Molecular Surveillance Detects Betanodavirus Infection in Farmed and Wild Fishes of India

Abstract

The disease, viral nervous necrosis caused by betanodaviruses is an emerging threat to the fish farming industry. The virus has a broad range of fish hosts and infects all age groups of fishes causing huge economic loss to the entrepreneurs. Acute and latent infections were described for this virus which may also remain dormant/persistent in carrier fishes/invertebrates. Estimation of the prevalence of the virus was attempted in this study using advanced molecular tools. A nested rt-PCR method followed by nucleotide sequencing and subsequent bioinformatics analysis was adopted. Samples were collected from hatchery, marine, coastal & low-saline farms and wild environments from eight sites along the east and west coasts of India. Samples included apparently healthy fishes along with moribund with clinical signs. Nodavirus infection was diagnosed in 19.7% of samples analysed. Prevalence ranged from 40.6% in marine farms, 29.5% in coastal farms, 23.6% in wild marine and 5.6% in wild coastal environments with no infection in the marine hatchery and low-saline farm samples. All the isolates belonged to RGNNV genotype which has the widest host range among all the species of Betanodavirus. This study also identified new susceptible fish species to betanodavirus infection naturally.