|VHS Virst Threatens the Great Lakes|
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Viral hemorrhagic septicemia (VHS) is a serious disease among fish in geographical areas including the Great Lakes basin, where 28 species of freshwater fish are known to be infected.
Based-on mortality rates, VHS is one of the most life-threatening diseases for ﬁsh. “There are no effective treatments or ways to control it. There is a wide diversity of ﬁsh species that can be affected,” says Paul R. Bowser, Ph.D., professor of Aquatic Animal Medicine in the Aquatic Animal Health Program of the Department of Microbiology and Immunology at Cornell University’s College of Veterinary Medicine.
In aquatic creatures, VHS causes anemia and hemorrhaging, leading to bleeding by destroying cells lining blood vessels, and then destroying internal organs, such as the heart, kidneys, liver and spleen. The ﬁsh then dies. This is due to the ability of the virus to take control of the metabolic machinery of cells inside a ﬁsh to replicate itself using ribonucleic acid or RNA.
VHS had been found in all of the Great Lakes but Lake Superior through 2008, and, in 2009, was discovered in Superior by Cornell University and the U.S. Geological Survey’s Western Fisheries Research Center, collaborating laboratories. Bowser’s research group collected ﬁsh from 30 sites, from the St. Lawrence River to northern Lake Huron. They found VHS in at least some of the ﬁsh in 21 of the 30 locations in 2008. “There was no association between the collections' site types (commercial harbor, recreational marina or undeveloped site[s]) and the presence of VHSV in ﬁsh that were collected in 2008. … None of the ﬁsh we collected showed any signs of disease that might commonly be seen with VHSV,” Bowser states.
The discoveries of the virus indicate a threat to the $1.4 billion sportﬁshing industry in New York. The virus continues to exist in ﬁsh in the Great Lakes, despite the lack of any noticeable deaths from the virus in these bodies of water in 2008 or 2009.
The history of the virus includes discoveries of it within rainbow trout raised in fresh water in the 1930s. Since then, different versions of the virus have been found in areas including Europe, Japan, Korea, off the Atlantic coast of maritime Canada, in the Paciﬁc Northwest in North America, and, of course, in the Great Lakes.
An extremely large number of infections from the virus occurred with freshwater drum. In 2006, several million pounds of ﬁsh died in Lake Erie, 99.9% of which were freshwater drum, according to Bowser. “This was likely the largest VHS mortality event,” he states. Scientists investigated from the U.S. Fish & Wildlife Service in LaCrosse, Wis. The mortality event likely occurred because of particular sensitivity to VHS and possibly environmental factors, including high temperatures. In addition, several hundred tons of freshwater drum perished in the summer of 2005 in Lake Ontario, according to the U.S. Department of Agriculture/Animal and Plant Health Inspection Service, www.seagrant.sunysb.edu/Images/Uploads/PDFs/fall07-vhs.pdf.
Other ﬁsh species that have experienced large numbers of die-offs from VHS include bluegill crappie, blunt nose sucker, gizzard shad, northern pike, pike ﬁsh muskellunge, redhorse sucker, round goby, smallmouth bass, walleye, white bass and yellow perch.
Some ﬁsh species are more susceptible to being infected than others. “Stress in the environment can make it worse,” Bowser says. The primary sources of stress thought to be associated with VHS disease events occur in the spring: spawning, which only occurs once each year; warming and often rapidly changing water temperatures; and the emergence of ﬁsh from the winter season with immune systems suppressed due to low water temperatures. Other stressors can include very, very heavy rains, which can cause the water to become murky; and oxygen depletion from algae blooms and die-offs.