Data_Sheet_1_Low Pathogenic Avian Influenza Exposure Risk Assessment in Australian Commercial Chicken Farms.docx

This study investigated the pathways of exposure to low pathogenic avian influenza (LPAI) virus among Australian commercial chicken farms and estimated the likelihood of this exposure occurring using scenario trees and a stochastic modeling approach following the World Organization for Animal Health methodology for risk assessment. Input values for the models were sourced from scientific literature and an on-farm survey conducted during 2015 and 2016 among Australian commercial chicken farms located in New South Wales and Queensland. Outputs from the models revealed that the probability of a first LPAI virus exposure to a chicken in an Australian commercial chicken farms from one wild bird at any point in time is extremely low. A comparative assessment revealed that across the five farm types (non-free-range meat chicken, free-range meat chicken, cage layer, barn layer, and free range layer farms), free-range layer farms had the highest probability of exposure (7.5 × 10−4; 5% and 95%, 5.7 × 10−4—0.001). The results indicate that the presence of a large number of wild birds on farm is required for exposure to occur across all farm types. The median probability of direct exposure was highest in free-range farm types (5.6 × 10−4 and 1.6 × 10−4 for free-range layer and free-range meat chicken farms, respectively) and indirect exposure was highest in non-free-range farm types (2.7 × 10−4, 2.0 × 10−4, and 1.9 × 10−4 for non-free-range meat chicken, cage layer, and barn layer farms, respectively). The probability of exposure was found to be lowest in summer for all farm types. Sensitivity analysis revealed that the proportion of waterfowl among wild birds on the farm, the presence of waterfowl in the range and feed storage areas, and the prevalence of LPAI in wild birds are the most influential parameters for the probability of Australian commercial chicken farms being exposed to avian influenza (AI) virus. These results highlight the importance of ensuring good biosecurity on farms to minimize the risk of exposure to AI virus and the importance of continuous surveillance of LPAI prevalence including subtypes in wild bird populations.

本研究针对澳大利亚商业养鸡场的低致病性禽流感（low pathogenic avian influenza, LPAI）病毒暴露途径展开调查，并参照世界动物卫生组织（World Organization for Animal Health）的风险评估框架，采用情景树与随机建模方法，估算该类暴露事件的发生概率。模型的输入参数来源于公开科学文献，以及2015至2016年间针对澳大利亚新南威尔士州与昆士兰州境内商业养鸡场开展的实地农场调查。模型输出结果显示：任意时段内，单只野生鸟类导致澳大利亚商业养鸡场鸡只首次暴露于LPAI病毒的概率极低。对比五类养鸡场（非散养肉用鸡场、散养肉用鸡场、笼养蛋鸡场、舍养蛋鸡场及散养蛋鸡场）的暴露风险后发现，散养蛋鸡场的暴露概率最高（7.5×10⁻⁴；5%分位数与95%分位数区间为5.7×10⁻⁴—0.001）。研究结果表明，所有农场类型的病毒暴露均需以农场内存在大量野生鸟类为前提。直接暴露的中位概率在散养型鸡场中最高：散养蛋鸡场与散养肉用鸡场分别为5.6×10⁻⁴与1.6×10⁻⁴；而间接暴露的中位概率则在非散养型鸡场中最高：非散养肉用鸡场、笼养蛋鸡场及舍养蛋鸡场依次为2.7×10⁻⁴、2.0×10⁻⁴与1.9×10⁻⁴。所有农场类型的病毒暴露概率均在夏季处于最低水平。敏感性分析结果显示，农场野生鸟类中水禽的占比、活动范围与饲料储存区域内水禽的存在情况，以及野生鸟类种群中LPAI的流行率，是影响澳大利亚商业养鸡场暴露于禽流感（avian influenza, AI）病毒概率的最具影响力的参数。本研究结果凸显了强化农场生物安全以降低AI病毒暴露风险的重要性，同时也强调了持续监测野生鸟类种群中LPAI流行率及其亚型的必要性。