Although Bsal was first described from infections of Fire Salamanders in Europe, from the outset an Asian origin of the pathogen was implicated (Martel et al. 2013). Additional support has been forthcoming that Bsal evolved in Asia, where lethal infections have not been found suggesting that a long co-evolutionary history has led to resistance or tolerance by amphibian species in Asia (Laking et al. 2017). In Europe, infections were first observed in the Netherlands (Spitzen-van der Sluijs 2016), followed by its discovery in Belgium and Germany, and most recently in Spain (Martel et al. 2020). The lethal effect of Bsal on some European amphibian species suggests a recent arrival of a pathogen that encounters naïve hosts. The likely routes of within-continent spread are dispersal of infected amphibians among populations and possibly movement of spores by waterfowl, and by spillover of infected individuals once held in captivity (Nguyen et al. 2017; Yuan et al. 2018). Spread of Bsal between continents including the emergence of Bsal in Europe is likely due to importation of infected species from locations where Bsal in endemic (Nguyen et al. 2017). Anurans from Asia infected with Bsal have been found in a pet store in Germany (Nguyen et al. 2017; Yuan et al. 2018). In addition, Bsal was found on salamander species in China that are frequently imported. These studies suggest a role of trade markets in the between-continent spread of Bsal. In particular, the discovery that anurans can be infected opens up the possibility that trade in frogs for food, research, and pets can lead to between-continent dispersal. Clean Trade measures such as development of Bsal testing and certification procedures that traded animals and fomites in imports to North America are Bsal-free are likely the most effective proactive measure to forestall Bsal emergence in North American (Grant et al. 2017).
The Clean Trade Working Group is assembling in 2020, and development of its scope, including its implementation goals and priorities, are under development at this time. The goal of this group is to engage pet industry stakeholders and expand efforts to forestall potential human-mediated transmission of Bsal into North America via trade markets.