Light and electron microscopic studies on turbot Psetta maxima infected with Enteromyxum scophthalmi: histopathology of turbot enteromyxosis

Abstract

In the last decade, a new parasite that causes severe losses has been detected in farmed turbot Psetta maxima (L.), in north-western Spain. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. The aim of this study was to characterize the main histological changes that occur in E. scophthalmi-infected turbot. The parasite provoked catarrhal enteritis, and the intensity of the lesions was correlated with the progression of the infection and with the development of the parasite. Infected fish were classified into 3 groups, according to the lesional degree they showed (slight, moderate and severe infections). In fish with slight infections, early parasitic stages were observed populating the epithelial lining of the digestive tract, without eliciting an evident host response. As the disease progressed, catarrhal enteritis was observed, the digestive epithelium showed a typical scalloped shape and the number of both goblet and rodlet cells was increased. Fish with severe infections suffered desquamation of the epithelium, with the subsequent release of parasitic forms to the lumen. The dislodged enterocytes underwent anoikis, a mode of apoptosis triggered by the loss of anchorage, which might facilitate spreading of the parasite. Lymphohaematopoietic depletion was also observed, mainly in head kidney and spleen, which could contribute to the high virulence of this parasite.

Novel horizontal transmission route for Enteromyxum leei (Myxozoa) by anal intubation of gilthead sea bream Sparus aurata

“…The disruption of the integrity of the mucosa, desquamation and detachment of the epithelium, which correspond to advanced, chronic infections, was observed earlier than in cohabitation and effluent transmission trials. The apparent decrease in goblet and rodlet cells has also been reported in turbot Psetta maxima with severe E. scophthalmi infections (Bermúdez et al 2010). …”

Effects of Enteromyxum scophthalmi experimental infection on the neuroendocrine system of turbot, Scophthalmus maximus (L.)

“…The presence of the parasite was noteworthy in the pyloric caeca and anterior intestine, preferential sites of E. scophthalmi invasion, from where it extends to the rest of the digestive tract [5]. The association between the presence of the myxosporean in the epithelium of the gastrointestinal tract and epithelial desquamation and inflammatory infiltrates in the intestinal lamina propriasubmucosa concurs with other descriptions of the disease [3,4,9]. In general, the extension and the severity of the lesions were in accordance with the parasite burden.…”

Quantitative and qualitative evaluation of iNOS expression in turbot (Psetta maxima) infected with Enteromyxum scophthalmi

“…In the last stages of the turbot enteromyxosis, the lining epithelium tends to completely detach [34] and there is an increase in the number of enterocytes undergoing apoptosis (authors' unpublished results). One of the main mechanisms of the NOmediated cytotoxicity is the hinder of cellular adhesion events [35].…”