Detection of Macrobrachium rosenbergii Nodavirus (MrNV) of White Tail Disease (WTD) in Apparently Healthy Giant Freshwater Prawn, Macrobrachium rosenbergii in Korea

White tail disease (WTD) is caused by the Macrobrachium rosenbergii nodavirus (MrNV) and an extra-small virus (XSV). MrNV belongs to the Nodaviridae family. While the role of XSV in the pathogenicity of WTD remains unclear, MrNV is considered to be a significant factor in the disease. To study WTD infection in giant freshwater prawns (Macrobrachium rosenbergii), adult and post-larval (PL) prawns were collected from three giant freshwater prawn farms in Gyeongsangnam-do, Korea in 2021. Although the adult and PL prawns did not display any gross signs of WTD, MrNV was detected in both adult and PL in this study. However, XSV was not detected in both prawns. Phylogenetic analysis revealed that the capsid protein gene sequences of MrNV obtained in this study were robustly clustered with the MrNV group, and were clearly distinguished from Alphanodavirus and Betanodavirus groups of the family Nodaviridae. Although Zenker’s necrosis and myolysis were observed histopathologically in the abdominal striated muscle of adult and PL prawns, no gross signs associated with white tail were observed because of local lesions.