Mass mortality associated with Carpione Rhabdovirus in golden pompano (Trachinotus ovatus) in China: First report

Abstract

A severe epizootic outbreak occurred in a deep-water cultured golden pompano (Trachinotus ovatus) in Guangdong Province, China (August-November 2023); the cumulative mortality was 65-82%. The diseased fish showed clinical signs of lethargy, anorexia, whirling movements, and hemorrhage at the base of the fins and in the upper and lower jaws before mass mortality. A Rhabdovirus strain, CARPV2023, was successfully isolated using FHM cells. Cytopathic effects of the tissue filtrate of the diseased golden pompano on FHM and EPC cell monolayers were characterized by rounded cells, grape-like cluster formation, detachment, and lysis. Histopathology revealed congestion, hemorrhage, and necrosis in the spleen, liver, kidney, and intestinal tissues of naturally and experimentally infected golden pompanos. Electron microscopy showed that bullet-shaped viral particles 183.5-201.6-nm long and 57.3-82.7-nm wide budded from cell membrane or aggregated around the infected FHM cells. The virus remained stable for 7 days at 4-33{degrees}C and grew optimally at 28{degrees}C. Whole-genome sequencing and phylogenetic analysis based on the full genome further indicated that the CARPV2023 strain is a member of Carpione Rhabdovirus, which is related to Novirhabdovirus with unclassification. A specific nested reverse transcriptase-polymerase chain reaction confirmed the presence of CARPV in the affected golden pompano. Much higher mortality was observed in challenged golden pompanos than in the controls through intraperitoneal injection and immersion infection. In situ hybridization showed positive reactions in the fish tissues. This is the first study to report natural CARPV infections in marine fish in the world.