Achieving the mandated dose rate of 50 kGy for prawns harvested from the White Spot Disease control zone in SE QLD is proving to be problematic and industry are requesting a reduction in the permitted irradiation dose rate for prawns sourced from Moreton Bay to somewhere between 15 and 25 kGy. A reduction in treatment dose, if successful, would provide a viable option for industry to continue trade in uncooked prawns sourced from Moreton Bay.
There appears to be only three scientific papers relevant to the subject of using gamma irradiation for inactivation of WSSV (Heidareh et al. 2014, Kakoolaki et al. 2015, Motamedi-Sedeh et al. 2017). The studies were conducted with the aim of determining the doses required to inactivate the Iranian isolate of WSSV with gamma irradiation for the purposes of vaccinating cultured prawns. While the listed scientific papers suggest gamma irradiation at a dose of around 13-15 kGy is effective at inactivating WSSV, their experimental protocols and results are not clearly transferable. In these studies aliquots of free virus were exposed to different gamma irradiation doses. Irradiation of WSSV inside infected host tissues was not performed, and data on whether the surviving prawns were infected with WSSV were not presented. None of these papers are therefore directly applicable to the situation relating to irradiation treatment of WSSV in-situ inside infected prawns.
Given the absence of information on irradiation doses for inactivation of WSSV in the Department of Agriculture (2014) review document, and the absence of research in Australia or overseas to validate alternative irradiation doses that completely inactivate WSSV, new research is urgently required to determine the minimum safe irradiation dose for inactivation of WSSV in prawns with the results verified by controlled challenge trials in a bio-secure facility.