Genetics and Biotechnology Unit, Central Institute of Brackishwater Aquaculture, 75, Santhome high road, R.A.Puram, Chennai-600028, India.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Piscine nodavirus is the causative agent of viral nervous necrosis (VNN) or viral encephalopathy and retinopathy (VER) in fish. More than 30 species of fish from different geographical locations of the world have been reported to be susceptible to the virus. In India, the outbreak of the disease was observed in larvae of Asian sea bass Lates calcarifer which suffered heavy mortalities during hatchery rearing phase. The characteristic lethal feature of this virus resulting in cellular vacuolation and neuronal degradation was observed in the infected tissues of brain and spinal cord by histopathology. Electron microscopy revealed viral particles size of 28 to 30 nm in diameter. The presence of virus was also confirmed by RT-PCR resulting in amplification of 430 bp PCR product using specific primers for RNA2 encoding the coat protein gene of the nodavirus. Immunolocalisation of the virus in ovarian connective tissue associated with the oocytes indicated a probable vertical transmission of this virus in Asian sea bass. Infectivity experiments showed that uninfected larvae become infected with nodavirus when reared with the nodavirus-infected fish. This suggests horizontal transmission in the hatchery environment to be a likely source of VNN infections in Asian sea bass.
