Occurrence of actinosporean stages (Myxozoa) in the Nera River system (Umbria, central Italy).

We investigate the oligochaetes populations in the Nera River systems (central Italy) in order to highlight the occurrence of actinosporean stages in this natural environment. The survey was carried out during 2 years of monitoring 24 stations upstream and downstream the 12 trout farm along the rivers. In four of the 24 sites, oligochaetes releasing Echinactinomyxon and Aurantiactinomyxon types spore were collected. The actinospores observed were described morphologically, by transmission electron microscopy and by molecular analysis. Histological observations of the infected oligochaetes were carried out. A single morphotype of the collective group Echinactinomyxon were detected showing the presence of branches at the distal end of the caudal processes. The morphological and morphometrical characters showed that the Echinactinomyxon type herein described is a novel phenotype. This data has to be confirmed by the molecular comparison with sequences not yet available in GenBank. The molecular analysis of the Aurantiactinomyxon type, showed high genetic similarity (99.8%) with the two alternate stages of Chloromyxum truttae even if our type showed some differences in morphology stressing the importance of combining the two methods to avoid misidentifications. This is the first survey carried out in natural environment in Italy. Further analyses on fish population are required in order to detect myxosporean stage in the vertebrate hosts and confirm the molecular data.