Rediscovery of the Australian strain of infectious hypodermal and haematopoietic necrosis virus

In this study we rediscovered and verified the presence of an infectious hypodermal and haematopoietic necrosis virus (IHHNV) strain amongst cultured penaeid prawns Penaeus monodon from 1993 in Australia on the basis of a PCR analysis with IHHNV specific primers and sequencing of the resulting amplicons. A total of 7 previously published diagnostic primers specific to IHHNV were tested against Australian penaeid prawns and only 1 elicited a positive IHHNV PCR result with 16 out of 20 Australian P. monodon samples examined. In comparison, all 7 primers produced IHHNV-positive amplicons from the New Caledonian control samples. Analysis and comparison of the 392 bp fragment derived from the Australian IHHNV strain (AY590120) with other geographical isolates revealed that the Madagascar isolate shared the highest nucleotide similarity (96.2%) and the Hawaiian and New Caledonian strain the highest nucleotide divergence (90.1 and 90.3% respectively). The high nucleotide variation observed between the Australian and Hawaiian strains provides an explanation for the lack of IHHNV detection amongst Australian prawns with published IHHNV PCRs and commercially available gene probes as they are primarily designed on the basis of the Hawaiian strain (AF218266). Results indicated that IHHNV has been present in Australia for a long (geological and contemporary) time and that the virus is endemic in penaeid prawns in the Australian environment.