Viral Hemorrhagic Septicemia Virus (VHSV) was identified in the freshwater environment of North America for the first time in 2005. The virus was found in two separate instances: in muskellunge from Lake St. Clair, Michigan by researchers at Michigan State University and in freshwater drum from the Bay of Quinte, on the Canadian shore of Lake Ontario by researchers from the University of Guelph in Ontario, Canada.
VHSV was first found in New York State in round gobies collected during a mortality event in the St. Lawrence River. The fish were submitted by the NYS DEC to the Aquatic Animal Health Program at Cornell University in May, 2006. Since that time the Aquatic Animal Health Program has had confirmed cases of VHSV in muskellunge, burbot and round gobies from the St. Lawrence River and round gobies and smallmouth bass from Lake Ontario. During surveillance efforts in 2006, VHSV has been confirmed in bluntnose minnows from the St. Lawrence River and emerald shiners from the Niagara River and Lake Erie.
Where has VHSV been found and confirmed in New York:
The Great Lakes proper:
St. Lawrence River
Inland water bodies:
Seneca-Cayuga Canal (Seneca County)
Little Salmon River (near Mexico, NY)
Private Pond (Niagara County)
Where else has VHSV been found and confirmed in the Great Lakes Basin:
The Great Lakes proper:
Bay of Quinte, north shore of Lake Ontario (Canada)
Lake St. Clair
Inland water bodies:
Winnebago chain of lakes (Wisconsin)
Budd Lake (Michigan)
Clear Fork Reservoir (Ohio)
Baseline Lake (Michigan)
List of Fish Species Regulated by the VHSV Interim Rule (list
Effective 9 September 2008).
Muskellunge (57", 45 lbs.) from the St. Lawrence River, NY.
Some FAQ's on VHSV
What is VHSV?
VHSV is a Rhabdovirus. There are other known fish rhabdoviruses (Infectious Hematopoietic Necrosis Virus, Spring Viremia of Carp Virus), but the most well known member of the Rhabdovirus family is the rabies virus. It is important to note here that VHSV does not infect humans. As a Rhabdovirus, VHSV is an RNA virus that has an envelope. Viruses, in general, must reside in a living cell and can survive outside of a living cell for a relatively short time. Historically, VHSV has been known in Europe as the most serious viral disease of rainbow trout reared in freshwater. More recently, information suggests that VHSV may have actually been a disease of a variety of saltwater fish species and gained access to the freshwater environment in Europe when it was common for unpasteurized fish caught in the marine environment to be used to feed rainbow trout. In 1988 and 1989 VHSV was found in apparently healthy returning Chinook and coho salmon in the Puget Sound area of Washington state. Those isolations constituted the first documentation of VHSV in the Western Hemisphere. Since 1988, VHSV has been isolated from a variety of marine fish species on both the Pacific and Atlantic coasts of North America. The identification of VHSV in 2005 in fish from Lake St. Claire, Michigan and in fish from the Bay of Quinte, Lake Ontario, Canada were the first documentations of VHSV in the freshwater environment of North America.
What methods are used to detect VHSV?
Procedures used to detect VHSV require that a laboratory be appropriately equipped to work with fish viruses. Presence of the virus cannot be determined without rather sophisticated laboratory testing. The specific methods used to detect VHSV are provided in two resources: the OIE (World Animal Health Association) Manual and the Fish Health Section/American Fisheries Society document titled "Suggested Procedures for the Detection and Identification of Certain Finfish and Shellfish Pathogens." There is a two step procedure used to detect the virus: (1) The virus is first isolated in a cell culture. In this procedure the cell culture is examined for destruction of the cells, called cytopathic effects or CPE. Since there are several different viruses that may cause CPE, the specific identity of the virus must then be determined. (2) The specific identity of the virus is determined by either the use of a specific antibody against the virus or by some kind of molecular technique where a specific portion of the genetic structure of the virus is detected. In the former case a test called a serum neutralization is performed and in the latter case a Polymerase Chain Reaction (PCR), or in the case of VHSV as an RNA virus, an RT-PCR is performed. Our Aquatic Animal Health Program at Cornell is developing a Quantitative RT-PCR (qRT-PCR) for VHSV. Our use of the qRT-PCR to date has shown that it is far more capable of detecting the virus when it is present in low quantities. The test also lends itself to the processing of large quantities of samples. Once developed, the qRT-PCR will go through a process called "validation," where it will be compared against the current accepted testing methodologies (OIE Manual and Fish Health Section Blue Book) for sensitivity and specificity with the goal of having the qRT-PCR listed in the above two documents as an accepted testing method.
What are the most common ways for fish to become infected with the virus?
This is a major research question. We consider the following as potential methods by which the virus could be transmitted: an infected fish shedding virus into the water to infect an non-infected fish, a predatory fish eating a prey species of fish that is infected, infected brood fish that shed the virus with the reproductive products to result in infected young fish, movement of virus in water that is used to transport infected fish, contamination of fish handling equipment (nets, buckets, hauling tanks, etc.) with virus, movement of virus by animals other than fish (amphibians, reptiles, birds, small mammals). There may be other means of movement of the virus that will result in infecting fish.
Will fish develop an immunity to VHSV?
As with any fish diseases, it is extremely important to remember that fish are cold-blooded animals as opposed to warm-blooded animals that have a constant body temperature (ie. humans). The impact of water temperature is always important in fish diseases. Because fish are cold-blooded, virtually all of their physiological processes and how effectively they function are linked to water temperature. Of particular importance when it comes to issues of fish disease, is the impact water temperature has on the immune system of fish. As with all animals, the immune system of provides a fish with its disease fighting capabilities. Cold water fish, such as rainbow trout may perform best at 15C, while a warm water fish, such as a channel catfish will grow best at a much warmer water temperature near 25C. If you place either of these fish at a temperature that is not optimum for that species, they will not perform as well. But there is an additional complication; that of a changing water temperature. We often hear the phrase: "Change Is Good." But if you are a fish, change is NOT good. A fish will acclimate to a specific water temperature. If that water temperature changes, the fish must acclimate again. This can be stressful to the fish. In the broad scheme of things, this is why the spring and fall seem to be the times of the year when we see the most fish diseases in nature and in fish culture where fish are raised outdoors in ponds or raceways (indoor fish culture systems with a constant temperature are a very different matter). One more complication is spawning. Fish that are spring spawners or fall spawners have that stressful activity as an additional factor to deal with.
Now, let's look at the pathogen. Some pathogens have a water temperature where they are more problematic (more virulent = their ability to infect and cause disease is greater). Therefore, it is necessary to think of water temperature in terms of its impact on the immune system of the fish and on the pathogen. Just how much impact the water temperature will have on the ability of a pathogen to infect a fish or the ability of a fish to defend itself from the pathogen with a functioning immune system depends a lot on the species of fish, the characteristics and quantity (infectious dose) of pathogen present and all the various environmental stressors that the fish is exposed to at the time. It is a very complicated dynamic that occurs and there really aren't any simple answers.
Is there anything wrong with moving fish/minnows/equipment within areas that are already affected?
In general it is not advisable to move fish that are known to be infected to a new location whether that new location is disease free or that new location contains infected fish. In the case of VHSV this should not be done until we know a lot more about this virus as well as such things as the dynamics of how this virus can survive in the environment and what constitutes an infectious dose under different conditions. There is some scientific literature that has demonstrated that by only stocking fish that are disease free into a body of water in which a disease is present, it may be possible to dilute that disease out of the population. This work was done as a field study with the Infectious Pancreatic Necrosis Virus (IPNV) in salmonids. While IPNV is a very different virus from VHSV, the findings of the IPNV study may provide a valuable management strategy to limit the impact of VHSV in the Great Lakes.
VHSV Articles in the Cornell Chronicle:
18 March 2013
USDA APHIS Emerging Disease Notice (July 2006)
USDA APHIS Industry Alert (August 2006)
USDA APHIS Questions and Answers about the VHSV Federal Order (November 2006)
Fish Species Affected by the VHSV Federal Order (effective 8 November 2007)