Viral nervous necrosis (VNN) an emerging disease caused by Nodaviridae in aquatic hosts: Diagnosis, control and prevention: A review

Betanodavirus is one of the two genera making up the family Nodaviridae and is the etiological agent of viral nervous necrosis (VNN, also known as viral encephalopathy and retinopathy or VER). The virus infects a large range of host species in more than 50 species of marine and freshwater fish worldwide from different geographical areas and the known host range continues to expand as new species of fish are used for aquaculture. The disease is characterized by vacuolating necrosis of neural cells of the brain, retina and spinal cord and causes up to 100% mortality in larval and juvenile fish, and can cause significant losses in older fish. The lack of knowledge about control and prevention of the disease makes the problem serious and impedes development of management approaches. Therefore this review focuses on current knowledge and future perspectives of viral nervous necrosis in the aquaculture industry with special focus on the type of diagnosis, control and prevention of the disease.