A deadly fish virus has been found for the first time in fish from Lake Superior, meaning all Great Lakes are now known to be infected, Cornell University researchers said Wednesday, January 27.

Viral hemorrhagic septicemia

VHS) causes fatal anemia and hemorrhaging in many fish species, but poses no threat to humans. Biologists have been tracking the progress of the disease in fish populations for five years, with growing concerns that the virus would penetrate the entire Great Lakes basin. Until last week, when fish from Paradise and Skanee in Michigan and St. Louis Bay and Superior Bay in Wisconsin tested positive, it had not been detected in Lake Superior.

Fisheries managers with the Department of Natural Resources believe the virus likely was brought here from the maritime region of Canada in ballast water from large freighters between 2000 and 2002. While biologists acknowledged the eventual spread of the virus was inevitable throughout the lakes once it was introduced, their goal has been to monitor it and slow its spread enough to buy them time to learn how to manage the disease in the future to soften its impact on the sport fishing industry. The virus causes large fish kills in infected populations and is not treatable.

Regulations are already in place to prevent moving the virus from one body of water to another, so last week's findings will not lead to additional regulatory measures, according to the Cornell report. In 2008 the U.S. Department of Agriculture issued a federal order preventing transport of the 28 species in the Great Lakes watershed, including Lake Superior, to limit the spread of the disease among fish populations.

The virus caused no significant fish mortality in 2008 or 2009, and researchers are still studying the reasons for that.

"It is important to note that there are still fish harboring [the virus]; essentially the infection proceeds even though no mortalities are being observed," said Paul Bowser, professor of aquatic animal medicine at Cornell's College of Veterinary Medicine. "This is important because it suggests that these infected fish may serve as a reservoir for the virus in the Great Lakes ecosystem. While we don't fully understand the lack of recent mortality, the potential presence or absence of stressors on the fish may be playing a role."

The 2009 research work was funded by the Cornell Agriculture Experiment Station and United States Department of Agriculture's Animal and Plant Health Inspection Service. The U.S. Geological Survey Western Fisheries Research Center in Seattle was involved in the project.