A case report of interspecies transmission of nervous necrosis virus (NNV) between red seabream brood (Pagrus major) and juvenile Pacific cod (Gadus macrocephalus)

The viral infectious disease called viral nervous necrosis (VNN) or viral encephalopathy and retinopathy (VER) is a particularly lethal virus for larvae and juvenile fish, and seven genotypes have been reported thus far. These viruses are capable of both vertical and horizontal transmission. In this study, molecular biological and histopathological analyses were performed to determine the cause of mass mortality in juvenile Pacific cod (Gadus macrocephalus), which began to feed on red seabream (Pagrus major) eggs. Vacuolization, one of the characteristic symptoms of VNN, was confirmed in the brain and eyes of brood red seabream (P. major) and juvenile Pacific cod (G. macrocephalus). In addition, the inclusion body-like structure was confirmed in the electron microscopic analysis of the gonads and eggs of brood red seabream (P. major). In molecular biological analysis, the target bands were also found in the brain, kidney, liver, spleen, gonad (P. major brood only), and egg (P. major brood only). This vertical/horizontal interspecies transmission needs to be controlled with particular care when producing seedlings, considering that seedlings can be produced for release for the creation or recovery of aquatic resources in addition to aquaculture.