WINTER DISEASE IN ASSOCIATION WITH INTESTINAL NON-FORMING XENOMA MICROSPORIDIA IN GILTHEAD SEABREAM (SPARUS AURATA)

AIM OF THE STUDY: Winter disease (WD) is a multifactorial disease found primarily in sea caged gilthead sea bream (Sparus aurata) along the Mediterranean coast.1,2 An emaciative syndrome has been recently observed in Spain and Enterospora nucleophila, a new microsporidian species of the family Enterocytozoonidae has been described; these intracellular, non-forming xenoma microsporidia, opportunistic in nature exploit a w eakened host immune status, as it could happen in WD.6 Teleost intestine contains Mast Cells (MCs), w hose functional properties are similar to those of mammalian mast cells;5 recruitment of MCs to sites of persistent inflammation is a general response in parasites-affected fish. An increased number of the MCs is also reported in WD-affected fish.3,4 In December 2013 a disease outbreak in sea caged gilthead seabream in Italy, affecting 0+ year fish occurred. The aim of this study w as to evaluate the histopathological changes related to these tw o conditions, to characterize the MCs by immunohistochemistry and the microsporidia by PCR. MATERIAL AND METHODS: From tw enty gilthead sea bream intestinal tracts w ere fixed in buffered formalin at the sample site and sent to DIMEVET. Routine histological sections w ere obtained; Luna stain w as also performed. Immunohistochemistry w ith CD117 antibody (1:100, Dako) w as also carried out. Intestinal tissue w as also subjected to molecular analysis; a fragment of the 18S rDNA w as amplified and then sequenced. RESULTS: Hindgut show ed a moderate dilatation of the lumen in association w ith w hitish casts, similar to the milk-like mucous casts reported in WD outbreaks.1,2 A severe mucosal atrophy w ith total folds flattening w as present; w ithin lamina propria and submucosa a mild to moderate MCs hyperplasia and mild mucous cells hyperplasia w ere observed. Multifocally, w ithin enterocytes and rodlet cells, the nucleus and/or cytoplasm contained microsporidian spores, more evident w ith Luna stain. The sequences obtained from intestines show ed 99.9% identity w ith E. nucleophila. Within perivisceral exocrine pancreatic acini, focal necrosis and MCs infiltration have been observed, as reported by other authors during WD outbreaks. CONCLUSIONS: MCs are interpreted as ‘‘standing force’’ in particular tissues consistently exposed to pathogens, in contrast to a ‘‘mobilization force’’ that has been an advantage in those being exposed to noxious agents only occasionally.7 The severe mucosal flattening could be interpreted as an effect of a chronic insult, not only related to the microsporidia infection; other concurrent predisposing factors as those reported in WD could be then considered into the development of an overt pathology. BIBLIOGRAPHY: 1Birincioglu et al, 2013; 2Colorni, 2011; 3Contessi et al,2006; 4Ibarz et al, 2010; 5Lauriano et al.,2012;6 Palenzuela et al.,2014; 7Reite and Evensen,2006.