Population viscosity suppresses disease emergence by preserving local herd immunity

Animal reservoirs for infectious diseases pose ongoing risks to human populations. In this theory of zoonoses, the introduction event that starts an epidemic is assumed to be independent of all preceding events. However, introductions are often concentrated in communities that bridge the ecological interfaces between reservoirs and the general population. In this paper, we explore how the risks of disease emergence are altered by the aggregation of introduction events within bridge communities. In viscous bridge communities, repeated introductions can elevate the local prevalence of immunity. This local herd immunity can form a barrier reducing the opportunities for disease emergence. In some situations, reducing exposure rates counterintuitively increases the emergence hazards because of off-setting reductions in local immunity. Increases in population mixing can also increase emergence hazards, even when average contact rates are conserved. Our theory of bridge communities may help guide prevention and explain historical emergence events, where disruption of stable economic, political or demographic processes reduced population viscosity at ecological interfaces.

Supporting Situation Awareness Through Ecological Interface Design

A full-scope simulation study with licensed nuclear power plant operators was conducted to evaluate whether displays designed using Ecological Interface Design (EID) could support improved Situation Awareness over traditional displays. EID demonstrated performance advantages over traditional displays in beyond-design basis scenarios where operators were unable to rely on procedures. The same effects were not seen in within-design basis scenarios where procedures were available. This suggests that EID has the potential to improve SA in unanticipated situations, but that ecological interfaces should be supported with task-based displays in procedure-driven situations.