Managing the risk of wildlife disease introduction: pathway-level biosecurity for preventing the introduction of alien ranaviruses.
Alien species are key vectors for the spread of globally emerging diseases, and these emerging diseases have proven to be devastating for amphibian populations world-wide. Border and post-border biosecurity activities are pivotal for preventing the introduction of new diseases, but their effectiveness has seldom been assessed. We developed and populated a model to describe transport pathways into Australia, and the biosecurity activities implemented to manage these pathways. We evaluated the capacity of Australian border and post-border biosecurity activities, frequently considered one of the best quarantine inspection services in the world, to prevent the introduction of alien ranaviruses via the unintentional transport of alien amphibians into six Australian States. High transport pressures, measured by the number of international airline passengers and ships arriving in each State, resulted in increasing total numbers of alien stowaway amphibians. Post-border detection of alien amphibians was variable across States and increased with the full-time equivalent employees devoted to post-border biosecurity in each State. The baseline probabilities of introduction, without biosecurity activities, for at least one infected amphibian into any State were very low (≤0.07 in all cases), January 2004-December 2012. The implementation of biosecurity activities reduced these introduction probabilities further, with reductions of up to 50% for some States. Synthesis and applications. We have demonstrated the efficacy of biosecurity activities in reducing the introduction risk of new diseases being transported unintentionally alongside alien amphibians. Critically, we found that not all alien amphibians had to be detected to reduce risks appreciably. We advocate the widespread adoption of border and post-border biosecurity activities to manage the risks posed by alien amphibians (and other stowaway species) as vectors of emergent diseases. We support the robust design of biosecurity activities by providing a framework to evaluate the likely outcomes of case-specific biosecurity arrangements.