Novirhabdovirus sp. genotype IV sublineage b

Common Name: Viral Hemorrhagic Septicemia Virus (VHSV-IVb)

Synonyms and Other Names:

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Identification: VHS is an RNA virus with a bullet-shaped morphology typical of rhabdoviruses and a 11–12 kb nucleotide genome encoding five structural proteins. Viral particles are 170-180 nm in length and 60-70 nm in width (Skall et al. 2005; Elsayad et al. 2006). A classification based on sequences of N- and G-genes reveals four majorgenotypic groups that correspond to the geographical distribution of the virus: one group includes isolates from European inland waters and northern marine coastal areas, a second group is composed of marine isolates from the Baltic Sea, a third group comprises isolates from the North Sea, and a fourth group comprises North American isolates. Thus far, the virus has been found in Europe, North America, Japan and Korea (Nishizawa et al. 2002; Skall et al. 2005). Based on a comparison of the gene sequences of all North American VHS isolates, Elsayad et al. (2006) propose that the VHS isolate obtained from a muskellunge in Lake St. Clair constitutes a distinct sublineage of the North American genotype that likely originated on the east coast of North America.

The clinical signs of VHS differ depending on the course of infection. In the latent manifestation of the disease, some mortality may occur and fish become hyperactive, sometimes displaying nervous symptoms such as twisting of the body and behavior that involves swimming erratically in circles or in a corkscrew pattern (CFSPH 2003). Conversely, some carriers of the virus may show no symptoms at all (Dopazo et al. 2002). Histopathological changes occur in the liver, kidneys, spleen and skeletal muscle (McAllister 1990); the kidney and spleen appear to be the organs most often targeted by VHS virus (Brudeseth et al. 2002). In the acute form of the disease, fish become lethargic, dark and anemic, with bulging eyes, congested kidneys, mottled liver, and with hemorrhage in the eyes, skin, gills, fin bases, skeletal muscle and viscera (McAllister 1990). Mortality is very high and the disease is short-lived (CFSPH 2003). In the chronic form of the disease, mortality is low and all the symptoms are similar to the acute form, except that hemorrhaging is not common; instead, the liver, spleen and kidneys experience an accumulation of fluid such that the body becomes bloated and the liver and kidneys become very light in color (McAllister 1990). Survivors of infection can be carriers of the virus throughout the rest of their lives.

Size: approximately 170-180 nm long and 60-70 nm wide (Elsayad et al. 2006; McAllister 1990).

Native Range: Indigenous to eastern and western Europe, Japan, and the Pacific coast (from California to Alaska) and Atlantic coast of North America. Some evidence suggests that the European strains of VHS are native to the Atlantic Ocean. It is generally believed that all strains of VHS are derived from a common marine ancestor (Skall et al. 2005).

Based on a comparison of the gene sequences of all North American VHS isolates, Elsayad et al. (2006) propose that the VHS isolate obtained from a muskellunge in Lake St. Clair constitutes a distinct sublineage of the North American genotype (designated North American genotype IVb) that likely originated on the east coast of North America.

Map Key
This map only depicts Great Lakes introductions.

Great Lakes Nonindigenous Occurrences: This novel sublineage of the North American genotype IV  was first isolated from Muskellunge (Esox masquinongy) caught in the northwest part of Lake St. Clair (Elsayad et al. 2006). VHS has subsequently become established throughout much of the Great Lakes region.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Novirhabdovirus sp. genotype IV sublineage b are found here.

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IL200820081Lake Michigan
MI2003202413Black-Macatawa; Boardman-Charlevoix; Cheboygan; Dead-Kelsey; Detroit; Huron; Lake Erie; Lake Huron; Lake Michigan; Lake St. Clair; Lake Superior; Lone Lake-Ocqueoc; Tittabawassee
MN201020101St. Louis
NY2006201711Chautauqua-Conneaut; Headwaters St. Lawrence River; Irondequoit-Ninemile; Lake Erie; Lake Ontario; Lower Genesee; Niagara River; Oak Orchard-Twelvemile; Oswego; Salmon-Sandy; Seneca
OH200620101Lake Erie
WI200720218Door-Kewaunee; Lake Michigan; Lake Superior; Lake Winnebago; Lower Fox; St. Louis; Upper Fox; Wolf

Table last updated 7/19/2024

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: VHS occurs in both marine and freshwater environments. It requires an incubation period of approximately 7 to 15 days, depending on water temperature (CFSPH 2003). It becomes inactivated in ether, chloroform, glycerol, formalin, sodium hypochlorite, sodium hydroxide, iodophors, UV radiation, or by desiccation, or exposure to pH levels lower than 2.4 or higher than 12.2 (CFSPH 2003; McAllister 1990). VHS is still stable at a pH of 5.0, while the optimum replication pH is 7.4–7.8. The optimum replication temperature is 14–15°C, whereas replication is low at 6°C and almost nonexistent at 20°C (De Kinkelin et al. 1980; Bernard et al. 1983; McAllister 1990). The virus becomes inactive after 24 hours at 20°C in water, but can persist for five days at 4°–Cin water (CFSPH 2003). Consequently, fish mortality from VHS is greatest at 3–12°C and is very rare above 15°C (McAllister 1990).

Fishes are susceptible to infection at any age. VHS is transmitted to juvenile and adult fish most often via urine and sex products that enter a fish through secondary gill lamellae, or possibly through fin bases or via wounds; it cannot enter eggs and infect fish before hatching (McAllister 1990; Brudeseth et al. 2002; CFSPH 2003; Harmache et al. 2006). Juvenile fish are generally more susceptible than adults. Experiments have recorded infection after contact with infected fish and after immersion in infected water; the virus can remain activated in water for several days (McAllister 1990). The VHS virus can persist for long periods of time in the bottom of culture ponds, potentially in invertebrates (CFSPH 2003). There is evidence of infections transferred between farmed and free-living fishes in European inland waters and coastal areas (Stone et al. 1997; Skall et al. 2005).

The mortality rate for infected fish varies between 20% and 80%, depending on environmental conditions, and has reached 100% in trout fry (CFSPH 2003).

Means of Introduction: It is not known how VHS was initially introduced to the Great Lakes–St. Lawrence River system; however, genetic evidence suggests that the virus originated from the Atlantic coast of North America, possibly via transport in ballast water or infected migratory fishes (Elsayad et al. 2006). Recent study indicates that VHS distributions are not related to shipping or boating activity (Bain et al 2010).  Aquaculture activities are implicated in the spread of the virus (Skall et al. 2005; Fisheries Research Services 2006). The potential for transport with bait fish (reviewed by Goodwin et al. 2004) is demonstrated by the virus' recovery in cell culture from frozen Pacific Herring (Clupea pallasi) after two freeze/thaw cycles in a conventional freezer (Meyers et al. 1994). Waterfowl might also play a role in transmitting the virus (Peters & Neukirch 1986).  It appears that once VHSV is established in a region the virus will become widespread, hosted by fish without disease symptoms, and capable of persistence at low but detectable levels (Bain et al 2010).

Status: The North American strain of VHS virus is established in Lakes Ontario, Erie, St. Clair, Huron, Michigan, and Superior, as well as in the St. Lawrence River, with additional reports throughout the Great Lakes basin (Elsayad et al. 2006, MNDR 2010, Whelan 2009, Wren and Lee 2006, USDA 2006).

Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...



Novirhabdovirus sp. VHSV-IVb has a high environmental impact in the Great Lakes.
VHS is listed as a World Organization for Animal Health (OIE) reportable disease for aquatic animals (OIE 2012) and is also listed as a reportable disease in Canada (CFIA 2012).

VHSV-IVb has the potential to infect a wide range of fish species (Kim and Faisal 2010a) with clinical signs such as body twisting and erratic swimming (CFSPH 2003). Because of this, infected fish may be more susceptible to predation (Lafferty and Morris 1996), which could result in indirect effects on the food web and ecosystem. Die-offs of apex predators such as muskellunge and northern pike may have severe impacts on the Great Lakes food web.

The Great Lakes strain of the North American VHSV genotype (IVb)  is less virulent to salmon and trout species than the European strain (Kim and Faisal 2010b Follett et al. 1997) and has not caused large fish kills of these species in the Great Lakes to date (USDA and APHIS 2006). However, mortality of other species has been documented. Native and non-native species that are susceptible to this virus may  then aid in the virus transmission.

VHS is believed to have caused large die-offs of Freshwater Drum (Aplodinotus grunniens) in eastern Lake Ontario and Muskellunge (Esox masquinongy) in Lake St. Clair in 2005 (Faisal et al 2012, Wren and Lee 2006). In the spring and summer of 2006, VHS was implicated as a cause of large die-offs of Muskellunge in the Thousand Islands area of the St. Lawrence River (Wren and Lee 2006) and die-offs of Muskellunge, Northern Pike (Esox lucius), Gizzard Shad (Dorosoma cepedianum), Smallmouth Bass (Micropterus dolomieui), Walleye (Sander vitreus), and Yellow Perch (Perca flavescens) in Lakes St. Clair, Erie, and Ontario (USDA and APHIS 2006). Die-offs of Walleye in Conesus Lake, NY and Lake Whitefish (Coregonus clupeaformis) and Walleye in Thunder Bay in the fall of 2006 were also believed to have been caused by VHS (Faisal et al. 2012, Whelan 2009). In May 2007, low to moderate fish kills of Freshwater Drum were experienced in the Wisconsin lakes Butte des Mortes and Winnebago. Later that year, there was a die-off of sunfish (Family Centrarchidae) in the Seneca-Cayuga Canal, New York (Focus on Fish Health 2010). VHS has also been implicated as the cause of Lake Whitefish and Walleye die-offs in Lake Huron (MSG 2012).
Other Great Lakes native species that are susceptible to VHS and have experienced mild to moderate die-offs include Black Crappie (Pomoxis nigromaculatus) and Bluegill (Lepomis macrochirus) in Budd Lake, MI and Lake St. Clair, White Bass (Morone chrysops) in Lake Erie, and Rock Bass (Ambloplites rupestris) in Skaneateles Lake, NY (Whelan 2009). Die-offs of Largemouth Bass (Micropterus salmoides) have also been observed (Kim and Faisal 2010a, Kim and Faisal 2010b).

For the third consecutive year, the 2011 U.S. Fish and Wildlife Service Region 5 survey of 25 sites across the northeast U.S. and lower Great Lakes did not detect VHS among a total of 2,498 fish comprising 22 species (GLFHC 2012). However, that same year, VHSv was isolated near the Milwaukee Harbor from a fish kill of yearling Gizzard Shad in mid to late March and again in Yellow Perch in late June (GLFHC 2012). Overall, VHSv detection was low and low impacts were realized in the Great Lakes in 2011 (GLFHC 2012).

Great Lakes native species verified as susceptible to infection by VHSV-IVb include Silver Redhorse (Moxostoma anisurum) and Shorthead Redhorse (Moxostoma macrolepidotum) in Lake St. Clair, Burbot (Lota lota) in Lake Ontario, Channel Catfish (Ictalurus punctatus) in New York, and Emerald Shiner (Notropis atherinoides) in Lakes St. Clair and Erie and the Niagara River. However, as of 2009, no mortalities had been observed in these species (Whelan 2009). Lake Trout (Salvelinus namaycush) and Brook Trout (Salvelinus fontinalis) are also susceptible to the VHS virus, but mortalities have not been seen within the Great Lakes basin. This may be due to the fact that the North American strain appears to be of low pathogenicity to salmonids (Kocan et al. 1997, Meyers and Winton 1995, Skall et al. 2005).

Novirhabdovirus sp. VHSV-IVb has a high socio-economic impact in the Great Lakes.
Humans are not susceptible to VHS and there is no evidence that the virus can be transferred to humans by consuming infected fish (PFBC 2011).

Increased regulations (see Management) have limited the scope of operations for those in the bait/live fish industry and have cost a substantial amount of additional time and money to fulfill testing and certification requirements.

Despite the wide host range of the virus, effects on commercial and recreational fisheries related to die-offs have been relatively mild in the Great Lakes (Focus on Fish Health 2010).

As of June 2011, there has not been a recorded outbreak of VHS within a hatchery system in the United States. Under APHIS policy, total destruction and disinfection of a hatchery is likely if VHS is isolated, leading to significant economic loss (PFBC 2011).

European freshwater-strain VHS (genotype Ia) infection usually appears in salmonids, particularly Rainbow Trout (Oncorhynchus mykiss), which suffer high mortality rates. In Europe, economic losses due to the virus are estimated at 50 million Euros/year (Micol et al. 2005). However, while many commercially and recreationally-valuable salmonids—including Chinook Salmon (O. tshawytscha), Coho Salmon (O. kisutch), and Rainbow Trout (O. mykiss)—are susceptible to the Great Lakes strain of the virus (IVb), recent studies indicate they experience VHS-induced symptoms and mortality less often than other susceptible species (Al-Hussinee et al. 2010, Kim and Faisal 2010a). Recreationally-valuable species that have been particularly affected experimentally include Muskellunge (E. masquinongy) and Largemouth Bass (M. salmoides), both of which have experienced very high mortality rates (Kim and Faisal 2010a, Kim and Faisal 2010b).

There is little or no evidence to support that Novirhabdovirus sp. VHSV-IVb has significant beneficial effects in the Great Lakes.
VHS has caused die-offs of non-native species in the Great Lakes, including Round Goby (Neogobius melanostomus) (Wren and Lee 2006). In 2008, the first recorded die-off of Round Goby occurred in Lake Michigan, although observed signs of the virus had been documented in Lake Michigan in 2007 (Focus on Fish Health 2010). Die-offs of Common Carp (Cyprinus carpio) have been observed in Lake Ontario (Whelan 2009).


Regulations (pertaining to the Great Lakes)
Transportation of VHS-susceptible species out of New York, Pennsylvania, Ohio, Michigan, Indiana, Illinois, Wisconsin, Minnesota, Ontario, and Quebec is prohibited unless certain conditions are met (see below; USDA and APHIS 2008). International movement of VHS-susceptible species from the two infected Canadian provinces to the United States is permitted if the shipment meets certain requirements and is imported under an APHIS permit for direct slaughter, or during catch and release fishing activities (USDA and APHIS 2008).

Movement of VHS-susceptible species between VHS-infected or at risk states is permitted as long as fish are sent directly to state-inspected slaughter facilities that discharge waste water to a municipal sewage system that includes disinfection, or discharge to a non-discharging pond or a settling pond that disinfects according to all applicable U.S. EPA and state regulatory criteria, and are accompanied by a valid VS 1-27 (Permit for Movement of Restricted Animals) form issued by an APHIS area office. Remains from slaughter facilities must be rendered or composted (USDA and APHIS 2008).

Interstate movement of VHS-susceptible fish from VHS-infected or at risk states to non-infected states is permitted as long as the fish are accompanied by appropriate state, tribal, or federal documentation stating the fish have tested negative for the virus (USDA and APHIS 2008). Movement of VHS-susceptible species to state, federal, or tribal authorized research and diagnostic facilities is also permitted provided that the fish are accompanied by a valid VS 1-27 form issued by an APHIS area office and the remains are disposed of as medical waste adhering to all applicable U.S. EPA and state regulatory criteria (USDA and APHIS 2008).
New York, Pennsylvania, Ohio, Michigan, Indiana, Illinois, Wisconsin, and Minnesota have instated similar baitfish regulations to control the spread of VHS and other fish pathogens. Those of New York include that bait harvested from inland waters for personal use is only permitted to be used within the same body of water from which it was taken and cannot be transported overland (with the exception of smelt, suckers, alewives, and blueback herring). Once transported, baitfish cannot be replaced to its original body of water (NYSDEC 2012).

Live or frozen bait harvested from inland New York waters for commercial purposes is only permitted to be sold or possessed on the same body of water from which it was taken and cannot be transported over land unless under a permit and or accompanied by a fish health certification report. Bait that is preserved and packaged by any method other than freezing, such as salting, can be sold and used wherever the use of bait fish is legal as long as the package is labeled with the name of the packager-processor, the name of the fish species, the quantity of fish packaged, and the means of preservation (NYSDEC 2012).

Certified bait may be sold for retail and transported overland as long as the consumer maintains a copy of a sales receipt that contains the name of the selling vendor, date sold, species of fish sold, and quantity of fish sold. Bait that has not been certified may still be sold but the consumer must maintain a sales receipt containing the body of water where the bait fish was collected and a warning that the bait cannot be transported by motor vehicle. Bait sold for resale require a fish health certification along with a receipt that contains the name of the selling vendor, date sold, species of fish sold, and quantity of fish sold, which must be kept for 30 days or until all bait is sold (NYSDEC 2012).

In addition to baitfish protections, prior to placing fish in New York waters, a fish health certification report must document that the fish are VHS free.

Ontario has implemented management zones to help slow the spread of VHS. Commercial bait operators are prohibited from moving live baitfish out of the VHS Management Zone and live or dead bait in or out of the Lake Simcoe Management Zone. Salmon and trout eggs may be collected from virus-positive waters only if eggs are disinfected according to the Ministry’s protocol. Walleye spawn collection is permitted as long as the fish are stocked back into virus-positive waters. Fish and eggs are permitted to be stocked in waters that are not virus-positive only if the facilities are certified VHS free (MNR 2011).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

There are no known biological control methods for this species.

Multiple means of control are available to fish hatchery managers, including treatment of water with UVC (280-200nm wavelength) irradiation and heat (>15°C) (McAllister 1990), exposure to pH levels lower than 2.5 or higher than 12.2, desiccation of tanks and equipment (CFSPH 2007), minimization of stressors, cessation of water flow to adjacent waterways, and establishment of quarantines (CFSPH 2007, Warren 1983). Furthermore, exposure to VHS can be prevented through use of spring water, specific pathogen free (SPF) stock, and separate cultivation of salmonids and flatfish (CFSPH 2007).

As with other hitchhiking aquatic species, boaters and anglers are encouraged to clean and disinfect their gear (Bakal 2012), as well as to completely drain bilges and live wells before moving between bodies of water (MNR 2012).

The VHS virus is sensitive to ether, chloroform, glycerol, formalin, iodophor, sodium hydroxide, and sodium hypochlorite, which can be used as disinfectants (CFSPH 2003, McAllister 1990). No effective anti-viral agents or commercial vaccines exist (CFSPH 2007). Disinfection of live wells and other contaminated equipment can be accomplished with a 10% household bleach/water solution (e.g., 100 ml of household bleach to 900 ml of water). Waste water should be discarded away from any water body. Virkon® S is another widely available disinfectant (MNR 2012).

The U.S. Fish and Wildlife Service recommend implementation of the International Hazard Analysis and Critical Control Point (HACCP) planning standard to prevent the spread of VHS (Bakal 2012).
VHS should be reported to Area Veterinarians in Charge (AVIC) or state veterinarians immediately upon diagnosis or recognition of the disease. Fish health surveillance programs and fallowing are also useful methods of control (CFSPH 2007).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: A U.S. Federal Order aims to prevent the spread of VHS into aquaculture facilities by restricting the interstate movement and importation of live fish of VHS-susceptible species

References (click for full reference list)

Other Resources:
Author: Kipp, R.M., A. Ricciardi, A.K. Bogdanoff, and A. Fusaro.

Contributing Agencies:

Revision Date: 8/17/2018

Citation for this information:
Kipp, R.M., A. Ricciardi, A.K. Bogdanoff, and A. Fusaro., 2024, Novirhabdovirus sp. genotype IV sublineage b: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 8/17/2018, Access Date: 7/20/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.