Avian influenza risk assessment for the Australian commercial chicken industry

Abstract

The rapid expansion of commercial free range chicken farms in Australia has caused concern among industry experts that contact between wildlife and commercial chicken flocks will increase, therefore leading to increased exposure to low pathogenic AI (LPAI) virus from wild birds and subsequent mutation within the chicken flocks to high pathogenic avian influenza (HPAI). The probabilities involved with chickens being exposed to LPAI virus, the occurrence of subsequent spread of both LPAI and HPAI, as well as features or practices on farm that could mitigate the risks were largely unknown. This thesis describes the conduct of a farm survey and wildlife camera trapping to describe features related to farm design, management practices, biosecurity practices and wildlife visits on Australian commercial chicken farms, specifically; 15 non-free range meat chicken farms, 15 free range meat chicken farms, nine cage layer farms, nine barn layer farms and 25 free range layer farms in the Sydney basin bioregion and South East Queensland. It then describes the development, evaluation and sensitivity analysis of exposure and partial consequence risk assessment models using inputs from the farm survey, scientific literature and expert opinion to assess the risk of exposure and spread of LPAI and HPAI among these commercial chicken farm types in the Australian context. The exposure risk assessment model investigated the pathways of exposure of Australian commercial chicken farms to LPAI virus from Australian wild birds and estimated the probability of exposure occurring using scenario trees and a stochastic modelling approach. The partial consequence assessment following the exposure risk assessment model investigated the likelihood of spread of LPAI and HPAI without quantifying the impact of the consequences of spread within and between Australian commercial chicken farms.