eDNA-based crayfish plague monitoring is superior to conventional trap-based assessments in year-round detection probability

The crayfish plague disease agent Aphanomyces astaci is a major threat to European crayfish populations, leading to mass extinctions when spores are transmitted into habitats of native species by infected invasive crayfish species. Current methods for detecting crayfish plague in carrier crayfish populations depend on time-consuming capture of individuals and screening via molecular methods. Highly sensitive environmental DNA (eDNA) methods are a promising tool for rapid and cost-efficient monitoring of pathogens in freshwater systems directly in water samples. For evaluating the usefulness of eDNA for A. astaci detection, the trap-based crayfish plague monitoring followed by qPCR screening of tissue samples was compared to an eDNA-based system to detect A. astaci- spores at a stream inhabited by an infected carrier crayfish population of Pacifastacus leniusculus. The presence of A. astaci was confirmed at all investigated sites with both sample types. Both methods showed comparable A. astaci prevalence, with the eDNA method being applicable across a longer annual time span, including winter, with greater reliability than the conventional method. Given the speed and reliability of the eDNA method for crayfish plague detection, this method might be the best choice for routine monitoring and evaluation of crayfish habitats to hinder the disease spread.