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Epidemiology of Equine diseases Flashcards

1
Q

What is frequency?

A

Describes how common an illness (or other health event) is with reference to the size of the population (the population at risk) and a measure of time

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2
Q

What is distribution?

A

Distribution covers time (when), place (where) and person (who)

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3
Q

What is determinants?

A

Covers causes/association, risk factors, modes of transmission (why and how)

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4
Q

What is health?

A

A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity

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5
Q

What is disease?

A

The absence of health

A physiological or psychological dysfunction. Illness is a subjective stat of the person who feels aware of not being well

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6
Q

Why is epidemiology important in an equine context, regarding the UK equine industry?

A

1 million horses in the UK

Owned by 375,000 households

2.4 million people ride

18,000 active equestrian businesses

Employing 250,000 people directly or indirectly

Gross output of £3.4 billion

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7
Q

What are the equine industry priorities?

A

Sustainable horse industry, increase economic value, enhance the welfare of the horse, ensure adequate effective disease surveillance and control

Encouragement and furthering of best practice in all aspects of health, care, husbandry and disease control

Disease control, prevention and treatment should be maintained, whilst acting appropriately, swiftly and effectively as credible new information or new threats emerge.

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8
Q

What is equine influenza caused by?

A

The orthomyxovirus equine influenza A type 2 H3N8 subtype

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9
Q

What is equine influenza?

A

One of the most common infectious diseases of the respiratory tract of horses

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10
Q

What is the incubation period of equine influenza?

A

Short incubation (48hrs)

After this, horses shed large quantities of virus in nasal secretions for 6-7 days

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11
Q

What are the clinical signs and outcomes of equine influenza?

A

Respiratory and may also include fever, oedema and enlarged lymph nodes

Rarely, due to secondary complications, death can occur in very young or old horses

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12
Q

How contagious is equine influenza?

A

Highly contagious and spreads rapidly over large distances (100m) in aerosolised droplets dispersed by coughing or through fomite transmission

The virus can survive for up to 72 hours in the environment

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13
Q

What is prevalence?

A

Measures existing cases of disease and is expressed as a proportion

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14
Q

What is incidence?

A

Measures new cases of disease and is expressed either as a proportion (incidence risk) or in person-time units (incidence rate)

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15
Q

What are some determinants (risk factors) for disease?

A

Biological

Behavioural

Sociocultural

Economic

Ecological

e.g. exposure, independent variable, predictor, explanatory variable

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16
Q

What are some factors that may be determinants for a horse catching equine influenza?

A

Premises with low levels of vaccine coverage

Premisses with limited biosecurity measures, particularly around horse movements

Horseracing (lots of horses together) etc

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17
Q

Why do some horses become infected but others dont?

A

Particularities of the horse, the virus or the environment/horseracing industry that might have contributed to the 2019 equine influenza outbreaks

Epidemiology is about determining how factors interact to cause disease in some but not others

Is an exposure significantly associated with the outcome on average?
Causation is then inferred based on this relationship/association (and other factors)

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18
Q

What is the epidemiological triad?

A

Traditional model of infectious disease causation

Disease occurs as a result of the interaction between hosts, agents, and environments and factors relating to them

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19
Q

Construct an epidemiological triad for equine influenza:

A

Host: Horse
Factors:
- Age (young/old)
- Vaccination status
- Breeding
- Travel history

Agent: Equine influenza virus
Factors:
- Infectivity
- Transmissibility
- Dose

Environment: Livery yard
Factors:
- Humidity
- Housing (e.g. ventilation)
- Biosecurity
- Number of horses

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20
Q

What is a causal web diagram?

A

Provides a way of conceptualising how multiple factors combine to cause disease

The epidemiological triad is a simple version of this, but in reality disease is often an interplay of many direct and indirect causes

21
Q

What questions do epidemiologists use to design and conduct studies? What do these questions relate to?

A

How many cases of disease are in a population?
FREQUENCY

Where do these cases occur?
DISTRIBUTION

Which groups are at an increased risk of exposure to the disease?
DETERMINANTS

How can we halt the progression of a disease in a population?
APPLICATION

22
Q

When should we use descriptive studies?

A

When the research question describes phenomena in a population

23
Q

When should we use analytical studies?

A

When the research question measures associations between risk factors and outcomes

24
Q

What are some examples of descriptive studies?

A

Case Report

Case Series

Surveys

25
What are some examples of analytic studies?
Observational: Cross-sectional Cohort Case-control Experimental: Randomised clinical trials (RCT)
26
What are descriptive studies designed to do?
Describe the nature and distribution of outcomes Provide information about the occurrence of disease Generate hypotheses
27
What are descriptive studies not suitable for?
Investigating associations Making comparisons between groups
28
What is a case report study?
Describes rare condition/unusual case
29
What is a case series study?
Describes a series of cases with a particular outcome
30
What is a survey?
Collect information from individuals in a population, which is then used to describe certain phenomenon within the population
31
What are analytic studies designed to do?
Make comparisons between subgroups of study subjects based on exposure or outcome status Identify statistical associations between exposures (risk factors, treatments) and outcomes Test hypotheses
32
What is an observational analytical study?
Researcher has no control over the allocation of the subjects to the groups being compared Exposed subjects already exist (i.e. they would have been exposed regardless of the study)
33
What is an experimental analytical study?
Researcher controls (through randomisation) the allocation of subjects to the groups being compared Researcher intervenes
34
What is the main difference between observational study designs?
You can distinguish between observational study designs based on how participants were selected
35
How are participants selected in a cross sectional study?
Without regard to exposure or disease status
36
How are participants selected in a cohort study?
Based on exposure status
37
How are participants selected for a case-control study?
Based on disease status
38
What is the process of a cross-sectional study?
Sample a group of individuals without regard to their exposure or disease status e.g. enrol all horses from a livery yard Individuals are examined at the same time to determine exposure and disease status 1. Start with defined population 2. Gather data on exposure and disease status at a single point in time 3. Classify into four groups: - Exposed and diseased - Exposed and not diseased - Not exposed and diseased - Not exposed and not diseased
39
What are the advantages of cross-sectional studies?
Can study exposures and outcomes Relatively fast and inexpensive Good for permanent exposures (e.g. blood type, breed etc)
40
What are the disadvantages of cross-sectional studies?
Not good for rare exposures or outcomes Temporal issues (did exposure or disease come first?) And remember: Collects prevalence not incidence
41
What is prevalence?
A proportion of animals in a defined population that have the outcome under study at a defined instant (point) in time Quantifies existing (prevalent) cases
42
What is incidence?
Quantifies occurrence of new (incident) cases Expressed either as risk or rate
43
What is the process of cohort studies?
1. Individuals are selected and grouped into cohorts based on their exposure status 2. Individuals are followed through time to determine if they develop the disease 3. Must ALL BE DISEASE FREE at the start of the study - Can be prospective or retrospective - Only observational study to establish a temporal sequence Exposed --> Disease develops --> Disease does not develop Not Exposed --> Disease develops --> Disease does not develop
44
What are the advantages of cohort studies?
Good for rare exposures Can establish temporal relationships between exposure/disease
45
What are the disadvantages of cohort studies?
Not good for rare outcomes Long follow-up time Expensive, laborious and time consuming And remember: can collect both prevalence (at end of study period) and incidence (over study period)
46
What is the process of case-control studies?
1. Select/enrol participants based on their disease status - 'cases' or 'controls' 2. Retrospectively investigate whether participants were exposed to the factor of interest in a defined time period 3. Cases and controls then classified as either exposed or non-exposed Select participants based on: Diseased 'cases': - Were exposed - Were not exposed Not diseased 'controls': - Were exposed - Were not exposed
47
What are the advantages of case-control studies?
Good for rare incomes Good for outbreak investigations Often fast and inexpensive
48
What are the disadvantages of case-control studies?
Not good for rare exposures Temporal issues (did exposure really come before the disease) Most subject to bias (e.g. recall bias) And remember: Cannot measure disease frequency i.e. prevalence and incidence

Epidemiology (4 decks)

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