavior of a particular disease in different populations
Planning and evaluation of efforts to control or prevent the disease
Research on new methods or approaches
21
Q
Three Epidemiological Strategies
Descriptive
o Answers the following:
A
What is the event of the phenomenon?
Which are the animals involved?
When did it take place?
Where did it take place?
Why and How did it occur?
22
Tools Used in Descriptive Strategy:
Scientific Methods
Description of the problem
Generation of hypothesis
Testing of hypothesis
Formulation of a solution
Conclusion
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Hypothesis
Explanation or a proposition that can be tested by facts that are known or can be obtained.
24
Methods in Formulating Hypothesis:
Method of difference:
In two different sets of circumstances, one factor can be absent on the
other
25
In Epidemiology, it includes the following:
Population
Determinant
Response or expected effect
Dose-Response Relationship
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One factor is common to all sites of circumstances
Method of agreement:
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Frequency or strength of a factor varies with the frequency of
the disease
Method of concomitant variation:
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Distribution of the disease may be sufficiently similar to the other support to
a common cause
Method of analogy:
29
Descriptive Study Designs:
Case Report:
Case Series:
Ecologic Studies
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Documents unusual medical occurrences, a careful and detailed report on the profile
of a single patient, represents the first clues in the identification of new diseases or adverse
effects of exposure
Case Report:
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Collection of individual case reports which may occur within a short period of time
Case Series:
32
Experimental Epidemiologic Strategy:
Designing special propositions and experiments to test the epidemiological hypothesis
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Statistical inferences about the disease in a population from the available samples of the proposition
Analytical Epidemiologic Strategy:
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Analytical Epidemiologic Strategy:
Complicated mathematical methods (sampling techniques and other techniques) are needed to:
-Determine the strength of epidemiological association
-Determine the importance of associations
-Determine the statistical significance of the associations
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Disease in a Population
Analytic Study Designs:
Analytic Observational Studies:
Experimental Studies:
36
Analytic Observational Studies:
Case Control studies
Cohort studies
Cross-sectional studies
37
Sampling without regard to the exposure or disease status
Cross-sectional:
37
Experimental Studies:
Quasi-experiment
Experimental studies
Cross-sectional:
Cohort (Longitudinal) Studies:
Case Control (Longitudinal) Studies:
38
Sampling is on the basis of exposure status
Cohort (Longitudinal) Studies:
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Sampling is on the basis of disease status
Case Control (Longitudinal) Studies:
40
is essential for assessing the spread of diseases, designing
control measures, and implementing effective management practices.
"The Population"
41
refers to the entire group of animals that are of interest in a particular study or surveillance
activity. This population can include livestock, companion animals, wildlife, or even vectors like insects that
may carry diseases.
"The Population"
42
is defined by specific characteristics, such as species, geographical location,
or the type of farming system. Accurate characterization of the population is critical for understanding disease
dynamics, assessing risks, and planning interventions.
"The Population"
43
unit are the basic entities of interest when studying disease prevalence, conducting risk
assessments, or implementing disease control measures. For instance, in a dairy farm, the herd is the
primary population unit; in a wildlife study, a species within a specific reserve might be the focus. The
population unit defines the scope and scale of veterinary interventions.
Population Units
43
Types of Population
1. Open Population:
2. Closed Population:
44
Is one where there is regular movement of individuals into and out of the population. This can include
livestock populations where animals are frequently bought, sold, or moved between farms, or wildlife
populations where animals migrate or disperse across different areas.
Open Population:
45
The constant influx and outflux of
animals can significantly impact the spread and control of diseases, as new individuals may introduce
pathogens or be exposed to existing ones. Epidemiological models for open populations must account for
this dynamic movement to accurately predict disease transmission and outcomes.
Open Population:
46
Regular movement of individuals within the population.
Open Population
46
Estimation of Population Size
1. Censusing
2.Population Sampling Method
3. Relative Population Indices
47
Is one with little to no movement of individuals into or out of the population. This situation might be
found in isolated wildlife populations or in certain types of livestock operations where biosecurity
measures prevent the introduction of new animals.
Closed Population:
48
the disease dynamics are
generally more stable and predictable since there is no external influence from new individuals.
However, once a disease is introduced, it can persist within the population if not effectively managed, as
there are no new susceptible individuals entering the population. Closed populations are often easier to
study epidemiologically, but they also require vigilant disease monitoring and control to prevent
outbreaks.
a closed population, t
49
Little or no migration at all.
Closed Population
50
involves directly counting every animal in a population, such as in a livestock herd or wildlife
population, within a defined area. This method is used to determine the exact number of animals that could be at
risk of disease or could serve as reservoirs for infections.
censusing
50
provides precise data but can be labor-
intensive and is often impractical for large or mobile animal populations.
censusing
51
Population at Risk (PAR)
For example,
young calves might be a population unit at
risk for respiratory diseases, while older cattle may be more prone to metabolic disorders. Understanding which
population units are at risk helps in targeting prevention and control measures effectively.
51
is a state where a host organism is invaded by another organism (the symbiont), such as bacteria,
viruses, or fungi. The symbiont establishes itself within the host, which may or may not lead to disease. In
veterinary medicine, infections can be asymptomatic or cause illness, depending on various factors like the
virulence of the pathogen and the host's immune response.
Infection
51
involves estimating the size of an animal population by studying a sample group.
This approach is often used
when it's impractical to count every animal.
2. Population Sampling Method
51
For example, researchers might sample a subset of farms to estimate
the prevalence of a disease in a larger area.
Techniques like random sampling or systematic sampling are used to
obtain data, which is then extrapolated to estimate the population size and the potential impact of diseases.
51
Population at Risk (PAR)
Infection
Infestation
Commensalism
Parasitism
Transmissible or Communicable Disease.
51
to a specific group of animals that are susceptible to a particular disease due to factors like age,
species, environment, or preexisting health conditions.
Population at Risk (PAR)
52
are used to estimate trends in animal populations or the prevalence of diseases.
These indices rely on indirect measures, such as the frequency of animal sightings, tracks, or droppings, to infer
population size or density.
3. Relative Population Indices
52
Although these indices do not provide exact population numbers, they are valuable
for monitoring changes in animal populations over time, particularly in wildlife, where direct counting may be
difficult.
3. Relative Population Indices
53
specifically refers to the presence of ectoparasites, such as fleas, ticks, or mites, on the skin or hair of
an animal. These parasites live on the external surface of the host and can cause irritation, discomfort, or
secondary infections. Infestation is distinct from infection as it involves external parasites rather than internal
pathogens.
Infestation
54
the symbiont benefits from residing on or within the host without causing any apparent harm.
For example, certain bacteria that live in the intestines of animals may aid in digestion without causing disease.
This type of relationship is characterized by a lack of noticeable symptoms or health issues in the host.
Commensalism
55
occurs when the symbiont benefits from its relationship with the host at the host's expense. This
includes many infectious diseases where the pathogen causes harm or illness to the host. Examples include
diseases like parasitic worms or protozoal infections that actively damage the host’s tissues or organs.
Parasitism
56
is one that can spread from an infected host to a susceptible host. This
spread can occur through various means, such as direct contact, respiratory droplets, or contaminated surfaces.
Effective control of communicable diseases often involves measures to interrupt transmission routes.
Transmissible or Communicable Disease.
57
those that require close or intimate contact for transmission between hosts. This often
means that the disease spreads easily through direct physical contact or through close proximity in environments
like pens or stables. Contagious diseases can spread rapidly in confined or densely populated settings.
Contagious diseases
58
Symbiotic state wherein the body of an organism (host) is invaded by another
(symbiont).
Infection
59
Limited to ectoparasitism (skin/hairs).
Infestation
60
The symbiont benefits from invading the host but does no harm
(subclinical or inapparent infection).
Commensalism
61
The symbiont benefits from invading the host and harms the host (infectious
disease).
Parasitism
62
When the disease passes from one infected
host to a susceptible host.
Transmissible or Communicable Disease:
63
Connotes “intimate” contact with an infected host.
Contagious
64
Disease Determinants
The Epidemiologic Triad
-Host Determinants
-Specific Agent Determinants
-Environmental Determinants
-Time Determinants
(McMahon)
-Combinations of the
Above (McMahon)
65
Disease is the result of forces within a dynamic system called an
"EPIDEMIOLOGIC TRIAD"
66
Host Determinants
Intrinsic Host
Determinants:
Extrinsic Host
Determinants:
67
Species,
breed, hereditary features,
sex, resistance (natural or
acquired), age,
physiological state.
Intrinsic Host
Determinants:
67
Animal
use, level of husbandry.
Extrinsic Host
Determinants:
68
Resistance:
Natural Resistance:
Acquired Resistance
68
Inborn/innate ability to resist infection through normal anatomical structure and
physiological functioning of the body. Non-specific.
Natural Resistance
69
Host’s Resistance
Resistance:
Sum total of the defensive mechanisms that the body possesses, implying a varying level of protection.
70
Intact skin, intact mucosa, reflexes, phagocytosis.
Natural Line of Defense: (natural resistance)
71
Acquired Resistance: Not inborn/innate.
Types:
Active Acquired: Natural, Artificial.
Passive Acquired: Natural, Artificial
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Infectivity, pathogenicity, virulence, latency, patency, incubation/prepatent period,
period of communicability.
Properties of Living Agent:
73
Agents’ Determinants
Properties of Living Agent:
Portals of Entry/Exit of Agent to the Susceptible Hosts:
74
Respiratory tract, GIT, membranes, percutaneous,
genito-urinary tract, transplacental, mechanical.
Portals of Entry/Exit of Agent to the Susceptible Hosts:
75
Environmental Determinants
Physical: Topography, climate, season, weather.
Biological: Plants and animals, man.
Socio-economic: Population density and distribution, socio-political structure, economic development.
76
Time Determinants
1. Diurnal and Short-term Changes.
2. Seasonal Changes.
3. Cyclical Changes.
4. Secular Changes.
77
Variations in disease incidence or health parameters that occur within a
single day or over a few days. For example, the prevalence of certain infections in animals may fluctuate based on daily
feeding schedules or environmental conditions.
1. Diurnal and Short-term Changes
78
Changes in disease patterns or health status that occur with the seasons. For instance,
respiratory infections in livestock may increase during colder months or wet seasons due to environmental stressors.
2. Seasonal Changes.
79
Recurrent changes in disease patterns or health conditions that follow a regular cycle, such as
annual or multi-year intervals. Examples include certain parasitic infestations that peak at regular intervals based on life
cycles of parasites or vector populations.
3. Cyclical Changes.
80
Long-term trends or changes in disease patterns over extended periods, often years or decades.
These changes can be influenced by factors like environmental shifts, changes in management practices, or genetic
evolution of pathogens
4. Secular Changes.
81
Interaction between determinants significantly causing the occurrence of --
disease
82
When the disease occurs widely and invariably
Sporadic
82
Describing Disease Occurrence
Patterns of Disease Occurrence
Sporadic:
Endemic
Epidemic
Pandemic
83
Predictable regularity of disease in a population. Examples: Malaria, arthritis, high blood pressure.
Endemic
84
Classifications of Endemicity:
: Holoendemic, Hyperendemic, Mesoendemic, Hypoendemic.
85
When the disease is present in excess of its expected frequency. Examples: Measles, influenza,
plague.
Epidemic
86
Important to help identify the regular patterns of disease events and select the most appropriate study approach
to a disease phenomenon.
Temporal Distribution of Disease
86
expressing the increase and decrease of the number of new disease cases, and the rate (speed)
of disease changes.
Epidemic Curves
Incidence curves
86
Worldwide occurrence of disease. Example: 1918 Spanish flu.
Pandemic
87
Ordinate
New cases
88
Abscissa
Time
89
Temporal Trends of Disease Occurrence
Short Term Trend:
Cyclical Trend:
Long Term or Secular Trend:
90
Atypical epidemics indicating a disturbance between the host and the agent.
Short Term Trend:
91
Associated with regular, periodic fluctuations in the level of disease occurrence.
Cyclical Trend
92
Changes in disease frequency occurring gradually over long periods of time.
Long Term or Secular Trend
93
Sporadic outbreaks.
Random
93
Detecting Temporal Trends
Time Series Analysis:
A record of events that occur over a period of time, plotted as points on a graph with
time along the horizontal axis.
94
Spatial Distribution of Disease
Trends:
Contagious Spatial Pattern
Random
Regular
94
An infectious agent propagates in the population.
Contagious Spatial Pattern:
95
A cartographic method to express the spatial distribution of events.
Isodemic Mapping
95
Regular spacing of disease.
Regular
96
Types of Isodemic Mapping:
Spot maps, grid maps, transparent maps, isopleth maps, computer-
generated maps.
97
An interaction between the places of onset and the times of disease occurrence.
Disease Mapping and Spatial Epidemiology using GIS
Time – Space Clustering
5- Epedimiology
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