TRAVERSE CITY - A fatal fish virus has been detected in Lake Superior for the first time, meaning it has spread to all the Great Lakes, researchers said Wednesday.
Cornell University scientists said they recently detected viral hemorrhagic septicemia, or VHS, while testing fish in the largest of the Great Lakes.
VHS has been identified in 28 freshwater fish species within the Great Lakes watershed since 2005, including popular sport and commercial varieties such as walleye, muskellunge and whitefish.
Although not dangerous for humans, the virus has caused large fish kills in Lakes Ontario, Erie and Huron. It also has turned up in Lake Michigan.
Even so, officials in Michigan and Wisconsin said Wednesday there was no evidence of a widespread outbreak in Lake Superior. They said the Cornell findings would not lead to any immediate changes in boating or fishing regulations.
Both states already limit movement of bait fish and have other rules aimed at preventing VHS from spreading.
''VHS remains a threat to all the Great Lakes, and we will increase our efforts to slow the spread through public awareness of the simple things boaters and anglers can do to help,'' said Rebecca Humphries, director of the Michigan Department of Natural Resources and Environment.
VHS causes bleeding, bloated abdomens and bulging eyes in fish before finally killing them. Scientists are unsure how the exotic species arrived in the Great Lakes, although it may have been carried by migrating fish or been carried in ballast water of oceangoing ships.
The U.S. Department of Agriculture prohibited interstate transport of the 28 vulnerable species in 2008. Phyllis Green, superintendent of Isle Royale National Park, ordered vessels in 2007 not to dump untreated ballast waters near the island, home to the rare coaster brook trout.
The Cornell researchers teamed with the U.S. Geological Survey for their study. They tested 874 fish for signs of VHS.
Fish tested positive for trace amounts at four locations: Paradise and Skanee in Michigan and St. Louis Bay and Superior Bay in Wisconsin.
The finding makes it clear that ''the infection proceeds,'' although no significant die-offs from VHS were seen the past couple of years in the Great Lakes region, said Paul Bowser, professor of aquatic animal medicine at Cornell, in a news release.
''This is important because it suggests that these infected fish may serve as a reservoir for the virus in the Great Lakes ecosystem,'' Bowser said.
State officials said it was understandable that VHS would have worked its way into Lake Superior, which is connected to Lake Huron by the St. Marys River.
''We're disappointed with Cornell's finding but not surprised,'' said Matt Frank, director of the Wisconsin Department of Natural Resources.