In 2012, diseased P. monodon from North-QLD farms were investigated by QDAFF, Townsville. All prawns tested negative using an OIE-endorsed YHV-1 specific PCR test but positive to GAV (YHV-2) and to YHV-1 using OIE-endorsed nested PCR tests designed to co-detect and differentiate YHV-1 from GAV. However, consistent with the YHV-1 specific PCR test data, none of the diseased P. monodon displayed histopathology consistent with acute YHV-1 infection.

Analyses undertaken at CSIRO-AAHL confirmed the presence of GAV but not YHV-1. In two OIE-endorsed PCR tests, GAV sequences were also amplified by primers supposed to be specific for YHV-1. When an OIE-endorsed PCR test designed to detect all YHV genotypes was applied to tissue from healthy P. monodon broodstock imported into QLD from NT, sequence analyses identified an undescribed unique genotype designated tentatively as YHV-7. YHV-7 was also amplified by a CSIRO in-house real-time PCR test designed to be specific to the YHV-1.

Wild QLD broodstock are increasingly being replaced by wild NT broodstock to produce resilient fast growing P. monodon for aquaculture. The finding of YHV-7, with unknown pathogenic potential and distribution, highlights the potential risks of translocated broodstock spreading unwanted new pathogens to regions with substantial aquaculture interest, and supports a need to update decade-old data on what viruses might exist in NT and QLD populations of P. monodon.

Collectively these discoveries highlight urgent needs to (i) re-evaluate genotype specificities of OIE-endorsed PCR tests for different YHV genotypes (ii) redesign PCR tests to improve their power to discriminate YHV-1 from less virulent genotypes and (iii) re-assess the prevalence of GAV and related genotypes (YHV-7) and other endemic viruses potentially problematic to aquaculture (MoV, MBV, HPV, SMV, IHHNV) in wild P. monodon broodstock sourced from the NT and QLD.