Fisheries and Oceans Canada Validates Diagnostic Tests for Detecting Cyprinid Herpesvirus 3 in Common Carp and Koi
Carp account for more than 70 percent of the farmed freshwater fish production in the world, with most of the carp aquaculture occurring in Eastern Europe and Asia. In recent years, however, world production of Common Carp (Cyprinus carpio L)—including ornamental koi—has taken a significant hit from cyprinid herpesvirus 3 (CyHV-3), which is responsible for the highly contagious koi herpesvirus disease (KHVD). According to the Food and Agriculture Organization of the United Nations, the disease has had a significant negative impact on a key food source as well as employment in many countries.
Cyprinid herpes virus-3
Spurred by the global fish trade and international ornamental koi shows, the disease has spread to most regions of the world and is listed as a notifiable disease by the World Organisation for Animal Health (OIE). In Canada, known or suspected cases of KHVD must be reported to the Canadian Food Inspection Agency (CFIA), which co-delivers the National Aquatic Animal Health Program (NAAHP) with Fisheries and Oceans Canada (DFO).
Outbreaks of koi herpesvirus disease have been observed in populations of farmed carp and koi as well as in wild carp. Clinical signs include white patches on the skin and gills, hemorrhages, lethargy, lack of appetite, sunken eyes, and erratic swimming. The last known natural outbreak of KHVD in Canada occurred in 2008, resulting in the death of thousands of wild Common Carp in Lake Manitoba.
World Trade Organization (WTO) agreements require Canada and other member countries to ensure that imports and exports of fish and seafood products are free of infectious aquatic pathogens (disease-causing agents). To protect Canada’s reputation for high-quality fish and seafood, the DFO National Aquatic Animal Health Laboratory System (NAAHLS), a key component of NAAHP, is responsible for delivering accurate and reliable diagnostic testing for aquatic animal pathogens, as well as targeted research and scientific advice in support of aquatic animal health.
Lab accreditation and test validation
In September 2014, the NAAHLS aquatic animal health lab at the Freshwater Institute in Winnipeg, Manitoba, achieved ISO17025 accreditation, which means it meets the requirements established by the International Organization for Standardization (ISO) for diagnostic laboratories. Each diagnostic test that the lab has on its scope of accreditation must be evaluated for its intended use. In scientific circles, this process is called “validation.”
“NAAHP decided to use a molecular biology technique called quantitative polymerase chain reaction (qPCR) to screen for CyHV-3,” says DFO research scientist Dr. Sharon Clouthier of the Freshwater Institute. These types of tests are designed to identify the genetic material of the target virus, and are particularly useful for detecting viruses that are difficult to grow in the lab.
Clouthier, the reference lab expert for this virus in Canada, led a four-year evaluation process to determine the “fitness” or suitability of an existing CyHV-3 qPCR screening method for use as a diagnostic test by NAAHLS.
“The validation process provides confidence that the analytical and diagnostic performance of a test is suitable for its intended purpose,” says Clouthier. In this case, the ultimate goal is to support the protection of wild carp populations, maintain access to international trade markets for Common Carp producers and koi breeders and hobbyists around the world and provide confidence to consumers that the products they purchase are free of the virus.
The multi-phase validation process involved:
- modifying an existing CyHV-3 qPCR test in-house to optimize its performance;
- assessing the test’s analytical performance—the minimum quantity of the target that the test can detect and the ability of the test to distinguish target from non-target material;
- evaluating the test’s diagnostic performance including its precision and accuracy. Precision refers to how consistent the test performs within a lab (repeatability) and between labs (reproducibility). Accuracy refers to the ability of a test to produce the correct result—i.e. the probability that a virus-positive sample will test positive (sensitivity) and that a virus-negative sample will test negative (specificity).
Clouthier expects to publish a paper on the validation study in a peer-reviewed journal sometime in 2016, and the lab looks forward to adding this method to its scope of accreditation. Nonetheless, scientists around the world are already using this for approach for research into the biology of CyHV-3. Dr. Clouthier herself is also applying it to a study of the virus in Common Carp from Lake Manitoba. The findings of this and other research may provide more insights into the ecology and evolution of CyHV-3 in wild populations of carp.
For more information, see: “Fisheries and Oceans Canada’s National Aquatic Animal Health Laboratories Attain International Accreditation.”
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