Development and validation of a reverse transcription quantitative PCR for universal detection of viral hemorrhagic septicemia virus.

Viral hemorrhagic septicemia virus (VHSV) infects over 70 fish species inhabiting marine, brackish or freshwater environments throughout the Northern Hemisphere. Over its geographic range, 4 VHSV genotypes and multiple subtypes exist. Here, we describe the development and validation of a rapid, sensitive and specific real-time reverse transcription quantitative PCR assay (RT-qPCR) that amplifies sequence from representative isolates of all VHSV genotypes (I, II, III and IV). The pan-specific VHSV RT-qPCR assay reliably detects 100 copies of VHSV nucleoprotein RNA without cross-reacting with infectious hematopoietic necrosis virus, spring viremia of carp virus or aquatic birnavirus. Test performance characteristics evaluated on experimentally infected Atlantic salmon Salmo salar L. revealed a diagnostic sensitivity (DSe) > or = 93% and specificity (DSp) = 100%. The repeatability and reproducibility of the procedure was exceptionally high, with 93% agreement among test results within and between 2 laboratories. Furthermore, proficiency testing demonstrated the VHSV RT-qPCR assay to be easily transferred to and performed by a total of 9 technicians representing 4 laboratories in 2 countries. The assay performed equivalent to the traditional detection method of virus isolation via cell culture with the advantage of faster turnaround times and high throughput capacity, further suggesting the suitability of the use of this VHSV RT-qPCR in a diagnostic setting.