Assessing the probability of introduction and spread of avian influenza (AI) virus in commercial Australian poultry operations using an expert opinion elicitation.

Mini Singh,Peter Groves,Amanda Black,Kathryn Glass,Belinda Barnes,Jenny-Ann Toribio,Marta Hernandez-Jover,Angela Bullanday Scott,Barbara Moloney

doi:10.1371/journal.pone.0193730

Abstract

The objective of this study was to elicit experts’ opinions and gather estimates on the perceived probability of introduction and spread of avian influenza (AI) virus in the Australian broiler and layer industry. Using a modified Delphi method and a 4-step elicitation process, 11 experts were asked to give initial individual estimates for the various pathways and practices in the presented scenarios using a questionnaire. Following this, a workshop was conducted to present group averages of estimates and discussion was facilitated to obtain final individual estimates. For each question, estimates for all experts were combined using a discrete distribution, with weights allocated representing the level of expertise. Indirect contact with wild birds either via a contaminated water source or fomites was considered the most likely pathway of introduction of low pathogenic avian influenza (LPAI) on poultry farms. Presence of a water body near the poultry farm was considered a potential pathway for introduction only when the operation type was free range and the water body was within 500m distance from the shed. The probability that LPAI will mutate to highly pathogenic avian influenza (HPAI) was considered to be higher in layer farms. Shared personnel, equipment and aerosol dispersion were the most likely pathways of shed to shed spread of the virus. For LPAI and HPAI spread from farm to farm, shared pick-up trucks for broiler and shared egg trays and egg pallets for layer farms were considered the most likely pathways. Findings from this study provide an insight on most influential practices on the introduction and spread of AI virus among commercial poultry farms in Australia, as elicited from opinions of experts. These findings will be used to support parameterization of a modelling study assessing the risk of AI introduction and spread among commercial poultry farms in Australia.

Highlights

The primary source of avian influenza (AI) virus introduction into commercial poultry is believed to be from aquatic wild bird reservoirs [1,2,3,4], the mechanisms of its introduction and subsequent spread have not been fully elucidated
The current study aimed to investigate the pathways of AI introduction and spread and the corresponding probabilities of these pathways, using an expert opinion exercise with a modified Delphi technique and a 4-step elicitation procedure [29] on different types of broiler and layer production operations
Of the various pathways, shared bird pick up transport was considered to be most likely pathway of spread from broiler farms for both low pathogenic avian influenza (LPAI) (27.3%; 11.6–61.1% for broiler barn (BB) and 29.7%; 12.0–63.6% for broiler free range (BFR)) and highly pathogenic avian influenza (HPAI) (21.1%; 4.1–46.8% for BB and 20.2%; 3.3–48.1% for BFR), while shared egg trays (24%; 4.3–42.8% each for layer cage (LC), layer barn (LB) and layer free range (LFR) for LPAI and 22.4%; 8.0–47.4% for LC, 21.8%; 8.1–49.9% for LB and 22.1%; 8.0–54.3% for LFR for HPAI) and pallets (16%; 4.32–36.4% each for LC, LB and LFR for LPAI and 9.7%; 4.4–41.7% for LC, 11.4%; 4.1–50.0% for LB and 11.1%; 4.4–48.3% for LFR for HPAI) were considered to be most likely pathways for the layer operations (Fig 5)

Summary

Introduction

The primary source of avian influenza (AI) virus introduction into commercial poultry is believed to be from aquatic wild bird reservoirs [1,2,3,4], the mechanisms of its introduction and subsequent spread have not been fully elucidated. Australia has had seven highly pathogenic avian influenza (HPAI) outbreaks on chicken farms during the last 32 years, four of which have occurred in the last 10 years, suggesting that the frequency of outbreaks is increasing In these past seven HPAI outbreaks in Australia, involving a total of 12 farms, all viruses were of subtype H7 and of Australian lineages but the definite mechanisms for spread between farms were not identified. Both H5 and H7 low pathogenic avian influenza (LPAI) viruses, which have the potential to mutate into HPAI, are endemic in wild birds of Australia [11]. It is believed that AI virus outbreaks in Australia occur via endemic LPAI exposure following contact with wild birds and mutation to HPAI on poultry farms

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