Dr. Fred Kibenge, one of the world’s leading authorities on infectious salmon anaemia (ISA), will testify this week at the Cohen Commission of Inquiry into the Decline of Sockeye Salmon in the Fraser River.
Dr. Kibenge is Professor of Virology and OIE expert on ISA at the University of Prince Edward Island’s Atlantic Veterinary College (AVC). His lab at AVC is one of two ISA reference laboratories in the world designated by the World Organisation for Animal Health (OIE).
The Cohen Commission will hold three days of hearings December 15, 16 and 19 in Vancouver to hear new information about recent tests which indicate the possible presence of ISA virus (ISAv) in BC salmon.
Currently, testing for ISAv is done using RT-PCR, an internationally recognized and highly sensitive test that screens tissue samples to see if viral genetic material — or viral sequences — indicative of a particular virus is present. Each virus has a unique genetic sequence, and the test determines whether that sequence is present in a sample.
“It is important to note that the presence of ISAv sequences in tissue samples does not necessarily mean that the actual disease, ISA, is present in the subject fish or that ISA is present in the area where the fish were collected,” said Dr. Kibenge. “Viral material can be present in animals without them actually having the associated disease. In order to confirm whether an infectious viral disease is present, further testing is required.”
The OIE definition (confirmation) of ISAv infection requires that the virus be successfully grown in cell culture. Thus, the PCR test should be viewed as a highly sensitive screening test that, if positive, is only the first diagnostic step in documenting an ISAv infection, should one exist.
“There is much yet to discover and learn about ISAv, including possible effects, if any, it may have on wild fish,” said Dr. Kibenge. “The origin of ISA is not clearly known, but it is likely an existing virus that adapted to a new host. ISAv has been identified in healthy salmon and trout in the wild, with the first detection reported in 2001 in Scotland in a survey that was initiated after the first occurrence of ISA in Scotland in 1998. Other wild fish species such pollock and Atlantic cod can also carry the virus, but ISA disease outbreaks have only been seen in farmed Atlantic salmon.
“Surveillance for ISAv in wild fish is not widespread, and there are very few publications, peer-reviewed or otherwise, on this subject. Current diagnostic tests, which were developed in the context of farmed species, simply may not be conclusive of infections in wild fish. For that reason, further testing and research are necessary.”