Simulating Risk Reduction Using Biosecurity Practices on Farm

Abstract. Farm-level biosecurity needs to consider the movement of multiple individuals, equipment and supplies among various places over time. The points in space or time where movements intersect are risk points for pathogen transmission. Biosecure entry and exit practices employed on a farm influence these risk points. We developed a model to simulate the transfer of particles by humans moving around on poultry and other livestock farms. Particles can include pathogenic particles (such as bacteria, viruses) and inert particulate (such as dander, dust and feed particles). The model assumptions include: humans are the only vectors for particle movement around a farm; humans and places on a farm possess a fixed number of particles; and the chance of loss or gain of particulates relates to the time and surface area of the human that touches or interacts with a place or area. The model uses a specified daily routine of movement by one or more workers among multiple places on a farm. Particles transfer between workers and places using replace events (i.e. worker particles are removed from the system and replaced with inert particles during a biosecure entry event), or swap events (i.e. barn particles replace worker particles and vice versa during barn chores). A randomization process in the model dictates whether pathogenic particles transfer along with inert particles during any event, lending variability to the model results. We explore how combinations of pathogen source, pathogen concentration of the source, biosecure entry/exit practices, and sequence of events influence the risk of pathogenic particles ending up in barns, on workers or other places around a multi-barn poultry site. The intention of the model is to provide farms and organizations opportunity to assess and enhance biosecurity plans and communication strategies.