Long-term changes in the prevalence of the crayfish plague pathogen and its genotyping in invasive crayfish species in Czechia

The widespread presence of North American alien crayfish in Europe is a major driver of native crayfish population declines, mainly because they are chronic carriers of the oomycete Aphanomyces astaci respon-sible for crayfish plague. Screening for the crayfish plague pathogen in host populations has become a common practice across Europe, but sampling usually covers spatial but not temporal variation. Our study focuses on the current situation in Czechia, where screening forA. astaci was first conducted in the mid-2000s. We provide data about the distribution and prevalence of this pathogen at almost 50 sites with three host crayfish: the spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, and marbled crayfish Procambarus virginalis. Among these sites were 20 localities that were resampled several years (usually more than a decade) after the original screening forA. astaci. We did not detect anyA. astaci infection in two studied P. virginalis populations but documented several new hotspots of highly infected P. leniusculus in Czechia, and the first site with the coexistence of the latter with F. limosus. Our data sug-gest that despite some fluctuations, A. astaci prevalence in North American host populations generally does not tend to change significantly over time; we only observed two cases of a significant increase and one of a significant decrease. We no longer detected A. astaci in several originally weakly infected popula-tions, but our data suggest it likely still persists in these areas and threatens native crayfish populations. At the single known site in the country where P. leniusculus and F. limosus coexist, we documented the presence of the same A. astaci genotype group in both crayfish species, likely due to interspecific transmis-sion of the pathogen from the former host to the latter. However, genotyping of A. astaci in infected host individuals still supported the link between specific pathogen genotypes and crayfish hosts, suggesting that assessment of sources of mass mortalities from the pathogen genotyping is feasible in European regions where the mutual contact of different American crayfish species is uncommon.