NAAHLS Research on Reportable Diseases - Finfish Pathogens

Viral Hemorrhagic Septicaemia Virus (VHSv) occurs throughout the Northern Hemisphere in both fresh and saltwater ecosystems.  DFO’s NAAHLS lab at the Pacific Biological Station in Nanaimo, BC is the National Reference lab for this pathogen. In Canada the virus was initially only detected in the marine and estuarine waters off the East and West Coasts. However in 2005 the virus emerged in the Great Lakes with the first detection occurring in Lake Ontario. Since its first detection, the virus caused significant mortality of over 35 species of freshwater finfish. This virus is a reportable disease in Canada.

Link to OIE: http://www.oie.int/index.php?id=171&L=0&htmfile=chapitre_vhs.htm

NAAHLS Research on Viral Hemorrhagic Septicaemia Virus (VHSv)

Diagnostic Test Development and Validation for Viral Hemorrhagic Septicaemia Virus (VHSv)

In an effort to determine the geographic distribution and prevent the spread of this emerging virus, a surveillance program was set up in the Great Lakes Basin and the upper St. Lawrence River in 2007 by the Canadian Food Inspection Agency and Fisheries and Oceans Canada. To facilitate the surveillance program an accurate and rapid diagnostic test for the detection of VHSv was developed and validated by Dr. Kyle Garver. The test method, a genetics-based test (VHSv quantitative reverse transcription polymerase chain reaction or VHSv RT-qPCR), proved highly sensitive, accurate,bh and enables large numbers of samples to be screened within a few hours.

DFO’s Gulf Biocontainment Unit - Aquatic Animal Health Laboratory (GBU-AAHL) supported the development and validation of the molecular diagnostic test for the VHS virus by providing VHS-infected fish tissues through controlled experimental challenges involving VHS strains in salmon and trout. Experimental challenges are useful for VHS strains not currently recognized in Canada (i.e., exotic strains). GBU-AAHL facility is the only aquatic animal laboratory in Canada that can perform challenge studies with pathogens that are exotic to Canada. These same experimental systems at GBU-AAHL may also be used to assess the susceptibility of various fish species that have not been previously exposed to VHS infection and disease.

Viral Hemorrhagic Septicaemia Surveillance in the Great Lakes

A surveillance program was set up in the Great Lakes Basin and the upper St. Lawrence River in 2007 by the Canadian Food Inspection Agency and Fisheries and Oceans Canada in response to large mortality events that were occurring due to VHSv during that time. This surveillance initiative was implemented in conjunction with the U.S., where a similar VHS surveillance initiative was underway to determine the distribution of the virus in susceptible wild freshwater fish populations in high-risk areas and gain insight into the pathways by which the virus spreads. This bilateral surveillance effort helped build empirical evidence for substantiating ‘freedom from disease’ in key regions in order to support disease control measures and minimize trade disruptions associated with the virus.

To better understand the epidemiology and evolution of this strain of VHS virus, scientists at the Pacific Biological Station and the Gulf Fisheries Centre collaborated from 2005 to 2008 to characterize the genetic diversity of virus strains taken from marine and freshwater environments of North America. The research team assessed the pathogenicity of viral genetic variants and used a genomics approach to better understand the host response to infection, the development of disease, and the recovery from (or resistance to) clinical VHS virus disease.

Investigations of VHSv in other parts of Canada

In addition to causing mortality of finfish in the Great Lakes, VHSv also poses a threat to marine species present in the marine water of British Columbia. In an effort to understand the epidemiology, evolution, and pathogenesis of VHSV strains present in the Canadian aquatic environments, the VHSv reference laboratory at the Pacific Biological Station genetically characterizes each isolate and maintains archival storage in order to monitor changes in virulence and strain variations of new isolations as compared to historical occurrences. Monitoring of VHSv types in the marine waters of British Columbia has revealed that identical virus strains are shared between wild and farmed fish, providing evidence for viral transmission between wild and farmed fish populations. Moreover this work revealed that these virus transmission events, whereby VHSv spilled-over from a wild marine reservoir to a farmed salmon population, were sporadic and did not resulted in a salmon adapted virus strain. Additionally to understand the pathogenesis of various VHSV strains on particular fish species, the Virology program at PBS conducts live virus exposures under controlled laboratory conditions. For instance the PBS Virology research team recently characterized the susceptibility and host response of farmed Atlantic salmon to VHSV strains present in the Pacific Ocean.

For more information: Tracking & characterizing VHS in Canada

Infectious hematopoietic necrosis virus (IHNv) is present in Europe, Japan and along the west coast of North America, ranging from British Columbia (BC) to Alaska, but also extending to the Kamchatka Peninsula. The virus occurs naturally in wild Pacific salmon populations where it rarely causes disease in adult fish but can lead to acute outbreaks in fry and juvenile fish under appropriate conditions. In addition Atlantic salmon are also particularly susceptible to the virus and since the introduction of farming Atlantic salmon in BC and Washington state several outbreaks have occurred in the marine open net-pen farms. DFO’s NAAHLS lab at the Pacific Biological Station (PBS) is recognized as the National Reference Laboratory for IHNv. The IHN virus is a reportable disease in Canada.

Link to OIE: http://www.oie.int/index.php?id=171&L=0&htmfile=chapitre_ihn.htm

NAAHLS Research on Infectious Hematopoietic Necrosis Virus (IHNv)

Utilizing controlled laboratory studies the PBS Virology laboratory has established estimates for the key parameters required in the dispersion of virus and transmission of disease from infected Atlantic salmon aquaculture sites. Coupling the IHNv transmission parameter estimates with physical water circulation models, has provided a tool assess IHNv dispersal and provide accurate geospatial predictions of risk for IHNv transmission from marine salmon sites. Additionally the Virology team at PBS also conduct studies into preventative treatments and vaccination strategies such as the use of APEX-IHN® vaccine to safeguard against this deadly disease and further prevent of the disease.

For more information on NAAHLS research on IHNv:

• Key viral characteristics for Infectious Hematopoietic Necrosis virus (IHNv) in Atlantic Salmon
• Refinement of an Infectious Hematopoietic Necrosis virus dispersion model for the Discovery Islands area and an extension to west coast of Vancouver Island
• New rapid detection technique offers new tools to manage IHNv

Infectious pancreatic necrosis virus occurs in Canada and causes disease in a wide variety of freshwater and saltwater finfish species.  DFO’s NAAHLS lab at the Freshwater Institute (FWI) in Winnipeg, MB is the National Reference Laboratory for this pathogen.  The IPN virus is listed as a reportable disease in Canada.

NAAHLS Research on Infectious Pancreatic Necrosis Virus (IPNv)

Dr. Clouthier at DFO’s Freshwater Institute (FWI) has developed a new IPNv reverse transcription (RT) qPCR assay and validated its performance compared to existing conventional RT-PCR and virus isolation assays. The diagnostic evaluation established test performance parameters, such as repeatability within a laboratory, reproducibility across laboratories, as well as diagnostic specificity and sensitivity. The IPNv RT-qPCR test method is currently used for surveillance, surveys, trade purposes, and research. It also serves as a critical tool in research projects at FWI, such as the one designed to characterize IPNv in Western Arctic Dolly Varden (Salvelinus malma malma), a species that is being considered for listing under the Species at Risk Act.

Infectious Salmon Anaemia Virus (ISAv) can cause mass die-offs in Atlantic salmon populations, but has also been found in other salmonid species. Fish infected with ISAv show signs of liver and spleen inflammation, hemorrhaging, congestion of internal organs and anemia, often leading to death. The virus was initially reported in Norway and later in Canada, the US, Chile, and the United Kingdom.  DFO’s NAAHLS lab at the Gulf Fisheries Centre (GFC) in Moncton, NB is the National Reference Laboratory for this pathogen.  The ISA virus is a reportable disease in Canada.

Link to OIE:  http://www.oie.int/index.php?id=171&L=0&htmfile=chapitre_isav.htm

NAAHLS Research on Infectious Salmon Anaemia Virus (ISAv)

At DFO’s Gulf Fisheries Centre (GFC) lab in Moncton, NB, molecular scientist Nellie Gagné led a team that developed a diagnostic test for ISAv that detects the presence or absence of a particular part of the pathogen’s genetic code in fish or fish samples and validated its effectiveness in collaboration with Dr. Charles Caraguel of the Atlantic Veterinary College in PEI. Validating the new diagnostic test for ISAv ensures that the test accurately measures what it is intended to measure. Results of the validation research — which involved computer modelling and complex statistical analysis comparing this test with other diagnostic tests for ISAv — revealed that this new diagnostic test is more sensitive than other ISAv diagnostic tests making it ideal for screening populations.

The ISA disease dynamic is influenced greatly by field conditions and the rapid mutation of the virus. GFC scientists regularly study the various virus isolates in controlled model challenges. Some ISAv strains cause very low mortalities in Atlantic salmon, whereas other strains can lead to high mortalities or outbreak conditions. A better understanding of the virulence of the various ISAv strains will support the intelligent and cost-effective management of disease outbreaks. The immune response of Atlantic salmon to ISAv was also examined by GFC scientists and an immune response by the salmon was clearly seen when exposed to ISAv. This immunity provides fish with long term protection against ISAv, including the most virulent forms of the virus.

A multi-disciplinary team of scientists from GFC and Novartis is investigating novel approaches for vaccines against ISAv. Some approaches explore the use of recombinant ISA virus protein subunits combined in vivo to fish heat shock proteins. Other approaches aim at injecting a DNA vector expressing a form of vaccine through the fish’s own cell machinery. Complementary research is also ongoing to develop a novel form of vaccine based on the RNA interference mechanism, which works by transfecting fish cells with small RNA molecules that act as guides in targeting and destroying pathogens. These projects help scientists to better understand the immune system of Atlantic salmon and may eventually lead to the development of improved vaccines.

For more information:

• Use of Genomics to Control Infectious Salmon Anemia Virus (ISAv)
• Determining the immune response of Atlantic salmon to infectious salmon anemia virus (ISAv)
• New Brunswick research to characterize strains of ISA in Bay of Fundy
• Researchers identify genetic markers of the immune response to ISA
• Novel recombinant vaccine models against Infectious Salmon Anemia Virus (ISAv)
• How do different strains of ISAv affect fish in the field?
• ISA prevalence and sampling strategy in relation to outbreak stage and vaccination status
• Researchers use DNA chips to uncover immune response to ISAv isolates
• Moncton lab validates assay for the detection of ISA and MSX
• Transcriptional response comparison of naturally immunized ISAv resistant Atlantic Salmon and naïve Atlantic Salmon challenged with a highly virulent ISAv isolate
• DNA vaccine models against infectious salmon anemia virus (ISAv)
• Low pathogenic Infectious Salmon Anemia virus (ISAv) in vivo: a comparative genomic study
• Development of novel RNA-based treatments against ISAv
• DNA vaccine models against ISA

Koi Herpes virus can cause an infectious disease in Common carp (Cyprinus carpio) and Koi carp (Cyprinus carpio koi) and is a reportable disease in Canada. This pathogen has spread to many countries, including Canada, through the trade in Koi carp. DFO’s NAAHLS lab at the Freshwater Institute in Winnipeg, MB is the National Reference Lab for this pathogen.

Link to OIE: http://www.oie.int/index.php?id=171&L=0&htmfile=chapitre_koi_herpesvirus.htm

NAAHLS Research on Koi Herpes Virus (KHv)

Dr. Sharon Clouthier at DFO’s Freshwater Institute (FWI) has conducted a number of studies investigating various aspects of the Koi Herpes Virus (KHv). One project modified an existing qPCR assay designed to detect KHv (also known as CyHV-3) and validated its performance compared to conventional PCR and virus isolation assay. The diagnostic evaluation will establish test performance parameters such as repeatability within a laboratory, reproducibility across laboratories as well as diagnostic specificity and sensitivity. This qPCR test method is currently being used in research projects, such as characterizing KHv in Common carp (Cyprinus carpio) from Lake Manitoba, the location of a KHv disease outbreak in 2008.

Another project looked at how molecular epidemiology can be used to differentiate virus strains and possibly provide insight into viral trafficking patterns that resulted in the introduction of Koi Herpes virus (KHv) (also known as the strain CyHV-3) to the Lake Winnipeg watershed. This project will establish the genotype of the Lake Manitoba virus and assess its phylogenetic relationship to other viruses in the Alloherpesviridae family. Virus load and prevalence as well as the seroprevalence of CyHV-3 antibodies will be assessed in adult carp collected one or two years following a 2008 die-off event associated with KHv in Lake Manitoba. The results of this study may provide further insight into the epidemiology of KHv in wild populations of carp.

Spring Viraemia of Carp virus can cause disease in several freshwater fish species and was detected in Lake Ontario, Canada in 2006. The virus is now widespread in many countries, including Europe, China, Iran, Brazil, and countries of the former Soviet Union.  DFO’s NAAHLS lab in Winnipeg, MB is the National Reference Laboratory for this pathogen.  SVCv is a reportable disease in Canada.

In late June 2006, adult Common carp were collected from Hamilton Harbour, Ontario for export to another country. The carp were spawning at the time and showed no clinical signs of disease. As a condition of export, the carp were held in a land based open facility while undergoing diagnostic testing for pathogens required by the receiving country. Results showed the carp were infected with the Spring Viremia of Carp virus (SVCv). From 30 pooled fish samples, the virus was detected in 18 samples. As a result of the SVCv findings, the shipment was cancelled.

Link to OIE: http://www.oie.int/index.php?id=171&L=0&htmfile=chapitre_svc.htm

White Sturgeon Iridovirus virus was historically suspected to occur in Canada but its presence has not been confirmed.  It is listed as a reportable disease in Canada.

NAAHLS Research on NCLDv

Nucleo-cytoplasmic large DNA viruses (NCLDv) of sturgeon (Acipenseridae), which includes the White Sturgeon Iridovirus (WSIv), were previously recognized as unclassified members of the family Iridoviridae and are now potential members of the Mimiviridae family. The recent description of Namao virus, a new NCLDv in Lake Sturgeon (Acipenser fulvescens) by Dr. Clouthier and colleagues at the DFO’s Freshwater Institute, provides evidence of a new NCLDv lineage comprised of these sturgeon viruses and the phylogenetic relationship to other viruses in the NCLDv clade. Conventional and qPCR assays are being designed to detect sturgeon mimiviruses and assess the distribution and prevalence of the virus in populations of Lake sturgeon in Alberta, Saskatchewan, Manitoba, and Ontario. Ongoing analysis of the virus genome sequence will provide further insight into the evolutionary origin of the virus.

Ceratomyxa shasta is a microscopic multi-cellular parasite that causes a disease in salmon and trout. The parasite is only known to occur along the west coast of North America and requires an invertebrate host to complete its life-cycle. The invertebrate host is a polychaete worm that inhabits river sediments and releases the stage of the parasite that is infective to fish in freshwater. The infection may persist after the salmon migrates to the ocean. The parasite first occurs in intestine of the fish but severe infections can involve several organ systems of the fish. Affected fish may appear darker and have reduced appetite and swimming performance. In severe infections, the belly may appear swollen and the eyes may protrude. All salmonids appear susceptible to infection however the severity of the disease and mortality depends on a number of factors including age and infectious dose. Salmon from rivers in which ceratomyxosis is endemic appear more resistant to the infection than those from rivers without the parasite.  Dr. Simon Jones at the Pacific Biological Station studies strain variation in Ceratomyxa shasta with colleagues in the United States.  Ceratomyxosis is a reportable disease in Canada.