Viral encephalopathy and retinopathy

Viral nervous necrosis (VNN), also referred to as viral encephalopathy and retinopathy (VER), has been reported in at least 120 cultured or wild marine and freshwater fish species and has caused serious economic losses among farmed marine fish species in the past decades. Since the first description of this disease at the end of the 1980s, substantial amounts of researches have been instrumental in understanding the mechanisms involved in fish infection, development of reliable diagnostic methods, and disease prevention and control. This chapter presents some important aspects of the disease with particular emphasis on etiologic agent, clinical signs and gross pathology of the disease, histopathology, disease risk factors, virus propagation and identification, molecular diagnostics, and concomitant prevention and control methods