Updated distribution and characterization of crayfish plague and microsporidiosis affecting Austropotamobius pallipes complex in Trentino (Northeast Italy)

One of the causes of the decline in distribution and abundance of the endangered white-clawed crayfish Austropotamobius pallipes complex throughout Europe is the widespread invasion of alien crayfish and the associated spread of infectious diseases, primarily crayfish plague caused by Aphanomyces astaci. Although this disease usually causes mass mortality in A. pallipes, some wild populations appear tolerant towards A. astaci. Another relevant disease is microsporidiosis (porcelain disease), caused by the parasites Astathelohania contejeani and/or Nosema austropotamobii. In 2021-2024, we conducted a monitoring survey, aimed at mapping the distribution of A. astaci, A. contejeani and N. austropotamobii in wild populations of A. pallipes in Trentino (Northeast Italy). We applied non-invasive sampling methods to collect cuticular swabs from 31 of the 46 known populations, investigate the presence of A. astaci and if possible, identify its genotype through molecular analyses. Aphanomyces astaci was detected in 8 populations, and the presence of a low pathogenic genotype (genotype A) was confirmed in one of them. Thirty-three specimens from 10 populations showed macroscopic signs of porcelain disease, abdominal muscle tissues were collected and subjected to molecular evaluation. The presence of A. contejeani was identified in 23 individuals from 9 populations and N. austropotamobii was detected in 3 individuals, from 3 populations. 8 specimens collected from 6 populations were co-infected by the two microsporidians. This study was partly supported by the EU LIFE Programme: LIFE-CLAW, Crayfish Lineages Conservation in North-western Apennine (LIFE18 NAT/IT/000806), and by the SAGA and SAGA2 collaborative projects between FEM and IZSVe.