A new ranavirus of the Santee-Cooper group invades largemouth bass (Micropterus salmoides) culture in southwest China

An ulcerative disease of largemouth bass has severely damaged Chinese largemouth bass industry for years. Here, we investigated prevalence of this disease in southwest China and typical cases from 2016 to 2018 were presented. All diseased fish behaved lethargic and inappetent; skin and muscles were severe hemorrhage, ulceration and inflammation; liver, spleen and kidney were necrosis. All cases were proved to relate to the ranavirus infection by PCR detection and pathogen isolation. We observed plenty of hexagonal particles in effected epithelioma papulosum cyprinid. Experimental trials convinced that LMBV-like was the causative agent. Phylogenetic analysis bases on major capsid gene exhibited the distinction between Asian and Euramerica isolates. Further sequence analysis revealed 16 nucleotides mutant which lead to 3 amino acid changes of all Asian strains. In summary, the identification of the pathogen of largemouth bass ulcerative disease in southwest China is essential for the detection and vaccine development, which is vital important for this disease control.