“…In addition to direct contact among farms via animal movements, indirect contact may occur between farms due to windborne propagation of aerosols and dissemination of fomites by personnel, contaminated vehicles, and feed (Alonso et al, 2014;Alvarez et al, 2016;Beam et al, 2015;Dee et al, 2014;Kim et al, 2017;Lowe et al, 2014;O'Dea et al, 2015;Pasick et al, 2014). Although the potential importance of such mechanisms in creating transmission opportunities between swine premises has been shown in experimental studies and outbreak investigations (Alonso et al, 2014;Bowman et al, 2015;Lowe et al, 2014;Pasick et al, 2014), indirect contact is less often accounted for in epidemiological models (Arruda et al, 2016;Martinez-Lopez et al, 2011;Thakur et al, 2015;Yadav et al, 2016). Models of pathogen spread in livestock populations focus primarily on animal movement and, in some cases, local spatial spread based on proximity between premises (Brooks-Pollock et al, 2015).…”