Granulomatous dermatitis in turbot (Scophthalmus maximus L.) associated with natural Aeromonas salmonicida subsp salmonicida infection

Furunculosis is a worldwide bacterial disease of salmonids that has also been reported in numerous nonsalmonids fish, such as turbot, Scophthalmus maximus (L.). In this study, gross and histological lesions in farmed turbot naturally infected with Aeromonas salmonicida subsp. salmonicida were described. Sampled fish showed single or multiple cutaneous nodules, always located on the ocular side of the body. On light microscopy these nodular lesions consisted of chronic dermal granulomas that often involved dermal tubercles. The leukocyte population was mainly composed of macrophages, epithelioid cells, giant multinucleate cells and lymphocytes indicating a cellular immune response related with a hypersensibility reaction. The histologic pattern suggested that inflammation began in the deep dermis, and subsequently extended towards superficial dermis, causing detachment of dermal tubercles and ulceration, in severe cases. The bacterial antigen was detected by immunohistochemistry in some granulomas, demonstrating the ability of bacteria to induce a chronic granulomatous response in infected turbot and the possible persistence of the bacteriuminto the granulomas. Since macroscopic and microscopic features of skin nodules observed in turbot differed from the furuncle-like lesions found in salmonids, the use of the term furuncle in turbot will be discussed. (C) 2014 Elsevier B. V. All rights reserved.