Viral hemorrhagic septicemia (VHS) is a deadly fish virus that is considered to be one of the most serious diseases of trout and salmon in freshwater environments in Europe. Outbreaks of the VHS virus can result in severe fish mortality events in commercial aquaculture practices as well as in wild populations, and can often have serious socio-economic consequences. For these reasons, VHS is listed as a reportable disease by the World Organization for Animal Health (OIE).

Fish infected with VHS may exhibit minor external hemorrhaging in the form of red pin-point spots or larger patches, particularly around the head. However, some infected fish may not exhibit any external signs at all. Internally, organs often display multiple hemorrhages, particularly in the liver, spleen, intestines and swim bladder. Sick fish often appear lethargic, swim in circles, or lie motionless just below the water surface. Although not all infected fish develop the disease, they can be carriers and have the ability to spread the disease to other fish.

For more detailed information on VHS, click here for a Vermont Fish & Wildlife report.

Scientists are not sure how the virus arrived in the Great Lakes. Like many Aquatic Invasive Species, it may have been introduced through infected fish or water dumped from the ballast tanks of ships from Europe. It may have arrived through infected fish migrating from the Atlantic Coast.

It has been determined that the strain of VHS now found in the Great Lakes region is most similar to that previously isolated from the Atlantic coast of North America, but it has been categorized as a unique strain of the virus. It is possible this is a mutated form of the Atlantic Ocean isolate.

From the time it was first discovered in Lake Ontario in 2005, the VHS virus has spread rapidly to other Great Lakes waters. It is now found in the St. Lawrence River, Lake Erie, the Niagara River, Lake St. Clair, the Detroit River, Lake Huron, and Lake Michigan. It has also spread to several inland waters (waters without any direct connection to the Great Lakes) including Lake Butte des Morts and Lake Winnebago in Wisconsin, Budd Lake in Michigan, and several lakes and rivers in the Finger Lakes region of New York.

Click here for a timeline of VHS spread in the Great Lakes

Click here for a map showing the current distribution of VHS in the Great Lakes region

The most probable way the virus moved through fish populations in the Great Lakes is through natural movement of infected fish. The virus most likely spread from the Great Lakes to inland waters through the capture and movement of live fish such as baitfish, and the transfer of contaminated water from one waterbody to another.

Although VHS has not yet been discovered in Vermont, the chance of it being spread here through live fish and overland boat movement is very real!

VHS is not a threat to people who handle or eat infected fish. However, it does pose a real threat to the many species of Vermont fish it can kill. This virus is unique in that it is the first fish virus known to affect so many different fish species.

There are 37 fish species known to be susceptible to the VHS virus, 26 of which are found in the Great Lakes. There are 24 species in Vermont that are susceptible to this fish disease. New fish species are being found that can carry the virus each year.

• Black crappie Pomoxis nigromaculatus*
• Bluegill Lepomis macrochirus*
• Bluntnose minnow Pimephales notatus*
• Brown bullhead Ictalurus nebulosus*
• Brown trout Salmo trutta*
• Burbot Lota lota*
• Channel catfish Ictalurus punctatus*
• Chinook salmon Oncorhynchus tshawytscha
• Coho salmon Oncorhynchus kisutch
• Emerald shiner Notropis atherinoides*
• Freshwater drum Aplodinotus grunniens*
• Gizzard shad Dorosoma cepedianum*
• Largemouth bass Micropterus salmoides*
• Muskellunge Esox masquinongy*
• Northern pike Esox lucius*
• Pumpkinseed Lepomis gibbosus*
• Rainbow trout Oncorhynchus mykiss*
• Redhorse sucker Moxostoma spp*
• Rock bass Ambloplites rupestris*
• Round goby Neogobius melanostomus
• Smallmouth bass Micropterus dolomieu*
• Walleye Sander vitreus*
• White bass Morone chrysops
• White perch Morone americana*
• Whitefish Coregonus spp*
• Yellow perch Perca flavescens*
• Spottail shiner Notropus hudsonius*
• Trout-perch Percopsis omiscomaycus*

* = Species known to occur in Vermont

The VHS virus is readily transmissible to fish of all ages, and survivors of infection can become lifelong carriers. The virus is shed from infected fish in urine, feces, and reproductive fluids, and transmission can occur through the water or by direct contact with infected fish, or contact with infected equipment.

The virus can persist in water in an infective state without a fish host for up to 14 days. It has also been documented that the virus is not always killed by freezing infected fish. In a hatchery or fish holding facility, transfer of the VHS virus on contaminated surfaces of gear and equipment presents a substantial hazard.

Healthy fish can also be infected when they eat an infected fish. Infected fish and water can easily spread the virus if they are released into a new water body. It is important that anglers, boaters and other water users do not move fish and water from one waterbody to another.

VHS cannot be transmitted through the feces of birds that eat infected fish since the virus cannot survive being passed through a birds' digestive system. Studies in Europe have shown that the European strain of VHS can survive on the feathers or feet of birds that have come in contact with infected fish or water. However, this method of spread is unlikely as it would take many trips of birds between infected and uninfected waterbodies to transfer and create the concentrations of the virus needed in the water to infect fish.