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What You Need to Know about VHS -- a Vicious Killer Virus That is Silently Wiping Out Fish Populations

An unprecedented virus that targets numerous fish species and often kills the fish it infects is threatening fish species in the Great Lakes and beyond. Viral Hemorrhagic Septicemia (VHS) can kill more than 25 fish species and has already wiped out large numbers in many areas.

Viral Hemorrhagic Septicemia (VHS)

VHS is not transmittable to humans, and fish infected with VHS that aren't showing symptoms are still safe to eat and handle.

VHS has been around since the early '30s, when it was discovered in farmed rainbow trout in Europe. However, in 1988 the virus was discovered among wild herring and cod at the U.S. Pacific Coast, and later among other species on the Atlantic Coast and in Japan.

The virus was found in the Great Lakes between 2005 and 2006, where it caused huge fish kills in lakes Huron, St. Clair, Erie, Ontario, and the St. Lawrence River. It's thought that migrating fish or ballast water from ships may have brought in the virus.

Among the thousands of fish affected were muskies, walleye, lake whitefish, freshwater drum, yellow perch, gizzard shad, redhorse, round gobies and more.

The virus in so widespread that it is considered an invasive species in the Great Lakes, and is unusual because it's the first time a virus has affected so many different fish species in the Great Lakes, according to the Wisconsin Department of Natural Resources.

Because it affects such a large variety of fish, and often kills the fish it infects, fish biologists consider it a serious threat.

Is VHS a Threat to Humans?

VHS spreads among fish through urine and reproductive fluids released into the water, and also by eating other infected fish. Though it spreads rapidly among many fish species, it is not a threat to people.

Some fish can carry VHS and not show any outwardly symptoms. These fish are safe to handle and eat, according to WDNR, though the agency advises against eating any fish that show symptoms of being sick or diseased.

How Can I Recognize VHS in Fish?

Viral Hemorrhagic Septicemia (VHS)

To prevent the spread of VHS, emergency guidelines have been issued that advise not moving live fish (including minnows) from the water, emptying water from buckets and boats and cleaning your boat of any plant matter before leaving the shore.

Fish become infected with VHS through their gills, and the virus moves from there to internal organs and blood vessels. The virus weakens blood vessels causing hemorrhages in the internal organs, muscles and skin. Signs that a fish is infected include:

  • Hemorrhaging (bleeding)

  • Unusual behavior

  • Anemia

  • Bulging eyes

  • Bloated abdomens

  • A rapid onset of death

Meanwhile, some infected fish may show no symptoms at all, which is why it's important not to transport fish from affected lakes to other areas.

Preventing the Spread of VHS

VHS presents a huge threat to fish species across the country. It has already killed large numbers of fish, but biologists are concerned that if it reaches smaller inland waters it could spread even faster and cause even greater devastation to fish species.

Among the factors that increase the risk of an outbreak is stress, which, as in people, depresses the immune system and increases the risk of infection. Fish can become stressed from spawning, poor water quality, lack of food or being handled excessively.

Meanwhile, because the virus is easily transmitted by fish or water introduced to a new area, several states have issued the following emergency guidelines to people who are planning to fish in the Great Lakes or other affected areas:

  • Do not take live fish from the landing or shore (including unused bait minnows).

  • Put your catch on ice.

  • Before you leave the landing or shore, drain all water from bilges, bait buckets, live wells and other containers.

  • Purchase live minnows only from registered bait dealers, or catch them yourself in the same water you fish.

  • Inspect your boat and remove all visible plants and animals before launching and before leaving for the day.

The USDA's APHIS (Animal Plant Health Inspection Service) has also issued a federal order to prevent the spread of VHS into aquaculture facilities. The order prohibits the interstate transport of certain live fish species from eight states (Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin) and importation from the Canadian Provinces of Ontario and Quebec, except under certain conditions.

For now, no one knows for sure how far VHS will spread, but experts are optimistic that prevention measures will help.

"In a large ecosystem -- we're talking about the lower Great Lakes -- there really is no treatment," said Paul Bowser, professor of aquatic animal medicine at Cornell University. "The best management option is to try and contain the spread of it as best we can."

Recommended Reading

New Dangerous Tick-Borne Disease Another Reason to be Extra-Cautious This Tick Season

Dog Bites, a Shocking U.S. Epidemic (Especially Among Kids): How to Avoid, and What to Do


Wisconsin Department of Natural Resources

Cornell University Chronicle Online June 14, 2007

American Veterinary Medical Association

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