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

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

2

Release Pathway for the Potential Movement of HPAI Infected Birds

3

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

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

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

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

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

7

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

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

8

Pooled sample with 5 or 11 swabs from dead birds Disease

Mortality

HPAI detected via rRT-PCR testing

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

9

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

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

10

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

11

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)%

12

Predicted likelihood of a broiler flock (house) being infected and undetected at movement from simulation results (conservative approach)

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

13

0

1

2

3

4

5

6

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

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

14

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

15

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

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

17

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.

18

Questions?

19

Sasidhar Malladi, PhD malla042@umn.edu University of Minnesota Center for Animal Health and Food Safety, St. Paul, Minnesota

Todd Weaver, DVM Dip ACVPM todd.weaver@aphis.usda.gov USDA-APHIS-VS-STAS Center for Epidemiology and Animal Health, Fort Collins, Colorado

mailto:malla042@umn.edumailto:todd.weaver@aphis.usda.gov

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?