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Disease Epidemiology > Animal Health Surveillance > Flashcards

Animal Health Surveillance Flashcards

1
Q

What is animal health surveillance?

A
  • Identifies important disease events in animal populations
  • Allows farmers, vets, and government disease control agencies to develop timely and appropriate responses to either eradicate, control, or mitigate the adverse effects of diseases
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2
Q

WHO definition of surveillance

A

The ongoing systematic collection, collation, analysis and interpretation of data and the dissemination of information to those who need to know in order for action to be taken

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3
Q

Components of disease surveillance systems

A
  1. Early detection
  2. Early response
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4
Q

Early detection

A
  • Uses a defined disease monitoring system
  • Involves a defined level or threshold of disease at which an intervention should take place
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5
Q

Early response

A

A defined set of interventions that will be undertaken if and when the threshold is reached. The interventions will vary based on disease and its impact on public health and economics

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6
Q

General purposes of disease surveillance

A
  • Demonstrating freedom from disease
  • Early detection of disease
  • Measuring the level of disease
  • Finding cases of disease
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7
Q

Key steps when disease is not currently or usually present

A
  • Early detection
  • Demonstrate freedom
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8
Q

Key steps when diseases are present

A
  • Case finding
  • Measure level of disease
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9
Q

What kinds of diseases are not currently or normally present?

A
  • Exotic diseases (eg. African swine fever)
  • Emerging diseases (eg.Lyme disease)
  • New diseases
  • Epidemic diseases (ex.Anthrax)
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10
Q

What is an emerging disease?

A

Recently identifiable diseases that are changing in their importance due to increased host range, pathogenicity or spread

Eg. Lyme Disease

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11
Q

What is an epidemic disease?

A

Diseases which may be present but appear sporadically in the form of an outbreak

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12
Q

Why is it important to demonstrate freedom of a disease?

A
  1. Trade access- ability to export animals or animal products
  2. Trade barriers- allows country that has demonstrated freedom to prevent imports
  3. Stopping control or eradication measures that have been in place
  4. Public health measures could be lifted if freedom demonstrated from a zoonotic disease
  5. Political reasons
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13
Q

Why is it important to have early detection?

A
  • Early response increases effectiveness of eradication or control programs
  • Also prevents the spread to other countries if caught early enough
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14
Q

Endemic Diseases

A

Diseases that are always present in the population

Can determine if they are at baseline (normal within specific population), increasing or decreasing

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15
Q

Spatial distribution of disease

A

Understanding spatial risk factors

  • Establishing disease free zones

Ex. Disease in eastern Canada, but not in western Canada

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16
Q

Temporal distribution of disease

A
  • Monitoring control programs over time by looking at trends including early detection of changes in endemic disease
  • Identify risk factors for disease and production practices that influence disease status
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17
Q

Finding cases of disease

A
  • Identify individual cases or individual outbreaks
  • Usually part of a disease control program
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18
Q

Disease control program examples

A
  • Bovine spongiform encephalitis (BSE)
  • Tuberculosis lesions at slaughter
  • Tuberculosis testing in countries where it is endemic (Eg. UK)
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19
Q

Criteria to meet surveillance objectives

A
  1. Timeliness
    - How quickly surveillance system can produce information
    - How often surveillance period is
  2. Population coverage
    - What proportion of population is covered by system
  3. Representativeness of surveillance sample
    -Represent all of population
    -Bias towards more severe cases
20
Q

Criteria for early detection surveillance system

A
  • Be continuous
  • Have comprehensive coverage of the population
  • Be sensitive enough to detect low levels of prevalence (cases)
21
Q

Criteria for a surveillance system that demonstrates freedom

A
  • Does not need to be continuous but needs to be intermittent or ad hoc
  • Can use risk-based sampling to increase efficiency
  • Uses a higher design prevalence than early detection
22
Q

Criteria for surveillance system for measuring disease

A
  • Can be ad hoc (when needed) or periodic
  • Should be based on representative sampling to avoid bias
  • Needs a large enough sample to give adequate precision
23
Q

Criteria for surveillance system for case finding

A
  • Use comprehensive coverage of the population. Risk based approaches can focus on high risk parts of population
  • Ongoing coverage
  • Have good individual herd or animal sensitivity
24
Q

Factors affecting surveillance systems

A
  • Timing of data collection (continuous, intermittent, ad hoc)
  • Source of data (animal owners, vets, labs, abbatoir, retail)
  • Sampling method (risk based vs. representative vs. sentinel)
  • Level of detail/case definition (syndromic surveillance)
25
Q

Two main types of surveillance systems

A
  1. Passive surveillance
  2. Active surveillance
26
Q

Passive surveillance

A

Relies on spontaneous reports of disease suspicions reported by many different individuals (vets, animal producers, etc.)
- Includes using existing data sources that are collected for other reasons
- Observer initiated data collection (diagnostic laboratory data, Promed electronic reporting system)

27
Q

When is passive surveillance used?

A
  • Less expensive method because information being collected anyways for other reasons
  • Often used to identify new and emerging diseases (Ex. cryptococcus gattii in BC- fungal infection popping up in province)
28
Q

Downside to passive surveillance systems

A
  • Takes a lot of work to collect data, analyze and make it useful
  • Continuous but not representative (not many animals come in for post-mortem; more sick individuals more likely to be reported)
  • Can’t always extrapolate to the general population
  • Often stigmatised diseases, mild diseases, diseases with unfavorable cost-benefit ratios, low prevalence are not represented well in passive surveillance
29
Q

Active surveillance

A

Purposeful collection of information often targeting a specific disease

  • “Investigator-initiated data collection”
  • More expensive surveillance
  • More accurate estimate of disease frequency

Examples: surveys, sentinel surveillance systems, mass screening programs

30
Q

Larry Brilliant and Smallpox

A

Played a huge role in eradication of smallpox by going house to house, finding cases and vaccinating individuals in the area

31
Q

Risk based or targeted surveillance

A
  • Surveillance is targeted at populations that are more likely to have the disease or are in an area where the disease is more likely to be introduced
  • Used for freedom of disease or early detection purposes
  • Optimizes use of surveillance resources
32
Q

Examples of risk based or targeted surveillance

A

Surveillance for BSE in Canada
- Disease is rare so random sampling would be very inefficient
- Focus on high risk animals (4D: diseased, down, dying, or dead)

33
Q

Sentinel surveillance

A

Look at sentinel units (herds, vet clinics, flocks) that are chosen to intensively monitor over a period of time
- Repeated visits to sentinel sites
- Antibody status often used to determine exposure
- Measures freedom of disease
- Early warning system
- Geographic distribution (when conducted at margins of disease-free and endemic zones)

Sometimes considered a risk-based or targeted surveillance

Ex. Cages of chickens outside in Western Canada and kept sampling them

34
Q

Abattoir surveillance (or other aggregation points)

A

Constant supply of surveillance data

  • Inexpensive as they are be inspected anyway
  • Can cover large number of animals
  • Single aggregation points for animals from generally wide range
  • Can be both active or passive surveillance
  • Potential bias because healthy well grown animals
  • Lack of associated data such as origin of animal
35
Q

Syndromic surveillance

A

Groups clinical diseases into syndromes rather than specific diagnoses (Eg. Neurological disease)

Uses clinical reports to find specific syndromes. Need large amounts of data. Should be fast, simple and cheap to get

  • Indicator based surveillance
  • Potentially useful for early detection of disease outbreaks and detection of unknown diseases
  • Can result in false alarms
36
Q

Random sampling

A

Every member in population has an equal probability of being sampled in the surveillance system

37
Q

Sampling type considerations

A
  • What is the main objective
  • Do we need a representative sample or a risk-based sample?
  • What is the sampling unit? (herd, individual, kennel)
  • How accessible is population? (wildlife vs domestic animals)
38
Q

Simple Random sampling

A

Selecting a fixed percentage of the population using a formal random process

Use sampling frame (ex. list of individuals in population)

39
Q

Systematic random sampling

A

Sampling units are selected from the sampling frame at regular intervals

Ex. every 5th farm

40
Q

Stratified random sampling

A
  • Sampling units selected from strata (breed, gender, herd size)
  • Can be selected by simple random or systematic random sampling
41
Q

Cluster sampling

A

Randomly select groups (herds, litters, etc.) and then sample all individuals of the group
- Groups selected through simple or systematic random sampling
- Infectious disease clusters within herds
- May lead to an underestimate of the variability of the disease

42
Q

Multistage sampling

A

Use random sampling methods at 2 levels (herd level= primary sampling unit, and the individuals in the herd= secondary sampling unit)

43
Q

Sample size

A
  • Rare disease= need to sample more individuals
  • More individuals= more accurate
  • Samples sizes need to be 95%/99% confident that disease is present at or below specified prevalence
44
Q

Challenges in building good surveillance systems

A
  • Buy in and participation
  • Data integration and analysis
  • Confidentiality and data sharing
  • Maintaining vigilance
  • Convincing practitioners of the value of the info they are collecting
  • Diagnostic tests for identifying disease (sensitivity/specificity)

** Hard to build surveillance systems that are interconnected between surveillance centers

45
Q

Classic surveillance activities

A
  1. Mandatory reporting
    - Include both federally reportable diseases (ex. avian influenza, equine infectious anemia) and provincially reportable diseases
  2. Active surveillance for specific diseases
    - Formally designed surveillance plans
    - Usually to do with export or public health concerns
    - Ex. BSE
  3. Passive surveillance at labs & abattoirs, markets, dead stock (rejections, test results, cause of death, lesions)
    - Have tons of data, that can be analyzed into epidemiological data
    - Differences across different data centers makes it very hard to collate data between them
  4. Export testing and certification
    - Important in national surveillance
    - Criteria based on demands from importing countries
46
Q

Western Canadian Animal Health Network (WeCAHN)

A

Fledgling organization modeled after RAIZO and OAHN
- Includes 4 western provinces
- Start in 2020

Disease Epidemiology (9 decks)

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