Initial Evidence That Gilthead Seabream (Sparus aurata L.) Is a Host for Lymphocystis Disease Virus Genotype I

SIMPLE SUMMARY: Nodular lesions were observed on the skin and fins of 95% of one and a half million juvenile gilthead seabreams cultured in Egypt, shortly after importation from Europe. We undertook a study to describe the clinical disease course, identify the causative agent, and investigate the origin of the causative agent. Preliminary diagnosis based on gross lesions and postmortem examination suggested lymphocystis disease caused by lymphocystis disease virus, Lymphocystivirus, Iridoviridae. Histopathological and ultrastructural pictures were typical of lymphocystis disease virus infections. Polymerase Chain Reaction followed by sequencing and phylogenetic analysis of the major capsid protein gene demonstrated the presence of lymphocystis disease virus genotype I, originally associated with lymphocystis disease in Northern European countries, with 99.7% and 100% nucleotide and deduced amino acid identity values, respectively. Lymphocystis disease virus genotype I has never been reported in this species or in the region. Regardless of whether it has maintained a previously undetected state of endemicity in Egypt or was introduced through importation or contamination of ship ballast water, the findings of this study add to existing knowledge about the lymphocystis disease’s ecology, and lymphocystis disease virus genotypes and their host range. ABSTRACT: Marine and brackish water aquacultures are rapidly expanding in the Mediterranean basin. In this context, Egypt recently received a shipment of a 1.5 million juvenile gilthead seabream (Sparus aurata L.) from European Mediterranean facility. Within a few weeks of their arrival, 95% of the imported fish developed nodules on their skin and fins that lasted for several months. This study was undertaken to describe the clinical disease course, to identify the causative agent, and to investigate its origin. Preliminary diagnosis based on gross lesions and postmortem examination suggested lymphocystis disease (LCD), caused by the lymphocystis disease virus (LCDV; genus Lymphocystivirus, family Iridoviridae). Histopathological and ultrastructural features were typical of LCDV infections. PCR followed by sequencing and phylogenetic analysis of a 306-bp fragment of the major capsid protein (MCP) gene demonstrated the presence of LCDV genotype I, originally associated with LCD in Northern European countries, with 99.7% and 100% nucleotide and deduced amino acid identity values, respectively. LCDV genotype I has neither been reported in this species nor in the region. Regardless of the source of infection, findings of this study add to existing knowledge about the ecology of LCDV genotype I and its host range.