guide for laboratory diagnosis in herd problem investigations

8/14/2019 Guide for Laboratory Diagnosis in Herd Problem Investigations

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Guide forGuide for

LaboratoryLaboratoryDiagnosis in HerdDiagnosis in Herd

ProblemProblemInvestigationsInvestigationsDr.Kedar KarkiDr.Kedar Karki

Senior Vet.OfficerSenior Vet.OfficerCentral Vet.LaboratoryCentral Vet.Laboratory

TripuresworTripureswor


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Logical Components of HerdL

ogical Components of HerdProblem InvestigationsProblem Investi

gations::

The unique strength of herdinvestigation is that because theindividuals are grouped into a herd.

you can compare affected animals,both clinical and subclinical, withunaffected animals, in both a cross-section (at one point in time) andover time to determine thedifferences between both the animalsthemselves and the factors affectingthem.


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GoalsGoals

Provide examples of how a variety oflaboratory diagnostic techniques areused in investigational outbreak

settings.


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Laboratory diagnosis can beLaboratory diagnosis can beused to:used to:

identify the agent causing anoutbreak;

confirm cases in an outbreak;

link cases to the same outbreak,even with cases that occur over wide

geographic areas; identify the strain or serotype of an

agent involved in an outbreak; and


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Laboratory diagnosis can beLaboratory diagnosis can beused to:used to:

Each of these uses for laboratorydiagnostics is illustrated below using anoutbreak example.

Keep in mind that the list is not exclusive.Each of these examples may featuremultiple aspects of laboratory diagnosis,

and innumerable other outbreaks couldillustrate the same points.

b d bL i i


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Laboratory diagnosis can beLa oratory iagnosis can eused to:used to:

learn more about the epidemiologyof infectious agents for researchpurposes (such as to identify new

modes of transmission, to learn moreabout newly described or reemerginginfectious diseases, or to evaluate

prevention measures).


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identify the agent causing anidentify the agent causing anongoing or recent outbreak.ongoing or recent outbreak.

Correctly identifying the agent mayallow more effective prevention.


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In 1998-1999, 3 clusters of febrileencephalitis in Malaysia were reported tothe Malaysian Ministry of Health. (1) By

the end of the outbreak, there had beenmore than 200 cases and more than 100deaths. During the same time period, 9similar cases were reported in Singapore,

including 1 death.


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Japanese Encephalitis (JE), a viralencephalitis transmitted through thebite of a mosquito, was endemic to

the area.


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Investigators initially suspected theJE virus as the cause of theoutbreak, and some specimens

tested positive for this agent.However, when nervous systemspecimens were grown in tissue

culture, a previously unknown virusgrew.


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Identifying the AgentIdentifying the AgentCausing an OutbreakCausing an Outbreak

Cases mostly adult men with swinecontact JE not usually associated with swine, so JE less

plausible

Samples from 13 patients sent to CDC fortesting JE identified from only 1 specimen

Samples then examined under an electronmicroscope; structure of similar in shape to aparamyxovirus

Additional laboratory tests performed


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Virus found to be related to Hendravirus (first identified in Hendra,Australia)

Tissues from deceased patients wereantibody positive

Antibodies also found in the serum of

some patientsVirus itself found in tissues of other

patients


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Similar investigations performedamong swine to examineepidemiologic link

Virus found in the central nervoussystem, lung, kidney tissues from swineat affected farms in Malaysia

Singapore cases handled swine fromMalaysia


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To prevent further infection:

Transport of swine within Malaysiabanned

Use of personal protective measures(gloves, masks, etc.) encouraged forswine workers

Importation of swine from Malaysiaprohibited by neighboring countries


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Research on epidemiology andtransmission of virus amongswine and humans ongoing


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outbreak investigation flow diagram below.


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1;A Problem is Detected1;A Problem is Detected

A farm event triggers the investigation.The event can be dramatic, such as aseries of unexpected deaths or a sudden,

dramatic production declines, or it can befinally the recognition of a chronic problemthat has been occurring for some time.

The earlier problems are detected,

generally the more successful theinterventions.


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1;A Problem is Detected1;A Problem is Detected

He who detects the problem isoften called on to solve it


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The three types of problemsThe three types of problemsareare

1;Acute: The problem wasprecipitated by a temporally-associated management or

husbandry error of sufficientmagnitude to be a sole cause of theproblem.


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2;Additive or Cyclic: The problem wasprecipitated by a combination ofmanagement or husbandry errors over

time and the effects of cyclical factorssuch as season or production cycle stagessuch that the combination was sufficient toprecipitate the problem. Ex: the summer

coliform mastitis outbreak that isassociated with the previous winterchange to sawdust bedding.


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3:Chronic: The problem wasprecipitated by the long action ofmanagement or husbandry errors

that required the passage of time forbefore the consequences became ofsufficient magnitude to berecognized, such as the slow spread

of a contagious mastitis agent or ofMycobacterium paratuberculosis.


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Ex: the recognition of a Staph.aureus mastitis problem associatedwith the adoption of a less efficacious

teat dipping procedure more than ayear previously.

2 Establish o Ve if the2:Establish or Verify the


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2:Establish or Verify the2:Establish or Verify thePathological and EtiologicalPathological and Etiological

DiagnosisDiagnosis

If the diagnosis is not definitive and if oneis needed, start the process to obtain adefinitive pathologic and etiologic

diagnosis by collecting samples andsubmitting these to diagnosticlaboratories. If dead or dying animals areinvolved, have complete field necropsies

been done of a sufficient number ofrepresentative animals?


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Epidemiologic Triad ofEpidemiologic Triad ofDiseaseDisease

Host

EnvironmentAgent


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The Natural History ofThe Natural History ofDiseaseDisease

Outcome

Cure

Control

Disability

Death

Disease Symptoms Seek Diagnosis Treatment

Onset Care

Healthy


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3:Establish a Case3:Establish a CaseDefinitionDefinition

Establish a case definition, precise asreasonable, to exclude those cases thatare due to endemic background problems.

You may wish to establish a case definitionwith different degrees of certainty (e.g.,certainly affected, possibly affected,possibly unaffected, certainly unaffected).

Remember the iceberg principle andthe spectrum of disease.

d M it d f thd M it d f th
http://www.vetmed.wsu.edu/courses-jmgay/EpiMod2.htmhttp://www.vetmed.wsu.edu/courses-jmgay/EpiMod2.htmhttp://www.vetmed.wsu.edu/courses-jmgay/EpiMod2.htmhttp://www.vetmed.wsu.edu/courses-jmgay/EpiMod2.htm


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and Magnitude of theand Magnitude of theProblem with ObjectiveProblem with Objective

DataData Obtain objective data to

document and verify the

magnitude of the problem; donot rely only on the memoriesand perception of managementand employee .

Remember: More mistakes aremade from not looking than fromnot knowing!


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Problem with ObjectiveProblem with ObjectiveDataData

A:Establish the Timing of theproblem (the temporal pattern -When?)

B:Establish the Place of theproblem (the spatial pattern -Where?)

C:Establish the Demographics ofaffected vs. non-affected animals(Who?)


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5:Assemble and Analyze5:Assemble and Analyzethe Datathe Data

For an outbreak, establish anepidemic curve.

For endemic problems, plot risk overtime by cohort group.

Examine the effects of other factorsthat vary over time


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(Differential Diagnoses)(Differential Diagnoses)about Key Determinantsabout Key Determinants

Key determinants are those riskfactors causing the problem thatcan be modified on this premises.


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7:Test Your Hypotheses7:Test Your Hypotheses

Make predictions of the form "ifthis cause is present, then thisfinding should be present".


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8:Design Interventions8:Design Interventionsand/or Prospective Studiesand/or Prospective Studies

Generate action items that arecompatible with the specific facilities,economic limitations and

management scheme of thepremises.


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9:Report Your Findings9:Report Your Findings

"The faintest pen is stronger thanthe strongest mind" and that"Success has many fathers but

failure is an orphan." If yourrecommendations are successful,because of the passage of time youwill not likely get the credit due you

unless they were documented.

0 i l f10 M it R lt f


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10:Monitor Results of10:Monitor Results ofInterventionsInterventions

Develop a monitoring scheme toprovide early warning of theproblem. If the herd doesn't have a

good production accounting systemto monitor changes in production butone is warranted, propose one.


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Investigation ExecutionInvestigation Execution::

1:Record the physical layout ofpremises.

2:Record the current numbers of

animals in each pen or area andthe intended maximum capacityof these areas.

3:Record the animal "calendar"intended by management for therelevant animals


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SummarySummary

tests can be used to: Solve outbreak investigations Identify agents Investigate remaining questions about

infectious diseases Laboratory diagnostic techniques are an

integral part of public health surveillance,investigation, and research

Understanding the basics of how thesetests work will improve your conduct ofoutbreak investigations


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guide for laboratory diagnosis in herd problem investigations

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