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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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identify the agent causing anidentify the agent causing anongoing or recent outbreak.ongoing or recent outbreak.
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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identify the agent causing anidentify the agent causing anongoing or recent outbreak.ongoing or recent outbreak.
Japanese Encephalitis (JE), a viralencephalitis transmitted through thebite of a mosquito, was endemic to
the area.
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identify the agent causing anidentify the agent causing anongoing or recent outbreak.ongoing or recent outbreak.
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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Identifying the AgentIdentifying the AgentCausing an OutbreakCausing an Outbreak
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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Identifying the AgentIdentifying the AgentCausing an OutbreakCausing an Outbreak
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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Identifying the AgentIdentifying the AgentCausing an OutbreakCausing an Outbreak
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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Identifying the AgentIdentifying the AgentCausing an OutbreakCausing an Outbreak
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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The three types of problemsThe three types of problemsareare
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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The three types of problemsThe three types of problemsareare
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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33
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.htm8/14/2019 Guide for Laboratory Diagnosis in Herd Problem Investigations
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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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