Fisheries and Oceans Canada Develops a Faster Testing Method for Infectious Salmon Anemia Virus

At the Gulf Fisheries Centre in Moncton, New Brunswick, Fisheries and Oceans Canada (DFO) research scientist Dr. Mark Laflamme and his research team have developed a faster way to detect Infectious Salmon Anemia virus (ISAv) by combining the best characteristics of two different diagnostic testing techniques. DFO’s Centre for Aquatic Animal Health Research and Diagnostics funded the development of the new testing procedure in support of the National Aquatic Animal Health Program.

The detection and management of infectious aquatic animal diseases such as ISAv is integral to protecting Canada’s reputation for high-quality fish and seafood, which depends on the ability to deliver accurate, reliable, and consistent diagnostic test results. Responsibility for this testing falls to three of the four laboratories in the DFO National Aquatic Animal Health Laboratory System, where DFO scientists also conduct targeted research and provide scientific advice in support of the National Aquatic Animal Health Program (co-delivered by the Canadian Food Inspection Agency).

Infectious Salmon Anemia virus

The abdomen of an Atlantic Salmon (above) shows skin haemorrhages typical of a fish infected by Infectious Salmon Anemia virus (ISAv). Fisheries and Oceans Canada researchers at the Gulf Fisheries Centre have developed a faster way to detect the virus by combining the best characteristics of two different diagnostic testing techniques.

Photo: Fisheries and Oceans Canada

The photo above shows pinpoint haemorrhages of the skeletal muscle in an Atlantic Salmon collected from a population infected by Infectious Salmon Anemia virus. The new diagnostic screening method for ISAv enables the live virus to be identified an average of 25 days faster than with the traditional virus isolation protocol alone.

Photo: Fisheries and Oceans Canada

According to the Canadian Food Inspection Agency (CFIA), ISAv outbreaks are most common in susceptible farmed finfish reared in sea water. Depending on the virus strain, the disease can potentially kill up to 90 per cent of an infected Atlantic Salmon population, representing significant economic losses for aquaculture operations. However, the average death rate at any given farm is about 30 percent. Rainbow and Brown Trout are also susceptible to ISAv. The CFIA indicates there is no evidence that the virus can be transmitted to humans.

ISAv is a reportable disease in Canada, which means anyone who owns or works with aquatic animals and knows of, or suspects, a case of ISAv is required by law to notify the CFIA. To date, there have been confirmed reports of the disease in New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland and Labrador. A surveillance program for the disease in the coastal waters of British Columbia and its watershed was initiated by CFIA in 2012. No cases of ISAv have been confirmed there to date.

Improving diagnostic testing

Confirmatory testing for ISAv has traditionally used a virology approach, which involves growing the virus from a tissue sample and then examining it under a microscope.

“If enough of the virus grows, we can actually see the virus killing the cells. However, one of the drawbacks of this type of test is it can take considerable time to get the results—up to 40 days depending on how infectious the original virus was,” says Laflamme. “The goal of our research was to find a way to make ISAv testing faster. The new testing protocol will enable us to get results to clients up to 25 days sooner than with the traditional method, which is important for the aquaculture industry since test results may influence when they want to harvest, for example.”

A more rapid approach involves a molecular biology method called quantitative polymerase chain reaction (qPCR). In forensic science, PCR techniques can be used as a tool for genetic fingerprinting in which DNA samples are analyzed to identify an individual’s unique genetic code. In animal health research, qPCR is a very rapid and sensitive testing method that can be used to detect the genetic material of a target organism— such as a pathogen (disease-causing agent)—as well as an indication of the amount of pathogen present.

“The disadvantage of qPCR is it detects all of the virus, both dead and alive. For that reason, many lab clients prefer the standard virology method as it provides more accurate and critical information about the amount of live virus present,” says Laflamme.

The new ISAv testing protocol approach blends the best characteristics of both types of testing by using a qPCR test first to assess the amount of virus present in a sample, and a standard virology test to grow the virus for 9 to 14 days. A second qPCR test is then carried out to assess the amount of live virus present at the end.

“We know the virus is alive and replicating if the second qPCR test detects a larger amount of the virus than the first one,” says Laflamme. “This new approach enables us to identify live virus an average of 25 days faster than with the traditional virus isolation protocol alone. Clients need to know whether a virus is dead or alive because the virus could pass through the gills of a fish but may not infect a fish.”

In June of 2016, the aquatic animal health lab at the Gulf Fisheries Centre achieved international accreditation, which means it meets the ISO-17025 standards for diagnostic laboratories established by the International Organization for Standardization. As with all tests performed by the National Aquatic Animal Health Laboratory System labs, the new protocol for ISAv testing must also undergo diagnostic validation for eventual inclusion on the scope of accreditation followed by ongoing monitoring to ensure it continues to provide accurate and precise results.

For more information, see:Fisheries and Oceans Canada’s National Aquatic Animal Health Laboratories Attain International Accreditation.”

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