Survey on the thelohaniasis in white-clawed crayfish Austropotamobius pallipes complex from streams of Belluno province (Northeastern Italy).

The freshwater crayfish, Austropotamobius pallipes complex is a protected European native species, as it is considered an endangered aquatic organism. From 2004 to 2006, during summer and early autumn, samplings of wild white-clawed crayfish Austropotamobius pallipes complex were carried out for pathological surveys in six streams and rivers of Belluno Province in Veneto region of Northeastern Italy: Gresal, Morol, delle Tose Lake (Lagole), Valturcana, Ardo and Vena d’oro. The samples were collected in order to detect the microsporidian parasite Thelohania contejeani Henneguy, responsible for porcelain disease or thelohaniasis. A total of 177 crayfish was captured, and in particular: 16 in Gresal, 1 in Morol, 20 in delle Tose Lake (Lagole), 90 in Valturcana, 27 in Ardo and 23 in Vena d’oro watercourses. Gross examination of each specimen was performed and only a small number of subjects, in relation to the population consistency, was sacrificed to evaluate the health status. The number of subjects was judged to be the minimum needed for an accurate survey picture, avoiding an excessive wild crayfish collection. Parasitological surveys were performed by microscopical exam of skeletal muscles; histopathological analysis was carried out on full transverse and sagittal sections of cephalothorax and abdomen. The presence of Thelohania contejeani was recorded only in the Vena d’oro crayfish population with a low rate of infection (4.3%). All the subjects sampled from the other watercourses resulted negative. The examination of skeletal muscle from the positive subject revealed the presence of several stages of the microsporidian parasite, with mature spores as the most common stage. Sporophorous vescicles were also present. The mature spores were oval, with a mean length of 4 µm and a mean width of 2.2 µm. At the histological examination the skeletal, cardiac and intestinal muscles showed the fibers heavily filled with spores. Melanine infiltrations were focally present in infected striated muscles. The phagocytotic nephrocytes of the gills were engulfed with small masses of spores. This survey permitted to report for the first time the sporadic presence of T. contejeani in white-clawed crayfish populations from Northeastern Italy, with heavy tissue damages referable to the infection.