Co-infection by a yeast-like organism in Thelohania-infected white-clawed crayfish Austropotamobius pallipes (complex) from Lombardy (Northern Italy).

In September 2011 an outbreak of the microsporidian parasite Thelohania contejeani (Henneguy, 1892) was reported in a population of Austropotamobius pallipes in Lombardy (Northern Italy). Macroscopically affected white-clawed crayfish collected from Agna creek, tributary of the river Chiese, in the province of Brescia, were analyzed using histological and bio-molecular techniques. Microscopicexamination of the abdominal and cardiac striated muscle fibers revealed microsporidia in several developmental stages with abundance of sporophorous vesicles and free mature spores. PCR and DNA sequencing reffered the parasite to species T. contejeani. Nearly half of the specimens affected by thelohaniasis also harboured a systemic infection by a yeast-like organism. Budding yeast-like cells were observed intracellularly in circulating haemocytes and free in the host haemolymph, particularly evident in the haemal sinuses of the hepatopancreas. These elliptical narrow base budding yeast cells (2,1-2,8 x 3,2-5,7 micron), stained positively with silver and periodic acid-Schiff (PAS) reactions. No hyphae or pseudohyphae were recorded. Yeast proliferation in the haemolymphatic system of crustaceans has been described from the order Isopoda, Amphipoda, Calanoida, Anostraca and Decapoda frequently associated with other pathogens. The co-infection of T. contejeani and yeast-like organisms in A. pallipes has been already described in England (Pixell Goodrich, 1965) and it has been speculated that yeasts could cause death by physically inhibiting haemolymph flow, as it was observed in Gammarus pulex. In the italian episode yeast infection was always associated with thelohaniasis (biased sample) and specimens appeared still viable despite heavy yeast proliferation. Further investigation are needed to identify the yeasts and to assess if they could act as primary pathogens or are mere opportunistic.