In recent years, characterisation of IHHNV isolates from across the Indian and Pacific oceans have revealed a family of RNA viruses with as much as 14% sequence difference between isolates. A new set of PCR primers was developed, and with these primers, archived samples of teh Australian virus tested positive. Subsequent sequencing of the PCR fragment revealed that the Australian virus was indeed IHHNV and was most closely related to isolates from Madagascar that are reported to be avirulent.
In late 2003, individual tiger prawns (Penaeus monodon) caught off the Northern Territory, broodstock originating from Queensland used in a research program, and prawns bred from these broodstock, yielded positive PCR results when tested with the new primer sets. In early 2004, individual wild-caught, adult kuruma prawns (P. japonicus) originating from Queensland also tested positive to IHHNV with the new primer set, and sequence analysis showed an identical nucleotide sequence to the 2003 isolate from P. monodon. None of these prawns had clinical signs of IHHN or histological lesions indicating IHHNV infection, and none reacted with the OIE-recommended PCR test.