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EVIDENCE BASED MEDICINE - 2 > 12a - Disease Investigation Outbreak I > Flashcards

12a - Disease Investigation Outbreak I Flashcards

1
Q

Why do we investigate outbreaks?

A
  • Service to producers and veterinarians
  • Active disease surveillance tool
  • Direction for research
  • Valuable source of teaching material
  • *infectious disease to toxicities
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2
Q

What is an outbreak?

A
  • A series of events clustered in time AND space ABOVE what we expect by chance alone or history
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3
Q

What is outbreak investigation? (‘medical detection’)

A
  • A systematic procedure to ID causes (risk factors) of disease outbreaks and impaired productivity
  • One of the most interesting and challenging aspects of herd medicine
  • *one of the first steps in a long-term herd production and health management program
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4
Q

What are the 3 objectives of outbreak investigation?

A
  1. Halt the progress of disease
  2. Determine reasons for the outbreak
  3. Recommend procedures to reduce the chance of future outbreaks
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5
Q

What are the procedures for investigating herd outbreaks?

A
  • Define the problem: WHAT
  • Define the groups: WHO, WHEN, WHERE
  • Collect samples
  • Establish a working diagnosis: WHY
  • Take action: written report with recommendations for action
  • FOLLOW-UP
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6
Q

Define the problem: WHAT

A
  • Listen to the story
  • SHOW ME
  • Clinical exams
  • Decided IF there is a problem
  • Necropsies
  • *a problem well-defined is ¾ of the solution
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7
Q

Data gathering: 3 main things

A
  • Initial contact
  • Herd visit
  • Collection of sample
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8
Q

Data gathering: Initial contact

A
  • Don’t diagnose herd problems over the phone
  • Be a good listener
  • Do NOT jump to conclusions
  • Don’t ask leading or loaded questions
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9
Q

What does the herd owner need to prepare for data gathering and a herd visit?

A
  • Collect and review important records
  • Preliminary questionnaire?
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10
Q

What does the veterinarian need to prepare for data gather and a herd visit?

A
  • Working case definition
  • Review risk factors
  • Contact the lab
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11
Q

Data gathering: herd visit

A
  • Talk to everyone
  • Timing is important
  • Document your findings
    o Written notes
    o Camera, video
    o Samples
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12
Q

Data gathering: herd visit ‘steps’

A
  1. Review story in chronological order and look at herd background and management practices
  2. Start defining important ‘groups’
  3. Examine the animals
    a. Need a good case definition
  4. Examine the environment
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13
Q

Herd visit: define important ‘groups’ (EXAM)

A
  • Age groups, temporal cohorts, spatial cohorts
  • For feed lot
    o Farm of origin
    o Truck loads
    o Pens, sick pens
  • *record location of all management groups! (maps, drawings, photos)
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14
Q

Herd visit: examine the animals

A
  • Clinical examination: DETAILED
  • Walk through
  • Distant exam
  • BCS
  • Count and record
  • *work from healthy to sick
  • *use gloves
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15
Q

Herd visit: need a good case definition

A
  • Need one to compare cases to non-cases
  • Comparing clinical cases to sub-clinical cases
  • *if not in right category=can lead to loss of POWER for the investigation
  • *iceberg concept
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16
Q

Herd visit: examine the environment

A
  • Verify herd management info (ex. how often are they actually bedding?)
  • Observe feeding management: mineral or feed ‘always’ out
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17
Q

What varies greatly across herd owners? (and influences if there is a ‘real problem’)

A
  • Management experience
  • ‘threshold of concern’
  • *sometimes there is NO problem (ex. 2 abortions in 150 cows)
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18
Q

What are pseudo-epidemics caused by?

A
  • Onset of producer awareness of a more common problem OR caused by a change in problem definition
  • Ex. change from visual observation of abortion to early pregnancy palpation or ultrasound in a dairy herd
  • *use own data or data from the literature
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19
Q

“The dead pile never lies”

A
  • Necropsy ALL available cadavers
    o Notes and pictures
    o Use new technologies (histopathology OR immunohistochemistry to get confirmation
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20
Q

What are some problems collecting postmortem data?

A
  • Necropsy material examined by more than one prosecutor
  • *diagnosis based on ‘quantitative pathology’ rarely offered
  • *make sure there is COORDINATION
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21
Q

Herd that had an 80% increase in calf mortality: 20 postmortem exams

A
  • Need to put the information together
    o Severe enterocolitis
    o Villus and crypt loss and necrosis
    o Lymphoid depletion
  • *NEED A SYSTEM FOR COLLECTING SAMPLES AND COMBINING THE RESULTS
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22
Q

Tissues you collect: some you may not think of

A
  • Thyroid gland
  • Thymus
  • Salivary gland (Ex. Vit A deficiency=squamous metaplasia)
  • Sciatic nerve
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23
Q

You need to ID important groups and establish herd inventory

A
  • Body condition score
  • Establish pregnancy status
  • Record group affiliation
    o Different management, pastures, feeding?
24
Q

What is the importance of collecting samples?

A
  • Need ADEQUATE NUMBER of animals to recognize PATTERNS ACROSS GROUPS
    o Acute vs. chronic
    o Diseased vs. normal
    o Between locations
    o Young vs. old
25
Q

Lab analysis can help define the problem and ID who is affected

A
  • Often only ONE chance to collect samples
    o Timing is CRITICAL
    o Further access to animals may be impossible
  • *look for things I can find (ex. horse)? Or start hunting (ex. zebra)?
    o Ex. Salmonella is a ‘zebra’ in beef still in Canada
26
Q

Collecting samples

A
  • Right containers and coloured tubes
    o Blue=trace mineral testing
  • Ex. Brisket tagger for a round biopsy
  • *consider limitations associated with sensitivity and specificity of lab tests (know before you take the samples)
27
Q

What are the 7 S’s for sampling?

A
  • Suck: blood
  • Scoop: poop
  • Swab: nose, eyes, etc
  • Slice: necropsies
  • Spoon: feed
  • Siphon: water
  • Specify: ID (have tags with you, need to be able to ID the animal after the fact)
28
Q

Collection of samples: talk to the lab and verify the

A
  • Appropriated specimen
  • Collection procedure
  • Amount
  • Container
  • Storage and transport instructions
29
Q

Avoid ‘fishing expeditions’ when sampling

A
  • *sampling without an objective
    o Seldom useful
    o Expensive
    o Loss of time and credibility
30
Q

Consider sample banking

A
  • Many can do well in freezing or liquid nitrogen
  • Save the $$ to begin before you know if you need to test
31
Q

Establishing or verifying the pathological and etiological diagnosis

A
  • Recognize that in many cases ONLY establishing a definitive pathologic or etiologic diagnosis does NOT solve the producers problem
32
Q

Farm with an abortion problem, colleague wants to test for N. caninum. What do you tell/ask him?

A
  • What do we have to work with (aborted fetuses)?
  • What other species?
  • Other producers in the area?
  • *Objective: trying to just know the reason or prevent something in the future?
33
Q

How can you evaluate risk factors?

A
  • ID important groups and look for patterns of disease
  • Look for patterns and natural experiments
  • Orient by subject (who), place (where, map) and time (when, epidemic curves)
  • *literature review
  • *path models
34
Q

Epidemic curves: ‘type’ of epidemic

A
  • Point source
  • Sporadic
  • Endemic problem
  • Propagated
35
Q

Point source epidemic

A
  • Rapid rise in cases, then decline
  • Ex. toxin
36
Q

Sporadic epidemic

A
  • Few cases scattered or time (no pattern)
37
Q

Endemic problem

A
  • Consistent over time
  • Ex. staph. Aureus mastitis in dairy herds
38
Q

Propagated epidemic

A
  • Continues over time
  • Initial group exposed and then another group exposed or moved in
  • *need to differentiate it from point source epidemic
39
Q

Path models

A
  • Someone else has pulled together main risk factors for a particular problem
  • Ex. neonatal losses due to infectious disease or due to accidents
40
Q

What 2 main factors affect weaning weight? (‘risk factors’)

A
  • Age of the calf (younger=not as heavy)
    o More of a reproductive problem
  • Are they gaining weight like we want? (nutrition, etc.)
  • *how can you differentiate between? (take age out of the equation)
41
Q

Attack rate tables

A
  • Compare percent of sick animals across suspected risk factors
    o Exposed vs. unexposed
  • Which factor(s) are most associated with disease?
42
Q

Examine the herd records?

A
  • Do you have access to computerized records?
  • Evaluate quality of records
  • Have herd owner do as much as practical and possible
  • *often hardest part to get paid for
43
Q

*What is prevalence?

A
  • EXISTING cases divided by population at risk
  • *disease AT some point in time)
44
Q

*What is incidence?

A
  • NEW cases in period/total population at risk
  • *disease DURING a given period of time
  • *equals risk or attack rate
45
Q

**What is the equation for relative risk (RR)

A
  • Attack rate for positive heifers divided by attack rate for negative heifers
  • *account for uncertainty with p-value (p<0.05) and confidence intervals (95% CI)
    o Do not want RR=1 in CI (same as having a p>0.05)
  • **risk factor with the highest RR is a place to start looking for the cause of the problem
  • *when you know/include all
46
Q

**Odds ratio (EXAM)

A
  • When do a case-control study
    o We decided/determined control and cases=cannot use RR
  • *estimate of RR
    o Can be poor sometimes (overestimate)
  • *do when we only have a subset
47
Q

What are the key determinants for disease?

A
  • The RISK FACTORS causing the problem that can be MODIFIED on this premises
  • Ex. adequate bedding and crowding, nutritional deficiencies, inadequate dam immunizations
48
Q

Create a list of action items

A
  • Be very specific
  • Recommendations must be appropriate for INDIVIDUAL HERD MANAGEMENT
49
Q

Follow up and report to herd owner

A
  • Written report
    o Include only MOST important info
    o Write for you INTENDED audience
  • *include plans for follow-up
  • Wont always be an obvious answer
  • *keep records for a minimum of 7 years (some cases go to court)
50
Q

What are the 11 steps to a herd investigation?

A
  1. Minimize further losses
  2. Listen to the story
  3. Show me
  4. Define groups to ID risk factors
  5. Develop a hypothesis
  6. Take appropriate samples
  7. Examine animals
  8. Evaluate your hypothesis using herd records and diagnostic findings
  9. Draw up an action list
  10. Give action list to farmer, discuss hypothesis and make sure they know what to do
  11. Follow up
51
Q

What can you look at for herd fertility?

A
  • Pregnancy rate
  • Abortions
52
Q

Neosporosis abortion storm and increased risk

A
  • Seropositive cows: 6-11x more likely to be open
  • *ruled out other pathogens
53
Q

When and where did Neospora infection enter the herd?

A
  • Vertical transmission important? NO associated between cows and their dams
  • *Environmental source
    o No difference between pastures
    o *epidemic curve supported a POINT SOURCE (fence line or a mineral mix)
54
Q

Follow up to try and figure out where Neosporia came from

A
  • did precolostral blood samples
    o 64% seropositive
    o 82% born from positive cows were positive at birth
  • *only culled the seropositive that actually aborted (not feasible to get rid of them all, and it worked out for them)
55
Q

Recommendation for control of Neospora?

A
  • Proper carcass disposal
  • Minimize access of dogs to cattle feed and feed storage areas
  • Raised salt and mineral feeders on pasture
  • Test and culling of positive herd replacements (is it even practical?)
  • *complicated and many more questions than answers on it!

EVIDENCE BASED MEDICINE - 2 (6 decks)

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