The latest invader of the largest freshwater system is spreading to surrounding waters, causing officials to enact emergency rules
By Bob Grant | May 24, 2007
A highly contagious and deadly disease that has plagued fish in the Great Lakes for at least two years is ravaging that lake system and has spread to fish in other freshwater lakes and rivers in the region, prompting officials to issue emergency rules and strengthen existing regulations to slow its march.
The virus, viral hemorrhagic septicemia virus (VHSV), is not native to the Great Lakes region, so it's hard to predict how damaging it will be to the area's fish, said Rod Getchell, who studies fish diseases at Cornell University's aquatic animal health program. "It's [infecting] naïve hosts, and it's a pathogen that's in a new environment,' he told The Scientist. "That's the scary part. We don't know what kind of effect it's going to have on populations.'
Many fish species die soon after being infected with VHSV, but the disease seems particularly virulent in the Great Lakes, where it has killed several hundred tons of fish over the past two years in Ohio, New York, and Michigan, according to USDA statistics.
The virus has already spread to the Saint Lawrence River, and managers fear that the disease could make its way into the Mississippi River drainage system.
Earlier this month, managers at the Wisconsin Department of Natural Resources discovered VHSV in two dead freshwater drum from Little Lake Butte des Morts, a small lake in northeastern Wisconsin that is part of the Lake Winnebago system.
Last week, Michigan Department of Natural Resources officials announced the presence of VHSV in black crappie, bluegill, and muskellunge that died in a large April fish kill in Budd Lake, a small water body on Michigan's lower peninsula.
This month, the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) amended a Federal Order specifying restrictions on the transport of fish between state and Canadian provinces known or suspected to harbor the virus. APHIS also issued an emerging disease notice last year detailing the extent of VHS incursion into U.S. inland waters.
State officials in Wisconsin and Michigan have also tightened restrictions on the translocation of fish and water between separate water bodies.
Last week, Wisconsin expanded its emergency rules, stressing that people drain all water from boats, buckets, and other containers before moving between water bodies, and prohibiting the translocation of bait fish from areas infected with the virus.
"Don't carry live fish out of these areas that we think are infected and don't bring any suspect bait into areas that we think are not infected,' Bill Horns, Great Lakes fisheries specialist with the Wisconsin Department of Natural Resources, told The Scientist.
VHS is not a threat to humans who handle or eat infected fish.
The virus has infected dozens of fish species from several families in the sprawling Great Lakes system and surrounding waters, and this disregard for taxonomic boundaries is one of the troubling aspects of the disease, said Getchell. "That just means that the virus can maybe infect every species. Recreationally important species, such as walleye and largemouth and smallmouth bass, have tested positive for VHSV, as have channel catfish, the most profitable aquaculture species in the U.S.
VHSV, an RNA rhabdovirus, has long been a problem for trout aquaculturists in Europe and has been documented in marine fishes on both the east and west coasts of North America.
The virus attacks endothelial tissues in host fish, causing hemorrhaging in blood vessels, eyes, and internal organs. It is shed through fish urine and feces, surviving for up to 14 days in water to infect the gill tissue of new hosts.
The Great Lakes form of the virus was detected in 2005, first in the Bay of Quinte, a narrow zigzagging channel on the Canadian side of Lake Ontario, and then in archived samples from fish caught in 2003 from Lake St. Clair, which straddles the U.S.-Canada border near Detroit. Additional Lake St. Clair fish tested positive for VHS in 2005.
Some experts suggest that the virus was introduced into the Great Lakes through bilge water offloaded from oceangoing vessels. One 2006 paper proposed that the Great Lakes isolate is a mutated form of VHSV seen in fish on the east coast of the U.S. and Canada.
The Great Lakes system is no stranger to invasive species, with non-native species like zebra mussels, rusty crayfish, and sea lamprey altering ecosystems there for years. Horns said that the updated VHSV regulations will help control the spread of other invasive species. "A lot of the things we're trying to do through our rule-making could just be called good boat hygiene or responsible resource management activities that can not only help prevent the spread of [VHSV], but other invasive species as well,' Horns told The Scientist.
Links within this article:
Wisconsin Department of Natural Resources
Freshwater Drum - Species Summary
Michigan Department of Natural Resources
Black Crappie - Species Summary
Bluegill - Species Summary
Muskellunge - Species Summary
USDA - APHIS, "Amended Federal Order viral hemorrhagic septicemia (VHS),' May 4, 2007.
USDA - APHIS, "Viral Hemorrhagic Septicemia in the Great Lakes,' Emerging Disease Notice, July 2006.
Michigan Department of Natural Resources, "Fish Disease Control'
Wisconsin Department of Natural Resources, "The Viral Hemorrhagic Septicemia virus (VHSV) in Wisconsin,' May 17, 2007.
USDA - APHIS, "Viral Hemorrhagic Septicemia (VHS) Virus (V)-Susceptible Species,' October 2006.
E. Elsayed et al, "Isolation of viral haemorrhagic septicaemia virus from muskellunge, Esox masquinongy (Mitchill), in Lake St Clair, Michigan, USA reveals a new sublineage of the North American genotype,' Journal of Fish Diseases, October 2006.
B. Palevitz, "The continuing saga of invasive species,' The Scientist, April 2002.
E. Russo, "Cooperation urged on invasives,' The Scientist, March 2004.