Investigation of lymphocystis disease in Sparus aurata (sea bream) species grown in Aegean Region with molecular methods

The sea bream (Sparus aurata), a member of the Sparidae family, is naturally found in the Mediterranean region from the British Isles to southern Senegal. Türkiye, Greece and Spain are the main producers, accounting for more than 70% of the sea bream production in the Mediterranean. Lymphocystis disease (LCD) is the most frequently reported viral infection in sea bream farms in the South Atlantic and Mediterranean regions. LCD is a self-limiting disease that causes hypertrophy of fibroblastic cells in the connective tissue of fish and is characterized by the formation of whitish, reddish or gray hypertrophic fibroblastic cell nodules in the dermis and sometimes in the internal organs. These hypertrophic cells, called lymphocysts or lymphocystis cells, are usually seen in the skin and fins, but have also been described in several internal organs (such as stomach, spleen, liver, kidney and heart). In sea bream, LCD-related lesions were observed only on the skin and fins of affected fish and usually disappear after 20-45 days depending on water temperature. In this thesis study, LCVD was investigated by molecular methods on samples showing clinical symptoms and suspected subclinical cases obtained from fish farms in Muğla, Aydın and İzmir provinces where sea bream (Sparus aurata) production is concentrated in Türkiye. A total of 298 samples obtained from 6 aquaculture enterprises in the mentioned 3 provinces in 2 different seasons were delivered to IUC (İstanbul Universit-Cerrahpaşa) Veterinary Faculty, Virology Laboratory in cold chain, and DNA extractions were followed by PCR, sequence analyses and phylogenetic studies. The findings obtained showed that lymphocystis disease is frequently observed in farms in Muğla, Aydın and İzmir provinces where sea bream farming is carried out in our country and that it can cause economic losses. Screening of fish for LCDV by real-time PCR has revealed subclinical infection, particularly in contaminated waters without skin lesions. Conventional PCR has helped to sequence the virus to identify circulating strains of the virus. This will provide input into vaccine preparation and vaccination strategies.