Advanced Knowledge of Exotic Animal Diseases and Response Measures

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Exotic Disease Response

• Advanced Knowledge of Exotic Animal Diseases and
  Response Measures

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Training Agenda

• During this session we will cover
• Disease information
• Statistical sampling theory
• Statistical sampling practical
• Response measures
• Relevant legislation.

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Objectives

• By the end of this module you will be able to
• Prepare an information sheet on an exotic disease
• Explain principles of sampling protocols and
  interpretation of laboratory results
• Explain how to collect, store, package and
  document samples
• Explain the Biosecurity response for different
  diseases
• Explain your duties and responsibilities under
  relevant legislation.

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Knowledge Checks

• Are not designed to Pass or Fail you!
• Make sure you have understood what you have
  learned before moving on to the next module.
• You can refer to your reference material
  (processes and procedures) if you need to.
• If you havent achieved 100 accuracy, Ill
  provide some help before we move on to the next
  topic.

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1 Disease information

• Objective
• By the end of this topic you will be able to
• Prepare an information sheet on an exotic
  disease.

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2 Statistical Sampling Theory

• Objective
• By the end of this topic you will be able to
• Explain sampling protocols
• Explain interpretation of laboratory results.

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Process Hierarchies for EDR

• Organism Management
• Manage restricted places
• Security
• De population
• Disposal
• Valuation
• Treatment

• Surveillance
• Investigations
• Tracing
• Field visits
• Provide GIS

• Movement Control
• Assess movement applications
• Monitor movements
• Treatment of vehicles

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What we will cover on statistical sampling theory

• Test types
• Interpreting test results
• Sample size
• Selection of sample

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Prevalence
Apparent prevalence The true prevalence of disease in a population. Can be calculated from AP and test variables.
Expected prevalence The prevalence of a disease as determined by the test.
True prevalence The prevalence of the disease you would expect for the group sampled.
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Sensitivity and Specificity
Sensitivity Measures the ability of the test to correctly identify infected animals (SE)
Specificity Measures the ability of a test to correctly identify disease free animals (SP)
Predictive Value (PV) ve and ve Probability that an animal testing ve (or ve) is actually diseased (or not) Depends on SP, SE and prevalence

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Herd Sensitivity and Specificity
Herd Sensitivity Probability that a test classifies a truly diseased herd ve Function of AP and number of tests
Herd Specificity Probability that a test classifies a truly disease-free herd ve Function of SP and number of tests

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Example 1

Fig 1 True prevalence. 0.
Fig 2 Apparent prevalence. SE90, SP 90.
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Example 2

Fig 1 True prevalence. 20.

Fig 2 Apparent prevalence. SE90, SP 90.
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Example 2
Disease -ve
Disease ve
18 8
2 72
TEST ve SE 90
TEST -ve SP 90.
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Test threshold
Disease -ve
Disease ve
TEST ve SE 90
18 8
2 72
TEST -ve SP 90
20 16
0 64
TEST ve SE 98
TEST -ve SP 80
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Manipulating the threshold
Overlap can move cut-off to change SE and SP
Test -ve
Test ve
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Example interpretation 1

• 1000 pigs, 60 sampled
• SE 95, SP 60
• No clinical signs
• Prevalence 5, ve PV 11
• Prevalence 10, ve PV 21
• Prevalence 50, ve PV 70

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Example interpretation 2

• 1000 sheep, 60 sampled
• SE 95, SP 85
• No clinical signs
• Prevalence 5, ve PV 25
• Prevalence 10, ve PV 41
• Prevalence 50, ve PV 86

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Variables affecting sample size
Expected prevalence If prevalence is lower, sample size is bigger.
Group size If the group sampled is small the proportion sampled is bigger 100 for a very small group.
Confidence () The pre-determined likelihood that a test result is true, ie 95 confident that the animal/herd/region is -ve
Test SE Sample size may be increased to allow for imperfect test Sensitivity
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Expected prevalence
The disease Incubation period, how contagious, species affected etc
Susceptibility Susceptibility varies between species and within a species, different sub groups may be more susceptible
Management practices Housing, movement, opportunity for spread, etc
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Example - Waiheke
Number in group Number of animals to be sampled
1-40 41-50 51-60 61-80 81-120 121-180 181-500 501-1000 All of group 40 45 50 55 60 65 70
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Group Exercise 4 Sample Sizes
In each pair, below, which group might require a
bigger proportion to be sampled and why? Assume
FMD and probability 95
1. 1000 dairy cows 1000 hill country beef cows
2. 500 housed sows 500 sheep
3. 200 sows 2000 sows
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Sample groups
Cows and calves
Cattle
Youngstock
Wethers on run-off
Sheep
Ewes and lambs
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Sampling techniques
Non-random Selecting sample on a basis other than random. For example, all animals with clinical signs, first 50 animals, closest animals to the yards.
Random Randomly sampling properties and/or animals within a group. Every animal has a known, non-zero probability of inclusion in the sample (Dohoo).
Census Sampling all properties and/or all animals.
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Random sampling

• Herd of 500 cows
• Sample required 70
• 500/70 randomly select 1st cow, then every 7th
  cow through the race or dairy

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3 Statistical Sampling Practical

• Objective
• By the end of this topic you will be able to
• Explain how to select a random sample of animals
• Explain how to collect and store samples
• Demonstrate how to pack and document samples.

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What we will cover on statistical sampling
practical

• Sample groups
• Taking samples
• Packing samples
• Documentation
• Field disinfection.

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General rules for taking samples
Bacterial Take these first to reduce chance of contamination. Aseptic techniques. New instruments for each sample. Immediately into media (if used).
PCR Collect second (after bacto) Aseptic techniques. Immediately into media (if used)
Viral Place immediately in transport medium ensure correct medium Chill to around 4 degrees within half an hour
Histology Keep size to 0.5 cm max width Separate pottle for each sample Place in 10 buffered formalin
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4 Response Measures

• Objective
• By the end of this topic you will be able to
• Explain the biosecurity response measures for
  different diseases.

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Response measures depend on

• Herd immunity
• Infectivity
• Cycle interruption
• Portal of entry
• Route of transmission
• Portal of exit
• Reservoir
• Ecology of the agent.

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MAF response measures
GENERIC Response measures
DISEASE SPECIFIC
RESPONSE SPECIFIC Objectives plans
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Overall structures
National Co-ordination
Response Centre
FORT
FORT
FORT
Restricted Place
Restricted Place
Restricted Place
Restricted Place
Restricted Place
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Response phases
Initial Report
Post Response
Investigation
Stand- down
Response
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Phase 1 Initial Report

• Farmer or vet rings MAF 0800 emergency line with
  report of suspicious disease
• Details are taken and decision made on whether to
  investigate (Duty ED Investigator).

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Phase 2 Investigation

• Objectives and plan prepared for the
  investigation (Duty ED Investigator)
• Investigation carried out on farm (Investigating
  Vet)
• Investigation in lab (RC Investigators)
• Notify NCC re results (Duty ED Investigator).

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Phase 3 Response
NCC RC FORT

• Declare response (Director Biosecurity)
• Prepare response objectives
• Co-ordinate response
• Prepares a response plan,
• Activates and instructs FORTs,
• Provides testing, advice, and management
  information services
• Organism Management
• Surveillance
• Movement Control and Treatment

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Phase 4 Stand-down

• NCC declares a stand-down when the disease is
  eliminated or controlled.

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Phase 5 Post Response

• Surveillance continues for a set time after
  stand-down.
• Proof of freedom surveys
• Ongoing surveillance established

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Example Response Objectives

• Maintain essential industries milk collection
• Determine spread within 2 weeks
• Eradicate disease within 6 weeks.

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5 Relevant Legislation

• Objective
• By the end of this topic you will be able to
• Explain your duties and responsibilities under
  the
• HSNO Act
• Animal Welfare Act
• Resource Management Act.

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HSNO Act, 1996

• Packaging, labelling and transport of biological
  samples
• Use of hazardous substances sprays,
  disinfectants, poisons, etc.

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Animal Welfare Act, 1999

• Handling
• Taking samples
• Treatment
• Humane killing.

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Resource Management Act, 1991

• Covers anything that may impact on the
  environment
• Digging holes
• Burning
• Discharge of milk, etc.