A devastating virus that has killed thousands of fish in the Great Lakes over the past few years is different from other strains of the same virus found in Europe and the West Coast of the United States, according to new genetic research by the U.S. Geological Survey. The Great Lakes' strain of viral hemorrhagic septicemia virus (VHSV) is the only strain outside of Europe that has been associated with significant die-offs of freshwater fish species.
VHSV is a rhabdovirus that is the causative agent of one of the most dangerous viral diseases of fish, said Dr. Jim Winton, a fisheries scientist at the USGS Western Fisheries Research Center (WFRC) in Seattle. The virus belongs to a family of viruses that includes rabies. The disease causes internal bleeding in fish, but is not harmful to people.
Winton and co-authors Gael Kurath and William Batts recently authored a new USGS fact sheet that describes important genetic information about isolates of VHSV from Great Lakes region (see http://wfrc.usgs.gov/pubs/factsheetpdf/vhsfs2011108.pdf). Other strains of the VHS virus are found in continental Europe, North Pacific Ocean, North Atlantic Ocean, Baltic Sea and North Sea.
"This Great Lakes strain appears to have an exceptionally broad host range," said Winton. "Significant die-offs have occurred in muskellunge, freshwater drum, yellow perch, round goby, emerald shiners and gizzard shad."
Genetic research at the WFRC and by colleagues from Canada showed that this strain of the virus was probably introduced into the Great Lakes in the last 5 to 10 years, and that the fish die-offs occurring among different species and in different lakes should be considered as one large ongoing epidemic. The USGS genetic research also indicated that the Great Lakes' strain of the virus was not from Europe, where three other strains of the virus occur, but more likely had its origin among marine or estuarine fish of the Atlantic seaboard of North America. The strain is genetically most like samples of VHSV recovered during 2000-2004 from diseased fish in areas of New Brunswick and Nova Scotia, Canada.
The Great Lakes' strain has now been isolated from more than 25 species of fish in Lake Michigan, Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario, Saint Lawrence River and from inland lakes in New York, Michigan and Wisconsin. Experts fear the disease could potentially spread from the Great Lakes into new populations of native fish in the 31 states of the Mississippi River basin. Also, if VHS virus is introduced into the aquaculture industry, it could lead to trade restrictions as well as direct losses from the disease.
Regulatory agencies in the United States and Canada have already placed restrictions on the movement of fish or fish products that could pose a risk for the spread of VHS virus to regions outside of the known geographic range. These restrictions include requirements for viral examinations by standard methods.
For information on how to detect and confirm VHS virus, see http://biology.usgs.gov/faer/documents/VHSV_fs2007.pdf.