RESUMO
A pathogen of giant freshwater prawn, Macrobrachium rosenbergii, was recently recorded in a hatchery in Yogyakarta. The clinical symptom in post-larvae (PL) was a whitish appearance of the muscles in the tail. Histological examination revealed myonecrosis with massive infiltration of myonuclei and hemocytes. RT-PCR products of 850 bp were obtained when using RNA from diseased PL as a template. The clinical signs and RT-PCR amplicon were reproduced in M. rosenbergii inoculated with bacteria-free inocula. Electron microscopy demonstrated that the M. rosenbergii nodavirus (MrNV) was icosahedral in shape and 28.12 ± 2.31 nm in diameter. RT-PCR products of the RNA-dependent RNA polymerase gene (RNA-1) and capsid protein gene (RNA-2) of MrNV were obtained using designed primer pairs, cloned into pBluescript-KS, and sequenced. The 1312 nucleotide (nt) sequence of MrNV RNA-1 revealed 98.0 % identity with isolates from China and India. Additionally, the 1112 nt sequence of MrNV RNA-2 displayed 98.0 % identity with isolates from China and Taiwan. Disease control efforts involving disinfection of PL, broodstocks, water media, tanks, equipment and ponds successfully eradicated white tail disease from the hatchery. This study is the first report on white tail disease and the isolation and characterization of MrNV in Indonesia.
