Morphopathological features of a severe ulcerative disease outbreak associated with Tenacibaculum maritimum in cultivated sole, Solea senegalensis (L.)

This study describes morphopathologic changes in naturally infected farmed Senegalese sole affected by tenacibaculosis caused by Tenacibaculum maritimum. Macroscopic observation, in addition to light microscopy and scanning electron microscopy, was used to study the lesions. Main lesions were characterized by complete loss of epidermis and dermis, as well as extensive necrosis of muscle layers. Mild-to-moderate inflammatory response with the presence of macrophages was noted around hyaline degenerated muscle cells. Gram-negative filamentous bacteria could be detected only at the dermis. Under scanning electron microscopy, filamentous bacteria located over the scales without epithelium could be observed. These findings together with the isolation and PCR detection of the bacteria in kidney and skin tissues suggest that once the bacteria reach the dermis, probably through eroded epidermis, they are able to proliferate and produce enzymes that are responsible for the damage in the underlying tissues.

Immunohistochemical study on the neuroendocrine system of the digestive tract of turbot, Scophthalmus maximus (L.), infected by Enteromyxum scophthalmi (Myxozoa)

In recent years a new parasite, causing severe losses, has been detected in farmed turbot, Scophthalmus maximus (L.), in Northwestern Spain. Dead fish showed emaciation and cachexia caused by severe necrotizing enteritis, which affected all areas of the digestive tract. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. This study was designed to assess the response of the turbot neuroendocrine system against E. scophthalmi infection. Immunohistochemical tests were applied to sections of the gastrointestinal tract of uninfected and E. scophthalmi-infected turbot, and the presence of cholecystokinin (CCK-8), serotonin (5-HT), substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) were documented. A higher abundance of both endocrine epithelial cells (ECs) and nerve cell bodies and fibres for CCK-8, 5-HT and SP were recorded in the gastrointestinal tract of infected turbot, whereas VIP-like substance decreased. The results indicate that E. scophthalmi infection in turbot induced changes in the neuroendocrine system, which may cause alterations in gut motility, electrolyte and fluid secretion, and vascular and immune functions.

Response of Ig-positive cells to Enteromyxum scophthalmi (Myxozoa) experimental infection in turbot, Scophthalmus maximus (L.): A histopathological and immunohistochemical study

In recent years, a new parasite that causes severe losses has been detected in farmed turbot, Scophthalmus maximus (L.), in Northwestern Spain. Dead fish showed emaciation and cachexia caused by severe necrotizing enteritis that affected all portions of the digestive tract. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. This study was set up to gain insights into the immune response of fish against this parasitic infection. The kinetics of immunoglobulin positive (Ig+) cells in spleen, kidney and intestine from turbot experimentally infected with E. scophthalmi was studied. For evaluating both the progress of infection and the lesions induced by the parasite, we performed histopathological studies and for detecting Ig+ cells in situ we used an indirect immunohistochemical method. In fish exposed to the parasite, the number of Ig+ cells significantly increased in the intestine, the target organ of the parasite, whereas in spleen and kidney, haematopoietic organs where the parasite was not detected, the number of Ig+ cells decreased. Furthermore, the pattern of distribution of Ig+ cells changed in all three organs examined in recipient/infected fish compared with control fish (not exposed to the parasite). The results obtained in this study indicate that the infection by E. scophthalmi in turbot induced an immune response that involved changes in the number and distribution of Ig+ cells.