Thelohaniasis in white-clawed crayfish Austropotamobius pallipes complex from Belluno province (North Eastern Italy).

From 2004 to 2006, during summer and early autumn, a parasitological survey aimed at detecting the microsporidian parasite Thelohania contejeani Henneguy, responsible for Porcelain Disease or Thelohaniasis, was performed on 177 wild white-clawed crayfish Austropotamobius pallipes complex captured in six streams and rivers, 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. Parasitological surveys were performed by microscopical exam of skeletal muscles; histopathological analysis was carried out by different histochemical stains on full transverse and sagittal sections of cephalothorax and abdomen. Transmission electron microscopy (TEM) observations have been also conducted on the parasites recovered during the survey. The presence of Thelohania contejeani (Microsporidia, Thelohaniidae) was recorded only in one crayfish from the Vena d’oro population. The examination of skeletal muscle from the positive subject revealed the presence of several developmental stages of the parasite, with mature spores as the most common stage. Sporophorous vescicles were also present. 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 gill phagocytotic nephrocytes 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.