A user's inter-laboratory comparison of broodfish screening for infectious pancreatic necrosis virus using molecular and conventional diagnostic methods.
Individual testing and subsequent removal of eggs from infectious pancreatic necrosis virus (IPNV)-positive parents is required for export of salmonid eggs to some farming countries. Testing by cell culture requires more than three weeks before the eggs can be released from quarantine and incurs significant logistic problems and costs. The feasibility of the RT-PCR testing method as offered by several laboratories was therefore evaluated during the current inter-laboratory comparison study. Frozen kidney sub-samples from 100 motherfish of Atlantic salmon (Salmo salar L.) were shipped to three diagnostic laboratories (A, B and C) for testing by RT-PCR and cell culture. Of the 100 examined samples, all proved IPNV-negative by cell culture. Thirty samples were positive by RT-PCR analyses, but only four of these samples were RT-PCR positive in two laboratories and none in any of the three laboratories. From a disease management point of view, the RT-PCR test outcomes gave no reasonable guidance as to which fish were truly infected and which batches of fertilised eggs should be discarded. This is clearly an unacceptable situation and calls for new research to standardise sample conservation, RNA extraction procedures and amplification techniques, to estimate method sensitivity and specificity, and to validate the method's performance and robustness to support disease control measures in salmonid aquaculture.