A sampling of results and impacts from completed New York Sea Grant-funded research projects, written during the period February 1, 2009 – January 31, 2010
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Freshwater Adaptation and Early Invasion of Viral Hemorrhagic Septicemia Virus into the Great Lakes Basin
R/FTD-10, Bowser / Casey / Farrell / Getchell
This project developed a quantitative Reverse Transcriptase Polymerase Chain Reaction (qRTPCR) assay to detect both the genomic viral RNA (free virus) and viral replicative intermediates (infected cell viral mRNAs) of the Great Lakes isolates of VHSV.
Preliminary testing of the qRT-PCR assay indicates that the test is capable of detection of viral copy number at approximately 10,000 times fewer copies compared to the standard methodologies.
Viral Hemorrhagic Septicemia Virus (VHSV genotype IVb) viral load among smallmouth bass (Micropterus dolomieu) in the St. Lawrence River and the distribution and abundance of VHSV IVb through an annual cycle was assessed using this assay. The viral load across demographic groups (sex and maturity) of fish was also determined. Strong temporal variation in viral prevalence was evident through the annual cycle, with peaks corresponding to the smallmouth bass spawning period and a water temperature range of 10-14°C.
Viral prevalence was markedly higher among sub-adult fish. Given the fact that VHSV IVb is present in fish in the greatest numbers during the spring, monitoring resources should be focused on spring spawning periods, when water temperature is within the aforementioned range.
The development of the qRT-PCR has provided the fish health community with a disease diagnostic and research tool that is far more sensitive than the currently practiced cell culture techniques. The qRT-PCR may serve as a rapid and sensitive initial negative screen of surveillance and fish health inspection samples. By doing this initial screening, a great deal of time and effort will be eliminated from surveillance and inspections of fish populations for the presence of VHSV IVb. It should be noted that the qRT-PCR must be validated to the satisfaction of such bodies as the OIE and the Fish Health Section/American Fisheries Society Blue Book Committee.