EPI 2

Question 1

What are the 2 main things diagnostic tests must classify and the measure of these

Answer 1

1. Correctly class diseased animals as diseased
   - Diagnostic Sensitivity
2. Correctly class non-diseased animals as non-diseased
   Diagnostic Specificity i

Question 2

What does high sensitivity and high specificity imply

Answer 2

High Sensitivity implies a low number of false negatives

High Specificity implies a low number of false positives

Question 3

Define sensitivity and specificity

Answer 3

Sensitivity -> number of true positives within the disease animals
Specificity -> the number of true negatives within the non-diseased animals

Question 4

What are the 2 important questions when applying diagnostic tests and what equations answer this

Answer 4

1. An animal has come up test positive to a particular condition, what is the probability of the animal really having the condition?
   - Positive Predictive Value (PPV)
2. An animal has come up test negative, what is the probability that the animal is really free from the condition?
   - Negative Predictive Value (NPV)

Question 5

How to make a diagnosis and therefore how diagnostic tests work and their downfall

Answer 5

• Aim is to correctly identify abnormalities -> Normal Vs Abnormal -> for this wee need to define boundaries around normality - THE TEST
  How to you separate the populations uninfected and infected?
  Almost impossible for most tests always going to have false positives and false negatives

Question 6

Define a test and list some examples

Answer 6

Any procedure that reduces uncertainty about the state of disease

• questions posed during history taking,
• clinical signs (examination and measurements) - CLINICAL EXAMINATION IS A TEST
• lab findings (haematology, serology, biochemistry, histopath),
• post mortem findings
• Gold standard is what we are sure will give us the result

Question 7

What are 3 general types of tests and how to know which on to use and if choose wrong what will this affect

Answer 7

Categorized by what they measure
1) physiological or production parameter
2) agent, antigens or nucleic acid
3) animals immune response to challenge (antibodies)
Depends on the point of disease you are testing, unlikely to see antibodies at the start of disease but will see virus and vice versa
Effects SENSITIVITY - may not pick up the disease

Question 8

What are the two general categories for things measured by diseases and which harder

Answer 8

• Binary outcome (+/-, pregnant versus not pregnant)
• Continuous outcome (heart rate, blood albumin, ab titre)
  • need to set a cut-off to define what is normal versus not

Question 9

What is the perfect diagnostic test, do they exists and how to measure the validity of the test

Answer 9

Perfect -> Would allow us to differentiate between disease positive and disease-negative individuals without error
• Does not exist – the tests that we use are imperfect
• To know how good they are we need to evaluate them against a reference

Question 10

List and describe 7 characteristics that make for a valid diagnostic test

Answer 10

1) fitness for intended purpose -> accurate and precise
2) robustness (reliability) -> unaffected by small changes in test situation
3) repeatable -> within and between runs in one lab
4) reproducible -> between runs in different labs
5) Diagnostic sensitivity -> few false negatives
6) Diagnostic specificity -> few false positives
5 and 6 -> when tested in animal of known infection status in target population
7) thresholds -> cut-off selection

Question 11

When is high sensitivity important

Answer 11

• a high cost from calling a diseased animal negative:
• Screening -> testing all animals -> pick up most as positive then later may do a high specific test to ensure that it is a true positive
• quarantine/testing new stock entering a herd)
• testing for something rare (<1% prevalence)

Question 12

What is need high sensitivity and specificity what tests would you do in what order

Answer 12

When screening for a disease

1) Capture all animals that is positive -> don’t want to miss any -> High sensitivity
2) Confirmation -> follow-up work -> ensure all are true positive - High specificity

Question 13

When is high specificty important

Answer 13

• a high cost from calling a non-diseased animal positive:
  ○ confirmatory testing
  ○ Depopulating (killing) based on test results
  ○ trade impacts when you get false positive results
• ruling-in (confirmation):

Question 14

What are 2 main ways of improving accuracy, the types within and what does this increase and therefore decrease

Answer 14

1. Use several tests instead of a single test:
   - Parallel testing(OR) –the animal is considered infected if it is positive to ANY test.
   ○ ↑ SENSITIVITY, ↓ false negatives -> decrease specific
   - Serial testing (AND) –the animal must be positive to ALL test to be considered infected.
   ○ ↑ SPECIFICITY, ↓ false positives -> decrease sensitivity
2. Use a different cut-off point for the context
   - But always a trade-off
   ○ Improving sensitivity will reduce specificity and vice versa.

Question 15

Predicative valves what d they vary with and the 3 things needed to calculate

Answer 15

• PREDICTIVE VALUES VARY WITH PROBABILITY (PREVALENCE) OF THE CONDITION -not a constant trait of the test!
  3 estimates:
• Sensitivity - set for the test
• Specificity - set for the test
• Pre-test probability - variable
  ○ the probability of the animal having the condition PRIOR to testing (an estimate/guestimate of prevalence can be used)

Question 16

How does positive and negative predictive values change with change in prevalence

Answer 16

• PPV goes down with low prevalence

- NPV goes down with high prevalence

Question 17

what is post-test predicative value and how to get with negative and positive predictive value

Answer 17

Post-test predictive value is the value of the cow being infected given the predictive value
= positive predictive value and the remaining percent with the negative predictive value

Question 18

What are surveys used for and what get when have a perfect test

Answer 18

• Surveys may be conducted to estimate the prevalence of a condition in a population
• What can be directly estimated is apparent prevalence, the % animals that test positive, not the real (true) prevalence
• True prevalence is the estimate you’d get with a perfect test

Question 19

Define an outbreak

Answer 19

series of disease events clustered in space and time

Question 20

List the 5 steps in problem solving

Answer 20

1) Evaluate solution
2) define and analyses problem
3) gather information
4) identify solutions
5) choose and implement solution

Question 21

What are the 3 aims of an outbreak investigations and what type of approach is needed

Answer 21

• To identify the problem/cause -> problem solving, structured process
• To control it
• To prevent it
  Systematic approach
• Applied (field) epidemiology involves collecting information for action!
  Aim to identify modifiable causal factors AND prevent further cases

Question 22

List 3 contexts for investigations and what approaches are needed

Answer 22

1) Single agent clear cut outbreak (anthrax in Northern Victoria) -> diagnose, treat and prevent
2) Multi-agent/confused picture -> systematic investigation required (the 7 steps)
3) Emergency animal disease – 1 case is an outbreak -> contain and investigate (again the 7 steps)

Question 23

With a single agent clear cut outbreak is occurring what are the 4 things success depends on

Answer 23

• true diagnosis being considered
• only one disease being present
• the results of examinations being definitive for the disease
• traditionally assumed risk factors apply

Question 24

With a multi-agent outbreak what are 4 main challenges

Answer 24

•New, emerging, exotic or unfamiliar diseases may not be considered on the differential diagnosis list
○ Fear, unsure of how to proceed, higher stakes if zoonotic
•Misinformation, uncertainty, fear
•Time pressure
•Multifactorial disease complexes (e.g. bovine respiratory disease)

Question 25

Stevenson’s First Law of Veterinary Science list 2

Answer 25

* Multiple clinical signs in an individual animal tend to have a single aetiology (cause/agent). * A single syndrome in a population (e.g. infertility, decreased milk production) tends to have multiple aetiologies.

Question 26

With emergence animals diseases what are the 5 objectives

Answer 26

* determine whether containment and eradication can be achieved * identify other infected and suspected premises (IPs and DCPs) * intervene immediately to achieve the most appropriate outcome * identify system failures that lead to the outbreak * prevent re-occurrence

Question 27

What are the 3 main things involved with outbreak investigations

Answer 27

1. clinical & environmental & management investigations 2. laboratory investigations 3. epidemiological investigations

Question 28

What are the 7 steps taken in an outbreak investigation

Answer 28

1. Verify the outbreak and the diagnosis 2. Define, identify and count cases 3. Describe outbreak according to individual, place & time 4. Formulate working hypotheses 5. Evaluate and test hypotheses 6. Implement control and preventive measures 7. Communicate findings

Question 29

Step 1 in outbreak investigation: Verify outbreak & diagnosis what are the 4 features

Answer 29

1) Are you really dealing with a problem -> observed cases greater than expected 2) what is the problem -> definition of disease 3) other factors -> severity, public relations, political considerations, risk of spread zoonoses 4) make a diagnosis -> list differentials, history, clinical examinations

Question 30

Step 2: Define, identify & count cases what need to do and what includes

Answer 30

Case definition -> clinical laboratory diagnostic criteria, information about affected region. specification of time during which the outbreak occurred

Question 31

What does a good case definition ensure and allow you to do

Answer 31

- ensures consistency of diagnoses across place and time (specific time period) - allows to calculate appropriate measures of disease frequency -> allows you to rule cases in or out - helps to monitor responses to interventions

Question 32

Step 3 of outbreak investigation: Individual, place and time what is needed for this step and what is involved

Answer 32

ONCE HAVE CASE DEFINITION •Describe outbreak according to the individual: •Describe outbreak according to place: •Describe outbreak according to time:

Question 33

List Risk factors within animal management and environment categories

Answer 33

Animal Age, sex, breed, size, pregnancy Management Feed, water, drug treatment, pen location, stocking rate Environment Weather, climate, wind speed, proximity to wildlife

Question 34

How do you describe the outbreak according to individuals

Answer 34

- compare affected animals with unaffected animals - what are the characteristics of affected and unaffected animals in terms of exposure to potential risk factors, age, production level, stage of production cycle? calculate attack rates

Question 35

How do you describe the outbreak according to place

Answer 35

- where are the affected and unaffected animals located? - because different groups or pens of animals often have different levels of exposures a dose-response relationship exists for many aetiologic agents, this is an important set of clues 1) random 2) clustered - most common 3) regular

Question 36

How do you describe outbreaks according to time

Answer 36

- when in calendar time did the problem actually begin? - be careful of ‘pseudoepidemics’ caused by the onset of producer awareness of a more chronic problem or caused by a change in problem definition (or change of staff) - epidemic curves 1) Propagating epidemic 2) Point source epidemic

Question 37

Step 4 of an outbreak investigation: Develop hypotheses how is this down

Answer 37

- by combining information formed from step 1-3 - prioritise your hypotheses by their likelihood and focus your efforts on those with the highest priority until they are either more fully supported or are refuted

Question 38

Step 5 of an outbreak investigation: Evaluate & test hypotheses how is this done

Answer 38

1) predict what you should find in other animals, such as test results or production effects, and proceed accordingly to test your predictions 2) concentrate on cases in the middle of the epidemic curve (not the beginning or the tail end) 3) recall bias -> ask subjects about what they would do on a ‘typical’ day (as opposed to trying to solicit precise details for the period prior to the onset of illness)

Question 39

Step 6 of an outbreak investigation: Implement control & preventive measures what involved

Answer 39

- hands on, practical advise - short-term, long-term, prevention - monitor progress

Question 40

Step 7 of an outbreak investigation: Communicate findings how done

Answer 40

As professional provide a written report of findings - case report - gives client evidence of your efforts (justifies the bill) - provides a valuable record for future reference

Question 41

Define monitoring and surveillance

Answer 41

Monitoring - Regularly observing the health of a population to observe tends in disease Surveillance - observing the health/ disease status of a population and taking action when disease reaches a specified threshold

Question 42

List 6 reasons to conduct surveillance

Answer 42

1. Observe health trends - 2. Rapid detection -> exotic or new emerging disease important 3. Identify new and emerging disease -> within another species or area 4. International trade obligations -> very important in terms of 5. Plan and identify disease priorities -> which areas you need to focus on, 6. Evaluate interventions -> need to monitor and evaluate

Question 43

List 7 components of a surveillance program

Answer 43

1) objectives 2) case definition 3) target population 4) timing of sampling intervals 5) data management 6) methods for data analysis and triggers for action 7) feedback and dissemination of results

Question 44

Notifiable diseases in Victoria what is the vets legal responsibility and in what time frame with 1) exotic diseases 2) serious 3) less serious

Answer 44

- Your legal responsibility to report on SUSPICION within define timeframes ○ Exotic animal disease and anthrax notify immediately ○ Serious but not exotic disease within 12 hours ○ Less serious notifiable disease - within 7 days to the Chief Veterinary Officer

Question 45

World organisation for animal health list some objectives and the reason for global reporting

Answer 45

- Transparency - Scientific information - International solidarity - Promotion of veterinary science - Sanitary safety - Food safety and animal welfare Global reporting - All about risk management - Countries know what is happening within their trade partners - Can take measures to ensure countries don't get certain diseases -> biosecurity insurance system

Question 46

What are the 3 main types of surveillance programs and types within

Answer 46

- Active vs passive -> data collection - General vs targeted -> disease focus - Structures vs unstructured -> sampling method Types within 1) Risk-based surveillance 2) Sentinel "" 3) Participatory "" 4) Syndromic "" 5) Rumour ""

Question 47

Describe active vs passive surveillance

Answer 47

ACTIVE - main users of info make active efforts to collect the data -> surveys, specific testing programs PASSIVE - main users of info take no action to initiate the collection of data -> secondary data is used -> reporting of clinical cases

Question 48

Describe general vs targeted surveillance

Answer 48

GENERAL - monitors animal population to detect undefined and unexpected -> scanning TARGETED - answers specific question about define diseases or condition

Question 49

Give an example of a targeted surveillance system within Australia

Answer 49

- National TSE Surveillance Program (NTSESP): Mad Cow Disease (BSE) & Scrapie ○ Objective to demonstrate Australia free/early detection ○ Sampling adult cattle or sheep with neurological signs § Testing focused on samples from downer cows ○ Want the brain stem for samples

Question 50

What occurs with sentinel surveillance

Answer 50

- Animals are susceptible to the disease - Place in the area that unsure whether the disease is present in an area - If seroconvert or get disease then disease in present in that area § How many seroconvert give you prevalence - Victorian Arbovirus disease surveillance use sentinel chickens

Question 51

Participatory disease surveillance what type of surveillance and what are the 4 main features

Answer 51

- Forms of active surveillance ○ Community consultation ○ Resource intensive ○ Syndromic case definition -> more relying on symptoms and signs rather than laboratory evaluations ○ More qualitive underlying of context -> disease, impacts, responses at community level

Question 52

Describe Syndromic surveillance and what can achieve

Answer 52

- automated data acquisition and generation of statistical alerts allows one to monitor disease indicators in real-time or near real-time - case definition based on signs & symptoms, not on laboratory confirmation - in theory allows earlier detection of outbreaks/disease than with traditional methods

Question 53

List 5 things that are needed to conduct surveillance

Answer 53

1) Owners recognising and reporting disease in animals (communication. Compensation) 2) Veterinary infrastructure: sampling and recording outcomes 3) Lab infrastructure for diagnose 4) Political will and resourcing 5) Cooperation (national and international)

Question 54

When monitoring disease frequency what is the goal and how achieve

Answer 54

``` accurate information is the goal ○ Accuracy implies freedom from error: § There are only two types 1. Systematic Error (Bias) 2. Random Error (Chance effects) - Monitoring systems should be designed to eliminate as many sources of bias as possible and to contain random error within tolerable bounds ```

Question 55

List 6 attributes of effective surveillance systems

Answer 55

1) Simplicity - if too difficult decrease motivation to report and act 2) Flexibility - to detect emerging (unknown) diseases 3) Sensitivity - a high detection rate 4) Specificity - a low number of false (positive) alarms 5) Representativeness 6) Timeliness – detect and allow for action within a timeframe relative to the infectious cycle of the disease so that further cases can be prevented

Question 56

What does disease control strategies suggest

Answer 56

- Disease control implies doing something to ○ Reduce morbidity due to disease OR ○ Reduce mortality of the disease

Question 57

List and briefly describe 9 disease control strategies

Answer 57

1) movement restriction on people, equipment and animals 2) quarantine - incubation and infectious periods 3) Biosecurity - isolation and testing 4) Outbreak investigation and surveillance 5) vaccination - ring or blanket 6) treatment - reduce shedding 7) vector and reservoir control 8) humane slaughter and disposal 9) do nothing -> wait and see NOT EXOTIC DISEASES

Question 58

What are the 4 things that aradication implies you are doing

Answer 58

○ completely remove the disease from the population ○ prevalence↓ → no transmission ○ prevalence↓ → no major problem, but transmission ○ cause a disease to become extinct in a region or zone within a country (elimination)

Question 59

What are the 7 WHO criteria that suggest eradication is a good option

Answer 59

1) epidemiologic susceptibility 2) effective practical intervention available 3) demonstrated feasibility 4. Consensus on perceived community cost to benefit 5. Synergy with other interventions 6. Need for eradication rather than control 7. Compensation and financial support for short-term losses

Question 60

What are the 3 general things need for effective surveillance and eradication programs

Answer 60

technical - availability of resources, economic and social factors Social -> farmers have reasons not to report, communication to increase awareness, enhance biosecruity is important (needs to be cost effective)