Risk Assessment of HPAI Spread via Movement of Broilers to … · 2017. 10. 23. · Stochastic...
Transcript of Risk Assessment of HPAI Spread via Movement of Broilers to … · 2017. 10. 23. · Stochastic...
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Risk Assessment of HPAI Spread via Movement of Broilers to Processing
Sasidhar Malladi a, J. Todd Weaver b, Minden Buswell a, Jamie Slingluff a, Catherine Alexander a, Timothy Goldsmith a, David Halvorson a
a University of Minnesota, Center for Animal Health and Food Safety b USDA Animal and Plant Health Inspection Service, Veterinary Services, Science
Technology and Analysis Services, Center for Epidemiology and Animal Health
AAAP 2014 Annual Meeting Denver, Colorado, July 28, 2014
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Introduction
Risk assessment for HPAI spread via movement of broilers to processing
• Evaluates potential movement of infected and undetected flocks
• Considers current practices and outbreak measures
• Supports risk management and further on-scene evaluation in an outbreak
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Release Pathway for the Potential Movement of HPAI Infected Birds
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Step 1: Premises in Control Area becomes
infected
Vehicles, people, i.e. local area spread
Mitigation for Step 1: Biosecurity and distance Step 2: HPAI infection is not detected before movement
Mitigation for Step 2: Active surveillance
Possible movement of HPAI infected birds
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Dead
Infectious
Impact of Pre-movement Isolation Period (PMIP)
Exposure to HPAI
several days before movement
Scheduled movement
date
If the house is infected several days before movement, it
would likely be detected via active
surveillance.
4 Timeline Days
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Impact of Pre-movement Isolation Period (PMIP)
Scheduled movement
date
Dead
InfectiousExposure to HPAI close to
Movement
The disease prevalence and the
likelihood of detecting before movement
would be lower than if exposure is earlier.
5 Timeline Days
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Dead
Infectious
Impact of Pre-movement Isolation Period (PMIP)
Exposure to HPAI
several days before movement
Scheduled movement
date
Start of PMIP
If the house is infected several days before movement, it
would likely be detected via active
surveillance.
Exposure risk close to the time of movement is reduced by
PMIP biosecurity
6 Timeline Days
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Methods: Disease Transmission Model
Stochastic chain binomial disease transmission model
• Simulates spread of HPAI among birds in a house
• Predicts susceptible, latent, infectious and dead birds over time
• Considerable uncertainty in parameters such as effective contact rate, infectious and latent periods
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0
5,000
10,000
15,000
20,000
25,000
0 2 4 6 8 10
Num
ber o
f Bird
s
Days post Infection of the house
Susceptible latent infectious Dead
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Normal Mortality
Methods: Active Surveillance Model
Active surveillance model simulates detection of HPAI • Chances of a swab from a diseased bird being included in the
pooled sample taken randomly from daily mortality • Detecting a virus positive pooled sample given diagnostic
sensitivity • Considers the variability in normal and disease mortality
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Pooled sample with 5 or 11 swabs from dead birds Disease
Mortality
HPAI detected via rRT-PCR testing
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Scenario Pooled sample size for testing
dead birds
HPAI Strain
5 swabs H5N2
11 swabs H5N2
5 swabs H5N1
11 swabs H5N1
Probability of Detecting HPAI Under Various Pre-movement Isolation Period (PMIP) Durations
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0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
2 3 4 5 6
Prob
abili
ty o
f Det
ecti
on
Pre-movement Isolation Period (Days)
Simulation results on detection probability if the flock became exposed before PMIP
Active surveillance options: testing a pooled sample on two consecutive days before movement with rRT-PCR
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The Likelihood of a Premises Becoming Infected with HPAI
• Quantitative spatial analysis • Transmission parameters estimated in literature are for all
spread mechanisms combined • Provides conservative estimates of the likelihood of spread
compared to when PMIP measures are followed
• Qualitative assessment • Individual pathways are evaluated: critical operational
visits (e.g., feed delivery, repairmen), dead bird disposal, farm personnel, wildlife, insects, and aerosol
• Impact of PMIP biosecurity measures • Literature review, outbreak reports and expert opinion
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Likelihood of Exposure of a Poultry Premises as a Function of Distance From an HPAI Infected Premises Based on Spatial
Transmission Models
0.00%
0.20%
0.40%
0.60%
0.80%
1.00%
1.20%
0.5 1.5 2.5 3.5 4.5 5.5
Dai
ly L
ikel
ihoo
d of
Exp
osur
e
Distance From an HPAI Infected Poultry Premises (km)
Dorigatti et al.(2010) Italy H7N1
Boender et al.(2007) NetherlandsH7N7Rorres et al. (2011)Pennsylvania H5N2
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Quantitative Simulation Results on the Likelihood of a Flock (1) Becoming Infected with HPAI Virus and
(2) Moving Infectious Birds Before Detection
rRT-PCR pooled sample sizes of 11 or 5 dead birds (in parentheses) with testing on two consecutive days before movement were evaluated
Distance from an infected
premises (km)
Spatial transmission model used
Dorigatti (2010) Italy HPAI H7N1
Boender (2007) Netherlands HPAI H7N7
Rorres (2011) Pennsylvania HPAI H5N2
1.5 1.10(1.25)% 0.34(0.38)% 0.14(0.24)% 2 0.88(1.0)% 0.26(0.29)% 0.01(0.13)% 3 0.55(0.63)% 0.15(0.17)% 0.00(0.05)% 5 0.25(0.28)% 0.06(0.07)% 0.00(0.02)%
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Predicted likelihood of a broiler flock (house) being infected and undetected at movement from simulation results (conservative approach)
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Qualitative Evaluation: Likelihood of Transmission via Feed Delivery
• A risk factor in some outbreak
studies • Odds ratio was not large
• Driver biosecurity and vehicle
C&D • Driver not entering the
henhouse • Effectiveness of PPE
protocols with footwear, gloves and hand hygiene
• Likelihood of transmission was rated to be negligible to low given Secure Broiler Supply plan measures
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1
2
3
4
5
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RoutineBiosecurity
OutbreakBiosecurity
Num
ber
of r
espo
nses
(out
of 8
)
Expert opinion on feed movement as a risk factor for introducing HPAI (by veterinarians with field AI experience)
extremely high
high
moderate
low
negligible
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Exposure Assessment
• Estimates the likelihood of susceptible poultry becoming exposed to HPAI due to movement of broilers
• Likelihood of moving infectious birds was rated to be negligible to low when the premises is 2-3 km from infected premises, given PMIP biosecurity and active surveillance
• Potential exposure pathways include • Manure, dust or feathers to premises on route • Load out crew, equipment or live haul vehicles • Plant employees, waste water • Offal movement from processing plants
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Live Haul and Load Out Equipment Exposure Pathway
Step1: Previous farm was infected and undetected at load out Conservative quantitative estimates: Likelihood of 0.0005-0.01 per movement, 2-3 km from infectious premises Qualitative evaluation: negligible to low likelihood, 2-3 km from infected premises
Step2: HPAI Virus is introduced into a house on another premises at next load out Step 3: Virus is
not inactivated during downtime
Step 4: Next flock introduced into the house becomes infected
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Live Haul And Load Out Equipment Exposure Pathway (Impact of Downtime)
• In rare cases, when release occurs, 31 (90% P.I., 1-135) infectious birds were predicted to be present in a house with 24,300 birds
• Impact of extended down time (21 days) or heating to 40.6°C for 2 days
• Preheating floor temperature (usually 85-95°F for 24 hours)
• Non-brooding areas are not
utilized for 1 to 2 weeks
d
d d d
d
d
u
u u
u
h
h h
w
w
w w w w
w w
w
w
w w
w
w
0
5
10
15
20
25
30
35
40
0 10 20 30 40
Tem
pera
ture
°C
Time Days w-wet, d-dry, h-high relative humidity, u-unknown
humidity/moisture
Data on inactivation of AI in feces from literature review
Dry orunknown
Humid orwet
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Preliminary Results
Release or exposure assessment pathway step (following SBS measures )
Qualitative likelihood ratings
Broiler premises 2 km
from IP
Broiler premises 3 km
from IP
Broiler flock is infected and undetected at movement (release)
Low
Negligible to low
Release occurs and susceptible poultry become exposed to HPAI via live haul or load out equipment
Negligible to low
Negligible
Release occurs and susceptible poultry flocks adjacent to the route become exposed (1000 m away from road)
Negligible
Negligible
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Conclusion
• Active surveillance, pre-movement biosecurity and distance from infected premises can provide confidence that HPAI infected and undetected broilers are not moved to processing.
• Secure Broiler Supply measures such as complete load out and vehicle routing would further limit HPAI spread to susceptible poultry.
• Proactive risk assessment supports the managed movement of broilers by providing scientific evaluation to inform movement permitting decisions and emergency response planning.
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Questions?
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Sasidhar Malladi, PhD [email protected] University of Minnesota Center for Animal Health and Food Safety, St. Paul, Minnesota
Todd Weaver, DVM Dip ACVPM [email protected] USDA-APHIS-VS-STAS Center for Epidemiology and Animal Health, Fort Collins, Colorado
mailto:[email protected]:[email protected]
Risk Assessment of HPAI Spread via Movement of Broilers to ProcessingIntroduction Release Pathway for the Potential Movement�of HPAI Infected BirdsImpact of Pre-movement Isolation Period (PMIP)Impact of Pre-movement Isolation Period (PMIP)Impact of Pre-movement Isolation Period (PMIP)Methods: Disease Transmission ModelMethods: Active Surveillance ModelProbability of Detecting HPAI Under Various Pre-movement Isolation Period (PMIP) DurationsThe Likelihood of a Premises Becoming Infected with HPAI Likelihood of Exposure of a Poultry Premises as a Function of Distance From an HPAI Infected Premises Based on Spatial Transmission ModelsQuantitative Simulation Results on the Likelihood of a Flock (1) Becoming Infected with HPAI Virus and �(2) Moving Infectious Birds Before DetectionQualitative Evaluation: Likelihood of Transmission via Feed DeliveryExposure AssessmentLive Haul and Load Out Equipment Exposure PathwayLive Haul And Load Out Equipment Exposure Pathway (Impact of Downtime)Preliminary ResultsConclusionQuestions?