Development of rt-PCR detection kit for betanodavirus infection in finfish
Betanodavirus is the causative agent of a highly destructive disease Viral Nervous Necrosis (VNN) or Viral Encephalopathy and Retinopathy (VER) in larvae and juveniles of several species of marine and freshwater fin fishes across aquaculture facilities. The virus is non-enveloped, icosahedral in shape with a diameter of approximately 25 to 30 nm and contains two segments (RNA1 and RNA2) of positive sense single-stranded RNA (ssRNA) with the RNA2 segment containing the sequence for the viral coat protein. Disease has been reported from more than 35 fish species from tropical to temperate climates from most continents around the world, including India. Clinical disease is most commonly observed in larval and juvenile finfish with mortality rates of up to 100%, but adult fish surviving infection can become asymptomatic carriers. Molecular epidemiology of VNN in wild habitat revealed almost 15% cases of infection without apparent clinical symptoms. The most common mode of transmission appears to be vertically from sub-clinically infected broodstock to progeny during spawning in hatchery facilities. In order to detect the carrier status of fish, the institute has developed rt-PCR based screening system under a DBT sponsored project. The assay and kit has been validated with clinical as well as subclinical cases of betanodavirus infection in both freshwater and brackishwater environment. A prototype kit has been developed and is ready for commercialization. This kit is the first of its kind indigenously developed in the country. A patent application is under processing.