Evaluating the risk of avian influenza introduction and spread among poultry exhibition flocks in Australia.

Some practices undertaken by poultry exhibitors, such as allowing wild birds to contact domestic birds, the high frequency of bird movements and the lack of appropriate isolation for incoming birds, pose a risk for disease introduction and spread. The aim of the current study was to quantitatively assess the probability of introduction of low pathogenic avian influenza (LPAI) viruses from wild waterfowl into poultry exhibition flocks and the subsequent spread to other poultry flocks. Exposure and consequence assessments, using scenario trees and Monte Carlo stochastic simulation modelling, were conducted to identify potential pathways of introduction and spread and calculate the probabilities of these pathways occurring. Input parameters were estimated from two recently conducted cross-sectional studies among poultry exhibitors in Australia (Dusan et al., 2010; Hernández-Jover et al., 2013) and other scientific literature. According to reported practices of poultry exhibitors and the LPAI prevalence in wild birds in Australia, this assessment estimates a median (5-95%) probability of exposure of a bird kept by a poultry exhibitor of 0.004 (0.003-0.005). Due to the higher susceptibility of infection of turkeys and waterfowl, this probability is higher in flocks keeping these bird species than in those keeping chickens or pigeons only. Similarly, once exposure has occurred, establishment of infection and subsequent spread are more likely in those flocks keeping waterfowl and turkeys than in those keeping chicken and pigeons only. Spread through movement of birds is the most likely pathway of spread, followed by contaminated fomites, wild birds and airborne spread. The median probability of LPAI spread through movement of birds in flocks keeping waterfowl and turkeys was estimated to be 0.280 (0.123-0.541) and 0.230 (0.104-0.421), respectively. A lower probability was estimated for chicken (0.087; 0.027-0.202) and pigeon (0.0003; 3.0×10(-5)-0.0008) flocks. The sensitivity analysis indicates that the prevalence of LPAI in wild waterfowl and the probability of contact of domestic birds with wild waterfowl are the most influential parameters on the probability of exposure; while the probability of spread is mostly influenced by the probability of movement of birds and the probability of the exhibitor detecting and reporting LPAI. To minimize the potential risk of AI introduction and spread, poultry exhibitors should prevent contact of domestic birds with wild birds, and implement appropriate biosecurity practices. In addition, adequate extension services are required to improve exhibitors' abilities to recognize diseases and reporting behaviour.