A Rapid Genetic Test for the VHS Fish Virus and Viral Load from Laboratory Challenge Experiments

A unique and emerging strain (IVb) of viral hemorrhagic septicemia virus (VHSv) has outbroke since 2005 in the Great Lakes, killing many important fishes - including muskellunge and yellow perch. The virus poses extensive risks to fisheries, aquaculture, and baitfish industries. Cell culture, which is a weeks (to months)-long laborious process, is the only currently approved VHS diagnostic method. Our new molecular assay, Standardized Reverse Transcriptase Polymerase Chain Reaction (StaRT-PCR) is designed to greatly speed detection time (to hours) and increase accuracy – eliminating false negatives and false positives via a standardized mixture of internal standards (SMIS). We additionally are fine-tuning our test to uniquely identify among VHSv strains and to distinguish whether the virus is actively replicating (transmissible). We here evaluate our StaRT-PCR results on infected fish cell lines and immersion and injection-challenged live fish experiments, in comparison with cell culture, plaque assay, and quantitative Real-Time (qRT)-PCR diagnostic tests. Results to date show that StaRT-PCR is more accurate, with fewer false negatives. We also find that quantities of virus vary widely among experimentally infected individuals, and do not significantly differ between fish showing clinical signs of infection versus those without.