Yellow head virus from Thailand and gill-associated virus from Australia are closely related but distinct prawn viruses

Corresponding genomic regions of isolates of yellow head virus (YHV) from T hailand and gill-associated virus (GAV) from Australia were compared by RT- PCR and sequence analysis. PCR primers designed from sequences in the GAV O RF1b polyprotein gene amplified the corresponding 577 nucleotide region of the YHV genome. Comparison of the amplified region indicated 85.1% nucleoti de and 95.8% amino acid sequence identity. YHV PCR primers designed to ampl ify a 135 nucleotide product previously described as a YHV diagnostic probe failed to amplify the corresponding product from GAV RNA. However, the cog nate GAV sequence for this and another recently reported YHV sequence were located in an upstream region of the ORF1b gene. A comparison of these sequ ences indicated identities of 83.0 and 80.9 % at the nucleotide level and 8 6.7 and 86.5 % at the amino acid level, respectively. The data indicate tha t GAV and YHV are closely related but distinct viruses for which differenti al diagnostic probes can be applied.