1 Exotic Disease Response Advanced Knowledge of Exotic Animal Diseases and Response Measures.

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Exotic Disease ResponseAdvanced Knowledge of Exotic Animal Diseases and Response Measures

Advanced Knowledge of Exotic Animal Disease and Response Measures

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

Training Agenda


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ObjectivesBy 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 haven’t achieved 100% accuracy, I’ll 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

1. Test types2. Interpreting test results3. Sample size4. 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 +veFunction of AP and number of tests

Herd Specificity Probability that a test classifies a truly disease-free herd –veFunction of SP and number of tests


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Example 1

Fig 1: True prevalence. 0%.

Fig 2: Apparent prevalence. SE=90%, SP= 90%.


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Example 2

Fig 1: True prevalence. 20%.

Fig 2: Apparent prevalence. SE=90%, SP= 90%.


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Example 2 …

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2 72TEST: -ve

SP = 90%.

Disease -veDisease +ve

TEST: +ve

SE = 90%


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Test threshold18 8

2 72TEST: -ve

SP = 90%

Disease -veDisease +ve

TEST: +ve

SE = 90%

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0 64TEST: -ve

SP = 80%

TEST: +ve

SE = 98%


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Manipulating the threshold

Overlap –can move cut-off to change SE and

SPTest -ve

Test +ve


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1000 pigs, 60 sampled

SE 95%, SP 60%

No clinical signs

Prevalence 5%, +ve PV = 11%



Example interpretation 1


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1000 sheep, 60 sampled

SE 95%, SP 85%

No clinical signs




Example interpretation 2


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Variables affecting sample sizeExpected 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

1-4041-5051-6061-8081-120121-180181-500501-1000

All of group40455055606570


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Group Exercise 4 – Sample Sizes

1. 1000 dairy cows 1000 hill country beef cows

2. 500 housed sows 500 sheep

3. 200 sows 2000 sows

In each pair, below, which group might require a bigger proportion to be sampled and why?

Assume: FMD and probability 95%


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Sample groups

Cows and calves

Sheep

Cattle

Youngstock

Wethers on run-off

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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Herd of 500 cowsSample required – 70500/70 = randomly select 1st cow, then every 7th cow through

the race or dairy

Random sampling


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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

1. Sample groups2. Taking samples3. Packing samples4. Documentation5. 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 mediumChill to around 4 degrees within half an hour

Histology Keep size to 0.5 cm max widthSeparate pottle for each samplePlace 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

Restricted

Place

Restricted

Place

Restricted

Place

Restricted

Place

Restricted

Place

FORT FORT FORT

Response Centre

National Co-ordination


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Response phases

Initial

ReportInvestigation Response Stand-

down

Post

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• 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

NCC

RC

FORT


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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

1. Packaging, labelling and transport of biological samples

2. Use of hazardous substances – sprays, disinfectants, poisons, etc.


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Animal Welfare Act, 1999

1. Handling

2. Taking samples

3. Treatment

4. Humane killing.


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Resource Management Act, 1991

Covers anything that may impact on the environment;

1. Digging holes

2. Burning

3. Discharge of milk, etc.

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1 Exotic Disease Response Advanced Knowledge of Exotic Animal Diseases and Response Measures.

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