What is VHS? – Facts about Viral Hemorrhagic Septicemia virus
Viral Hemorrhagic Septicemia (VHS) virus was diagnosed for the first time
ever in the Great Lakes as the cause of large fish kills in lakes Huron, St.
Clair, Erie, Ontario, and the St. Lawrence River in 2005 and 2006. Thousands
of muskies, walleye, lake whitefish, freshwater drum, yellow perch, gizzard
shad, redhorse and round gobies died. Many Chinook salmon, white bass,
emerald shiners, smallmouth bass, bluegill, black crappie, burbot, and
northern pike were diseased but did not die in large numbers.
The VHS virus is not a threat to people who handle infected fish or want to
eat their catch, but it can kill more than 25 fish species. This is the
first time a virus has affected so many different fish species from so many
fish families in the Great Lakes. VHS virus is considered an invasive
species (not native to the Great Lakes), but scientists are not sure how the
virus arrived. It may have come in with migrating fish from the Atlantic
Coast, or may have hitch-hiked in ballast water from ships.
Skin hemorrhages (bleeding) on a fish infected with Viral Hemorrhagic
Septicemia virus (VHSv)© Garth Traxler (USGS, Seattle WA)
History of the VHS virus
VHS was first known as a disease of farmed rainbow trout in Europe as early
as the 1930’s. However, it was not until 1963 that scientists confirmed the
disease was caused by a virus. In 1988-89, the virus was detected in wild
herring and cod from the U.S. Pacific Coast, and also in salmon and
steelhead that returned to Washington hatcheries to spawn. Since then, the
virus has been confirmed in several species on the Atlantic Coast and in
Transmission of the Virus and Environmental Factors
Infected fish shed the virus in their urine and reproductive fluids. The
virus can survive in water for at least 14 days. Virus particles in the
water infect gill tissue first, and then move to the internal organs and the
blood vessels. The blood vessels become weak, causing hemorrhages in the
internal organs, muscle and skin. Fish can also be infected when they eat an
infected fish. Fish that survive the infection will develop antibodies to
the virus. Antibodies will protect the fish against new VHS virus infections
for some time. However, the concentration of antibodies in the fish will
drop over time and the fish may start shedding virus again. This may create
a cycle of fish kills that occurs on a regular basis.
The virus grows best in fish when water temperatures are 37-54 degrees F. Most
infected fish will die when water temperatures are 37- 41 degrees F, and rarely die
above 59 degrees F. Stress is an important factor in VHS outbreaks. Stress
suppresses the immune system, causing infected fish to become diseased.
Stressors include spawning hormones, poor water quality, lack of food, or
excessive handling of fish.
Signs a fish has VHS
The clinical signs of VHS may include hemorrhaging (bleeding), unusual
behavior, anemia, bulging eyes, bloated abdomens, and the rapid onset of
death; however, these symptoms could apply to many different fish diseases.
VHS must be confirmed by lab tests. Additionally, some infected fish may not
show any signs and transporting these fish to new locations could spread the
disease to new waters.
The clinical signs of VHS include hemorrhaging in the muscle tissue and
internal organs, pale organs, and bulging eyes.
© Dr Jim Winton (USGS, Seattle WA), Dr Mohamed Faisal (MSU, Lansing MI) and
Dr Paul Bowser (Cornell, Ithaca NY)
What can you do to prevent the spread of the VHS virus?
- Do not move live fish from one location to another. All fish
(including bait fish) should be dead before leaving the landing.
- Drain all water from your boat, trailer, containers, and fishing
equipment including bait buckets and coolers
- Report fish kills to your local fisheries biologist or conservation warden
For specific information on the VHS virus, please contact:
Fish Health Specialist