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How to approach a respiratory disease outbreak on a livery yard

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How to approach a respiratory
disease outbreak on a livery yard
BEVA Congress 2012
Thursday 13th 0830-0855
Philip Ivens
MA VetMB CertEM (Int.Med.) DipECEIM MRCVS
European Specialist in Equine Internal Medicine
Outbreak toolbox
Information
Prevention
Communication
Control the outbreak
Diagnostic tests
Taking advice
Livery Yard – Unique challenges
• Diverse and individual owners
• Conflicting interests and economic status
• Key for message to be clear and simple
• Key for multi-vet yards to work together
• Yard owner/manager central to this.
Outline
• Disease situation – local and national/international
• Differentials Diagnoses
• Clinical Signs
• Diagnostic Tests
• Biosecurity
Disease Situation Locally
• Local knowledge/experience – internal practice
communication/team work.
• Communication between practices
• Local laboratories
Disease Situation Nationally
• Influenza Alert System - Merial
• National Laboratories – e.g. AHT.
• DEFRA/AHT/BEVA Equine Quarterly Disease Surveillance Reports
- http://www.aht.org.uk/cmsdisplay/disease_surveillance.html
• Strangles mapping – future?
Disease Situation Internationally
Endemic DDx
Viruses:
• EIV – Influenza
• EHV1,4 – Herpes
• ERV – Rhinovirus
• Adenovirus
Bacteria:
• Streptococci
•
•
•
•
S. equi subsp equi
S. equi subsp
zooepdemicus
S. dysgalactiae subsp
equisimilis
S. pneumoniae
Non-infectious:
• RAO/IAD
• Smoke inhalation
Exotic DDx
Viruses:
• EVA
• Hendra Virus
• AHS
• (Parainfluenza-3)
Bacterial:
• Glanders
Clinical Signs – Any help???
• Fever
• Nasal Discharge – mucoid→mucopurlent
• Submandibular Lymph Nodes Enlargement
• Cough
• Conjunctivitis, anorexia, depression
Clinical Signs Table
Fever
Influenza
Nasal
Discharge
SMLN
Cough
+++
2-4dys
Serous
initially
++
+++
Paroxysmal
++
Biphasic
8-10dys
Serous
initially
++
+
ERV
++
Serous
initially
++
+
EVA
++
Serous
initially
++
++
Strangles
+++
Serous to
purulent
+++
+
Strep zoo
++
Purulent
++
+
EHV1,4
Diagnostic tests
• Which animals,
which samples, which tests?
End-point analysis of
amplification product
• Interpretation?
Strangles - Culture
• Gold standard for diagnosis?
• Nasopharyngeal swabs, abscess or (GP lavage)
• β-haemolytic, Group C Gram positive cocci
• Does NOT ferment lactose, sorbitol, ribose.
• Need sufficient live bacteria for a positive - FRAGILE
PCR
• Detects nucleic acid (bacterial DNA)
• Exponential (enzyme catalysed) amplification of
target DNA sequences
• Very sensitive in ideal conditions
• Sensitivity reduced in clinical samples
• Rapid (hours) and specific
• Potentially quantative
End-point analysis of
amplification product
Interpreting Strangles PCR results
PCR
positive
PCR
negative
Culture
positive
?
?
Culture
negative
?
?
Interpreting Strangles PCR results
PCR
positive
PCR
negative
Culture
positive
Infected
Infected
Culture
negative
?
?
Interpreting Strangles PCR results
Culture
positive
Culture
negative
PCR
positive
PCR
negative
Infected
Infected
Infected
Not
infected?
Gronbaek et al, 2006 (Equine Vet J 38: 59-63)
Strangles
clinical signs
No clinical signs
of strangles
Sensitivity
Nasal swabs
Culture = 18%
PCR = 45%
Abscesses
Culture = 20%
PCR = 80%
Gronbaek et al, 2006 (Equine Vet J 38: 59-63)
Strangles ELISA
•
A antigen
• ≤0.2 0.D. - negative
• 0.3-0.4 0.D. – inconclusive
• ≥0.5 0.D. - positive
• B antigen
• C antigen
• ≤0.2 0.D. - negative
• 0.3-0.4 0.D. –
inconclusive
• ≥0.5 0.D. - positive
• ≤0.5 0.D. – negative
• 0.6-0.9 0.D. – inconclusive
• ≥1.0 O.D. - positive
• Inconclusive results need a second sample after 14 d
to determine if rising or falling titre.
ELISA interpretation
•
Antibodies can take up to 14 days to rise and stay high for at
least 6mths - ?use in acute outbreak
•
Paired serology requires re-testing of sample 2 vs sample 1
•
Inter-assay variation
•
Result and re-test В±0.3
•
Valid comparison ONLY between samples tested as pairs
i.e. A to A, B to B and C to C
Equine Influenza
• NPS – virus culture, ELISA nucleoprotein, PCR/IF
direct Ag – ACUTE PHASE – NEW CASES
• Serology – Ab’s - Haemagglutination inhibition
• > 4x increase in Ab titre between convalescent and 14dy
sample - significant
• Subclinical infections do not show 4x increase
• Single radial haemolysis – detects 2x ↑ Abs
Equine Herpes Virus 1 and 4
• NPS – Tissue culture or PCR
• Tracheal Wash – Viral Antigen – IF
• Serology
•
Compliment Fixation – short lived
•
Virus Neutralisation – long lived
•
ELISA
Economics
• Strangles
• Influenza
• Culture - £16.50
• Ag - qPCR or ELISA £25.00
• PCR - £20.50 combined £30.50
• Serology HI - £15.50, SRH- £36.00
• Serology - £27.50 all three
ВЈ50.75
• EHV1,4
• Tissue culture - £33.00
• Respiratory Viral serology screen:
•
ВЈ38.75
•
plus equi ВЈ59.00
• NPS Screen – EHV-1,4, Strep
• PCR - £45.00
equi, zoo PCR plus Flu ELISA or
• Serology – CF £20.50
qPCR - ВЈ100.00
Nasopharyngeal Swab
• Up to level medial canthus and ensure horse
swallows.
• High surface area, absorbent swab required.
Transport media
• Charcoal
• Saline
• AHT
• Green – Bacteriology plus PCR
• Pink – Influenza NOT bacteria
• White – Virology NOT bacteria
Transport Media – Top tip
• Contains antibiotic – need to be frozen
• Once sample has been taken put back in plastic
sleeve and keep in cool dark place in your car
• Cut off and place directly in media and post.
Equine Influenza Surveillance
Scheme
•
FREE to join – FREE diagnostic testing NPS & sera
•
Kits include submission form and swabs/transport media.
•
Epidemiological information gathered fed back into OIE.
•
www.equiflunet.org.uk or e-mail equiflunet@aht.org.uk
•
Informs OIE of current virus strains and feeds into vaccine
recommendations.
Biosecurity
Yard Biosecurity Poster
Take Home Messages
• Communication and team work very important
• Know the current disease state locally and nationally
• Be critical of your laboratory tests and optimise them
• Biosecurity key in preventing spread of disease
Acknowledgements
• Josh Slater – The Royal Veterinary College
• Animal Health Trust – Andrew Waller and Richard
Newton
• MSD
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