Viral Hemorrhagic Septicemia (VHS)
VHS is an infectious disease of fish. There are several strains of VHS that affect fresh and salt water fishes. The strain of VHS that is currently present in the Great Lakes is a strain most closely related to one that is found on the Atlantic coast. VHS affects several different species of fish, including sportfish. Some of the affected species include: Muskellunge (Esox masquinongy), Largemouth Bass (Micropterus salmoides), Freshwater Drum (Aplodinotus grunniens), Round Goby (Apollonia melanostomus), and Walleye (Sander viteus).
Species affected by VHS
Atlantic cod (Gadus morhua)
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)
Chum salmon (Oncorhynchus keta)
Emerald shiner (Notropis atherinoides)
Freshwater drum (Aplodinotus grunniens)
Gizzard shad (Dorosoma cepedianum)
Grayling (Thymallus thymallus)
Haddock (Gadus aeglefinus)
Herring (Clupea spp)
Japanese flounder (Paralichthys olivaceus)
Largemouth bass (Micropterus salmoides) |
Muskellunge (Esox masquinongy)
Pacific cod (Gadus macrocephalus)
Pike (Esox lucius)
Pink salmon (Onchorhynchus gorbuscha)
Pumpkinseed (Lepomis gibbosus)
Rainbow trout (Oncorhynchus mykiss)
Redhorse sucker (Moxostoma spp)
Rock bass (Ambloplites rupestris)
Rockling (Onos mustelus)
Round goby (Neogobius melanostomus)
Smallmouth bass (Micropterus dolomieu)
Sprat (Sprattus spp)
Turbot (Scophthalmus maximus)
Walleye (Sander vitreus)
White bass (Morone chrysops)
White perch (Morone Americana)
Whitefish (Coregonus spp)
Yellow perch (Perca flavescens) |
Characteristics
Clinical signs of VHS in fish varies greatly, where some fish will show obvious signs of the virus and others will show none. Severity of infection can be broken down into three different forms, acute (rapid onset), chronic (long lasting), and latent (dormant).
Acute infection usually results in rapid mortality (death). Signs of acute VHS infection include lethargy, darkening in color, protruding eyeballs, and anemia (red blood cell deficiency). Hemmoraging (bleeding) is also common in acute cases of VHS, it can be seen externally in the fish’s eyes, skin, gills, and fins. Internally small hemorrhages can be seen in some of the tissues surrounding the eyes, muscles attached to the skeleton, swim bladder and organs. The organs most commonly affected include the liver and kidneys, with the liver appearing mottled in color and engorged with blood. The kidneys in VHS infected fish appear thin and red.
Chronic infection also results in high mortality, however the period between infection and death is longer than in acutely infected fish. Chronically infected fish show lethargy, darkening of pigmentation, protruding eyeballs, and severe anemia. Unlike acute infection, chronically infected fish do not show the excessive external hemorrhaging, but do show a notably distended abdomen. Internally, VHS chronically infected fish show alterations to the liver, kidney, and spleen. The liver often shows small red spots on the surface, and the kidneys appear grayish in color. The infected fishes gills will also often appear pale in color
Latent infections show very low total mortality, with no clinical symptoms being observable. Although these fish do not show any external signs of the virus, they are still capable of passing the disease on to other fish.
The final cause of death in VHS infected fish is usually kidney failure, which results in fluid and waste products building up in their bodies. Another cause of death in infected fish is an inability to osmoregulate, meaning that the fish is unable to maintain the proper balance of fluids in their body.
Distribution
The strain of VHS that has been seen in the Great Lakes is a mutation of a VHS strain that has been documented on the Atlantic coast. In the Great Lakes region VHS has been found in the St. Lawrence River, Lake Ontario, the Niagara River, Lake Erie, the Detroit River, Lake St. Clair, Lake Michigan, and Lake Huron. It has also been found in two inland lakes in Wisconsin (Lake Winnebago) and Michigan (Budd Lake). It is unknown exactly how the virus gained entry to the Great Lakes. Ballast water of ocean going ships, aquarium/live fish releases, or hitching a ride on migrating fish are potential vectors for its introduction.
Ontario's Viral Hemorrhagic Septicemia Management Zone
VHS Management Zone ( December 2009 )
To slow the spread of Viral Hemorrhagic Septicemia (VHS) in Ontario, the Ministry of Natural Resources established a VHS Management Zone.
The VHS Management Zone contains the VHS virus-positive waters of lakes Ontario, Erie and Huron (including Georgian Bay) and their connecting waterways and tributaries up to the first barrier impassable to fish (excluding fishways).
In the VHS Management Zone, the Ministry of Natural Resources has taken additional steps to slow the spread of VHS, including:
- Restrictions on where bait fish are transported
- Restrictions on the collection of walleye, trout and salmon eggs from virus-positive waters, including a requirement for egg disinfection according to the ministry’s protocol, and restrictions on where stocking may occur based on the risk of spreading VHS.
Source: Ontario Ministry of Natural Resources website ( http://www.mnr.gov.on.ca/en/index.html )
Transmission/Impact
VHS is a highly contagious disease of fresh and saltwater fishes. VHS is transmissible to fish of all ages, and a number of different species. Transmission of the virus can occur in different ways, fish to fish transfer can occur by contact with one infected fish to another fish, or shed with bodily fluids. Virus can be spread from one waterbody to another through the movement of fish, water, boats, or equipment that has come in contact with the virus.
VHS implicated fish kills are most common in the spring and fall when water temperatures are cooler, with the optimum temperature for VHS replication being in the 14-15°C (57-59°F) range. VHS replicates slowly below 6°C (43°F), and little to no replication occurs at or above the 20°C (68°F) mark.
VHS Fact Sheets
Mortality varies by species and environmental conditions. Stress appears to increases the likelihood of infection. Mortality occurs most often during these stressful times, such as near spawning time, or towards the end of winter. Outbreaks of VHS can also occur during stressful environmental events, such as changes in water temperature or other environmental alterations. Different species of fish show varying degrees of mortality, and much is still unknown.
Although it is too early to tell what the impact will be on the fishery in the Great Lakes, large fish kills of certain species have already been observed. The Great Lakes fishery represents an estimated annual 4 billion dollar (US dollars) industry, and VHS has the potential to impact this industry greatly.
There is no indication that consuming or handling VHS contaminated fish poses any threat to human health. However hand washing is always good practice when handling fish and wildlife that show disease symptoms of any kind.
Help Prevent VHS from Spreading
These actions will help stop the spread of VHS and other fish diseases.
For Further Information:
Ontario Ministry of Natural Resources
Natural Resource Information Centre
1-800-667-1940
For reporting fish die-offs, please call
1-866-929-0994
