Common Name: Largemouth bass virus (LMBV)

Synonyms and Other Names:

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Identification: The largemouth bass virus is an icosahedral-shaped particle without an envelope. It occurs in the cytoplasm of host fish cells. When it passes out of the plasma membrane of the host fish cell, it acquires an envelope (Plumb et al. 1996).

In Largemouth Bass (Micropterus salmoides), signs of the disease may include increased blood flow and darkened skin, distended abdomen, bloated swim bladder, lesions in the membrane lining the body cavity, necrosis (burst cells resulting in inflammation) of gastrointestinal mucosa, pale liver, red spleen, red intestinal caeca, infected gills, lethargic swimming, decreased responsiveness, swimming at the surface and/or in circles, and difficulty remaining upright. Sores or lesions on the outside of the body are secondary and not caused by the actual viral infection (Zilberg et al. 2000; Goldberg 2002; Brunner 2003; Grizzle and Whelan 2004; Beck et al. 2006).

Size: LMBV particles are 130 nm from side to side and 145 nm from corner to corner when they are in the cytoplasm of the host cells. After acquiring an envelope they measure 175 nm in maximum dimension

Native Range: Unknown. However, this virus is very similar to two fish viruses from southeast Asia (Mao et al. 1999; Plumb et al. 1999).

Map Key
This map only depicts Great Lakes introductions.

Great Lakes Nonindigenous Occurrences: LMBV was first detected within the Great Lakes basin in the Bay of Quinte, Lake Ontario in 2000 (Sutherland 2002). That same year, LMBV was detected in Lake George, on the Indiana-Michigan border (Lake Michigan watershed).

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 Ranavirus are found here.

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI200020037Black-Macatawa; Huron; Lake St. Clair; Muskegon; St. Joseph; Tiffin; Tittabawassee
NY200820152Seneca; Upper Genesee
OH200720081Lake Erie
PA201120111Lake Erie

Table last updated 10/1/2023

† 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: LMBV is stable in lab conditions at pH of 3-9. It remains viable in water for at least 3-4 hours, is 10% infective after 2 days, and is still detectable after 7 days (Piaskoski et al. 1999; Scott and Aron 2002; Grizzle and Brunner 2003). LMBV grows best and is most virulent at 30°C, but is able to kill cells in a broad range of temperatures (Grant et al. 2003; Grizzle and Brunner 2003; McClenahen et al. 2005).

LMBV can be passed from one infected fish to another, so any practices that keep infected and uninfected fishes that are in close contact or at high densities can increase transmissions (Grant et al. 2005; Inendino et al. 2005). LMBV can be transmitted through the water and also orally via ingestion of infected animals (Woodland et al. 2002). Transmission from adult to offspring probably does not occur or is very rare (Grizzle and Brunner 2003).

This virus was first known only from wild fish and was not reported from hatcheries until 1999 in the southeastern USA. LMBV can affect Largemouth Bass lethally or subclinically (without symptoms), and is particularly prone to infect bass over 30 cm long. The virus is experimentally pathogenic in Striped Bass (Morone saxatilis) but has never caused fish kills in this species in the wild. LMBV can also subclinically and non-lethally infect Smallmouth Bass (Micropterus dolomieui), Bluegill (Lepomis macrochirus), Crappie (Pomoxis spp.), and Chain Pickerel (Esox niger). Once exposed to LMBV, a population of Largemouth Bass produces antibodies such that subsequent exposures result in less extreme manifestations of the disease. Fish kills can be slow and last for several weeks (Goldberg 2002; Woodland et al. 2002; Grizzle and Brunner 2003; Grizzle et al. 2003; Whelan 2004).

Means of Introduction: Transport of LMBV in North America probably occurs in live wells of fishing boats when infected fish or water are dumped into new habitat or put in contact with uninfected fish, which are then released. Stocking of infected fish could also be a vector.

Status: Established.

Great Lakes Impacts:  

Ranavirus sp. has a high  environmental impact in the Great Lakes.
As Ranavirus sp. has resulted in the reduction of native Largemouth Bass (Micropterus salmoides) populations, this virus is assessed as having a high environmental impact in the Great Lakes. Further research is needed to determine if a developing immunity similar to the populations seen in Florida is realized in Great Lakes Largemouth Bass populations.

In Michigan, LMBV mortality events typically have involved 100-500 fish or 10 percent of the population per lake (Grizzle and Brunner 2003, Whelan 2004). However, Ranavirus sp. has also been implicated in several more significant Largemouth Bass die-offs within the Great Lakes basin, including in Lake George, Indiana, where LMBV was detected in 90% of fish sampled (Grizzle and Brunner 2003, Whelan 2004), and in a small Steuben County, Indiana lake (2011; Sarvay 2012). The latter resulted in the death of 50 percent of the lake’s Largemouth Bass population (Sarvay 2012).

Prevalence of Ranavirus sp. in the state of Michigan was determined using 2000-2003 virus survey data. When detected (15 of 30 surveyed lakes), prevalence at the other lakes ranged from 6.3% (Lake Orion) to 100% (Lake St. Clair, Sanford Lake, Woodland Lake), with detection of the LMBV in close to or more than half of the Largemouth bass sampled from many of these lakes (Whelan 2004). However, levels of fish infection varied among sites and between sample years. For example, the virus was detected in Lake Orion at 6.3% prevalence in 2002 and then at 48% in 2003. In Woodland Lake, Ranavirus sp. was detected at 100% prevalence in 2002 and at 60% in 2003. The virus was also detected in Lake George at 90% prevalence in 2000 and 0% prevalence in 2002 (Whelan 2004). This may suggest the virus enters a water body, infects the population until a peak infection rate is observed, and then prevalence decreases.
Other Great Lakes native species susceptible to infection by Ranavirus sp. include Smallmouth Bass (M. dolomieui), Bluegill (Lepomis macrochirus), Crappie (Pomoxis spp.), and Chain Pickerel (Esox niger). However, mortality events attributed to LMBV are rare in these species (Goldberg 2002, Grizzle and Brunner 2003, Grizzle et al. 2003, Whelan 2004, Woodland et al. 2002).

Ranavirus sp. was implicated in the die-off of over 1,000 and 3,000 Largemouth Bass in South Carolina and a northern Mississippi drainage reservoir, respectively (Bister et al. 2006, Hanson et al. 2001, Plumb et al. 1996). In 2010, LMBV was detected in 40 percent of the Largemouth Bass in Kerr Reservoir and Buggs Lake, Virginia. Since 1995, over 25 fish kills throughout the southeast and Midwestern U.S. have been linked to LMBV (FFWCC 2012).

Initial exposure to LMBV elicits antibody production, resulting in less severe disease manifestation in subsequent exposures (e.g., FFWCC 2012, Goldberg 2002, Grizzle and Brunner 2003, Grizzle et al. 2003, Hodge 2004, Whelan 2004, Woodland et al. 2002). For example, in Florida, Largemouth Bass die-offs associated with LMBV have declined since first detection, and no known die-offs have been observed since 2010 (FFWCC 2012).

Symptoms of LMBV can include lethargy, decreased responsiveness, swimming at the surface and or in circles, and difficulty remaining upright (Beck et al. 2006, Goldberg 2002, Grizzle and Brunner 2003, Zilberg et al. 2000). Because of this altered behavior, infected fish may be more susceptible to predation (Lafferty and Morris 1996). However, cascading food web effects have not been reported as a result of LMBV infection in the Great Lakes.

There is little or no evidence to support that Ranavirus sp. has significant socio-economic impacts in the Great Lakes.
Largemouth Bass sport fishing organizations (e.g., Bass Anglers Sportfishing Society/BASS) have increased spending and time  to evaluate and understand the impacts of LMBV on trophy-sized bass fisheries (Grizzle and Brunner 2003, Neal et al. 2009, Terre et al. 2008, Whelan 2004).

Largemouth bass virus poses no threat to human health (MAF 2008).

There is little or no evidence to support that Ranavirus sp. has significant beneficial effects in the Great Lakes.


Regulations (pertaining to the Great Lakes)

The Great Lakes Fishery Commission lists this species as a restricted pathogen.  Screening is required for centrarchids and esocids. Fish exhibiting clinical signs of disease should not be transferred, stocked or released. When detected in the wild, a surveillance program should be initiated and reasonable means employed to prevent spread to new locations.

Ohio requires out-of-state source facilities of live fish to provide health inspection and testing documentation prior to importation (NCRAC 2010). Michigan requires imported aquacultured fish to be accompanied by either an official interstate health certificate, official interstate certificate of veterinary inspection, or a fish disease inspection report. Importing aquacultured fish from source facilities with a record of an emergency disease within the past two years is prohibited. Fish imported from non-Michigan source facilities and intended for stocking in public waters must be certified free of LMBV (NCRAC 2010). Illinois requires source facilities of any species of live fish, eggs, and sperm to document they are disease free prior to importation (NCRAC 2010). Wisconsin requires source facilities to document fish health inspections prior to importing live fish and eggs (NCRAC 2010).

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.

There are no known physical control methods for this species.

Disinfection of live wells and other contaminated equipment can be accomplished with a 10% household bleach/water solution (i.e., 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).

There is no known cure or effective treatment of LMBV infection (Syska et al. 2012).

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

Remarks: It is possible that LMBV was first introduced to Largemouth bass populations in Florida in 1991 through contact with imported tropical guppies (Poecilia reticulata) or Doctor Fish (Labroides dimidatus). These two species can harbor nearly identical viruses, known as guppy virus (GV6), and doctor fish virus (DFV), respectively. Given that the technology existed much earlier than the 1990s to detect such a virus and that it was being used to detect other fish diseases, it is unlikely that LMBV was present for many years before 1991.

Spread of LMBV has occurred from Florida through adjacent states, and has only recently reached the Great Lakes drainage. This pattern of spread from Florida could either be due to increased detection efforts in states adjacent to places where recent outbreaks occurred, or to an actual radial spread of the disease. There are a few different strains of this virus present in North America, which suggests either multiple introductions to the continent or that LMBV is not exotic to the continent. More studies need to be carried out to clarify where the virus originated (Mao et al. 1999; Plumb et al. 1999; Goldberg 2002; Grizzle et al. 2002; Goldberg et al. 2003; Grizzle and Brunner 2003).

References (click for full reference list)

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

Contributing Agencies:

Revision Date: 8/17/2018

Citation for this information:
Kipp, R.M., A.K.Bogdanoff, A. Fusaro, and R. Sturtevant., 2023, Ranavirus: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=2657, Revision Date: 8/17/2018, Access Date: 10/2/2023

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.