Viral hemorrhagic septicemia virus (VHSV) was first detected in the Laurentian Great Lakes in 2005 during a mortality event in the Bay of Quinte, Lake Ontario. Subsequent analysis of archived samples determined that the first known isolation of VHSV in the Laurentian Great Lakes was from a muskellunge Esox masquinongy collected in Lake St. Clair in 2003. By the end of 2008, mortality events and viral isolations had occurred in all of the Laurentian Great Lakes except Lake Superior. In 2009, a focused disease surveillance program was designed to determine whether VHSV was also present in Lake Superior. In this survey, 874 fish from 7 sites along the U.S. shoreline of Lake Superior were collected during June 2009. Collections were focused on nearshore species known to be susceptible to VHSV. All fish were dissected individually by using aseptic techniques and were tested for the presence of VHSV genetic material by use of a quantitative reverse transcription (qRT) polymerase chain reaction (PCR) targeting the viral nucleoprotein gene. Seventeen fish from two host species at two different sites tested positive at low levels for VHSV. All attempts to isolate virus in cell culture were unsuccessful. However, the presence of viral RNA was confirmed independently in five fish by using a nested PCR that targeted the glycoprotein (G) gene. Partial G gene sequences obtained from three fish were identical to the corresponding sequence from the original 2003 VHSV isolate (MI03) from muskellunge. These detections represent the earliest evidence for the presence of VHSV in Lake Superior and illustrate the utility of the highly sensitive qRT-PCR assay for disease surveillance in aquatic animals.
Viral hemorrhagic septicemia virus (VHSV) is an important pathogen of cultured and wild fish in marine and freshwater environments. A new genotype, VHSV IVb, was isolated from a fish collected from the Great Lakes in 2003. Since the first isolation, VHSV IVb has been confirmed in 28 species, signaling the early invasion and continued spread of this Office International des Epizooties-reportable agent. For surveillance of this virus in both wild and experimental settings, we have developed a rapid and sensitive one-step quantitative real-time polymerase chain reaction (qRT-PCR) assay that amplifies a 100-base-pair conserved segment from both the genomic negative strand and the mRNA positive strand of the nucleoprotein (N) gene of VHSV IVb. This assay is linear over seven orders of magnitude, with an analytical capability of detecting a single copy of viral RNA and reproducibility at 100 copies. The assay is approximately linear with RNA input from 50 to 1000 ng per assay and works equally well with RNA prepared from a column-based or phenol-chloroform-based method. In wild-caught fish, 97% of the cases were found to be more than three orders of magnitude more sensitive using qRT-PCR than using cell culture. Of the 1,428 fish from the Great Lakes region tested in 2006 and 2007, 24% were positive by qRT-PCR whereas only 5% were positive by cell culture. All of the fish that were positive by cell culture were also positive by qRT-PCR. Importantly, qRT-PCR sensitivity is comparable to that of cell culture detection when comparing VHSV viral RNA levels with viral titer stocks, confirming that the high qRT-PCR signals obtained with diagnostic samples are due to the accumulation of N gene mRNA by transcriptional attenuation. The qRT-PCR assay is particularly valuable for rapid and high-throughput prescreening of fish before confirmatory testing by cell culture or sequencing tissue-derived amplicons and especially in detecting infection in fish that do not show clinical signs of VHS.
Viral hemorrhagic septicemia virus (VHSV) is a rhabdovirus found in fish from oceans of the northern hemisphere and freshwaters of Europe. It has caused extensive losses of cultured and wild fish and has become established in the North American Great Lakes. Large die-offs of wild fish in the Great Lakes due to VHSV have alarmed the public and provoked government attention on the introduction and spread of aquatic animal pathogens in freshwaters. We investigated the relations between VHSV dispersion and shipping and boating activity in the Great Lakes by sampling fish and water at sites that were commercial shipping harbors, recreational boating centers, and open shorelines. Fish and water samples were individually analyzed for VHSV using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and cell culture assays. Of 1,221 fish of 17 species, 55 were VHSV positive with highly varied qRT-PCR titers (1 to 5,950,000 N gene copies). The detections of VHSV in fish and water samples were closely associated and the virus was detected in 21 of 30 sites sampled. The occurrence of VHSV was not related to type of site or shipping related invasion hotspots. Our results indicate that VHSV is widely dispersed in the Great Lakes and is both an enzootic and epizootic pathogen. We demonstrate that pathogen distribution information could be developed quickly and is clearly needed for aquatic ecosystem conservation, management of affected populations, and informed regulation of the worldwide trade of aquatic organisms.
Fibropapillomatosis (FP) of green turtles has a global distribution and causes debilitating tumours of the skin and internal organs in several species of marine turtles. FP is associated with a presently non-cultivable alphaherpesvirus Chelonid fibropapilloma-associated herpesvirus (CFPHV). Our aims were to employ quantitative PCR targeted to pol DNA of CFPHV to determine (i) if DNA sequesters by tumour size and/or cell type, (ii) whether subculturing of cells is a viable strategy for isolating CFPHV and (iii) whether CFPHV can be induced to a lytic growth cycle in vitro using chemical modulators of replication (CMRs), temperature variation or co-cultivation. Additional objectives included determining whether non-tumour and tumour cells behave differently in vitro and confirming the phenotype of cultured cells using cell-type-specific antigens. CFPHV pol DNA was preferentially concentrated in dermal fibroblasts of skin tumours and the amount of viral DNA per cell was independent of tumour size. Copy number of CFPHV pol DNA per cell rapidly decreased with cell doubling of tumour-derived fibroblasts in culture. Attempts to induce viral replication in known CFPHV-DNA-positive cells using temperature or CMR failed. No significant differences were seen in in vitro morphology or growth characteristics of fibroblasts from tumour cells and paired normal skin, nor from CFPHV pol-DNA-positive intestinal tumour cells. Tumour cells were confirmed as fibroblasts or keratinocytes by positive staining with anti-vimentin and anti-pancytokeratin antibodies, respectively. CFPHV continues to be refractory to in vitro cultivation.
Leiomyosarcoma with associated retrovirus were found in North America for the first time in adult Atlantic salmon (Salmo salar) held in a quarantine facility at the North Attleboro National Fish Hatchery (NANFH), Massachusetts, USA. The fish had been collected as age 1-2 yr animals from the Pleasant River, Maine, and were to be used as brood stock in a population augmentation program for that river. Neoplastic disease was observed at NANFH initially in older (age 4 yr) fish, followed by age 3 yr fish. Disease was not observed in age 2 yr fish. The mortality pattern was chronic.
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