Isolation and Identification of a New Strain of Nervous Necrosis Virus from the Big-belly Seahorse Hippocampus Abdominalis in China

Abstract

Background: Betanodaviruses , members of the Nodaviridae family, are the causative agents of viral nervous necrosis (VNN) in fish, resulting in great economic losses worldwide. Methods: In this study, we isolated a virus strain named seahorse nervous necrosis virus (SHNNV) from cultured big-belly seahorses Hippocampus abdominalis in Xiamen city, Fujian Province, China. Cell isolation, PCR detection, phylogenetic analysis, qRT-PCR, fluorescence in situ hybridization (FISH) and histology were used for virus identification and analysis of virus histopathology. Furthermore, an artificial infection experiment was conducted for virulence testing. Results: Brain and eye tissue homogenates of diseased big-belly seahorses were inoculated onto a grouper spleen (GS) cell monolayer at 28°C. Tissue homogenates induced obvious cytopathic effects in GS cells. PCR and sequencing analyses revealed that the virus belonged to Betanodavirus and shared high sequence identity with red-spotted grouper nervous necrosis virus (RGNNV) isolates. qRT-PCR and fluorescence in situ hybridization revealed that SHNNV mainly attacked the brain and eye. Histopathological examination revealed that the virus led to cytoplasmic vacuolation in the brain and retinal tissues. Infection experiments confirmed that SHNNV was highly infectious, causing massive death in big-belly seahorses. Conclusion: A novel seahorse betanodavirus from the big-belly seahorse in China was discovered. This finding will contribute to the development of efficient strategies for disease management in aquaculture.