OREGON STATE UNIVERSITY

OSU scientists studying exotic virus that threatens fish

10/28/1998

NEWPORT - Scientists at Oregon State University's Hatfield Marine Science Center in Newport have discovered a new threat to Oregon fish - an exotic virus.

Hundreds of young tomcod, Pacific cod and walleye pollock caught in Puget Sound last spring were found to be infected with the North American strain of the hemorrhagic septicemia virus. The virus is a variant of the European trout virus previously found in Pacific herring and cod from Alaska to Washington.

Paul Reno, a microbiologist with OSU's Coastal Oregon Marine Experiment Station, said the fish were caught near Port Townsend, Wash., and brought to the Hatfield center last summer. They were to be used by the National Marine Fisheries Service in an ongoing 10-year study into the behavior of juvenile walleye pollock.

However, it was clear almost immediately that the fish were sick, and their disease was quickly diagnosed as the hemorrhagic septicemia virus. As soon as marine fisheries scientists determined the cause of the sickness was this disease, the fish were killed painlessly with an overdose of anesthetic added to their water. This was done to prevent the spread of the infection. Follow-up tests by pathologists showed that 90 percent of the fish that were destroyed already had the virus.

Humans can't contract this virus, but in fish it acts much like the human Ebola virus, which causes massive internal bleeding. In fish, it is suspected of weakening the blood vessels, allowing blood to seep between organs. The fish usually dies slowly from suffocation because its blood is no longer pumping oxygen to its vital organs, resulting in tissue death that ultimately is fatal.

The discovery of the virus strain has concerned the Oregon Department of Fish and Wildlife, which up to now has not officially documented a case of the virus in Oregon waters.

Rich Holt, a senior fish pathologist with the fish and wildlife department, said that because the virus has been found in cod or herring from Alaska to Washington, it is suspected of also being in Oregon waters, although this had not yet been documented.

ODFW has not been able to discover to what extent this might be a threat to stocks of wild fish and to the fisheries that depend on them, but apparently the discovery carries a slight threat to salmon as well: They feed on herring and other species susceptible to the virus. But how great a threat to salmon is another question.

Further research will be necessary to see if there is a way to prevent either the virus or its spread.