Spring Viremia of Carp

Barbara D. Petty, Allen C. Riggs, RuthEllen Klinger, Roy P.E. Yanong and Ruth Francis-Floyd2Introduction
Spring viremia of carp (SVC) is a viral disease that can cause significant mortality of common carp (Cyprinus carpio). This species is raised as a food fish in many countries and has also been selectively bred for the ornamental fish industry, where it is known as koi. Historically, the disease has been a problem in Europe, the Middle East, and Russia. Recently, SVC has been reported in koi in the United States for the first time. This information sheet is intended to inform veterinarians, biologists, culturists, and hobbyists about SVC.What is Spring Viremia of Carp?

Spring viremia of carp is caused by Rhabdovirus carpio, a bullet-shaped RNA virus. The disease has been reported in common carp (or koi) (Cyprinus carpio), grass carp (Ctenopharyngodon idella), bighead carp (Aristichthys nobilis), silver carp (Hypophthalmichthys molitrix), and Crucian carp (Carassius carassius), a close relative of the goldfish. Recent evidence suggests that common goldfish (C. auratus) are also susceptible.

The disease was initially diagnosed in Yugoslavia (Fijan et al. 1971). Since then, it has been identified in other European countries, Russia, and the Middle East. Mortality has reached 70% in yearling carp from European populations. Adult fish can also be affected but to a lesser degree.What are the Signs of SVC?

Clinical signs of SVC are often non-specific and may include darkening of the skin, exophthalmia (pop-eye), ascites (dropsy), pale gills, hemorrhages in the gills, skin, and eye, and a protruding vent with a thick mucoid (white to yellowish) fecal cast.

Internally, edema (fluid build up in organs and in the body cavity), inflammation, and pinpoint hemorrhages in many organs, including the swim bladder, may be present.

The presence of pinpoint hemorrhages in the swim bladder is considered an important indicator of this disease. The intestine is often severely inflamed and may contain significant amounts of mucus. The spleen is often enlarged.

Concurrent infection with bacteria, particularly Aeromonas (A. salmonicida or A. hydrophila), may confuse the diagnosis as fish will show signs of systemic infection such as ascites and hemorrhages.
Behaviorally, infected fish may appear lethargic, exhibit decreased respiration rate, and loss of equilibrium. Moribund fish have been reported to lie on their sides, often on the bottom of the tank, and when startled swim up but then return to the bottom. Fish are also reported to congregate where there is slow water flow and near pond banks (Fijan 1999).

Transmission of SVC
The rhabdovirus that causes SVC enters the fish through the gills, replicating in gill epithelium (Ahne 1978; Baudouy et al. 1980). The virus is spread via feces in the mucoid casts. Blood-sucking parasites, including leeches and the fish louse Argulus, have been implicated in spreading the disease (Pfeil-Putzien 1977; Ahne 1985). Mechanical transmission by birds and equipment is suspected because of the longevity of the virus in water, mud, or following dessication (Ahne 1982a; Ahne 1982b).

Experimental transmission has been accomplished by co-habitation, intracranial and intraperitoneal injection, intubation of the virus into the intestine, and by immersion. However, direct application of the virus to scarified skin has been unsuccessful. (Fijan 1972; Fijan et al. 1971; Hill 1977).

The presence of virus in ovarian fluids suggests that vertical transmission (female parent to offspring) may be possible (Fijan 1999).

Effect of Water Temperature
Although other factors, such as age, can determine how severely the disease will affect a population, the temperature at which fish become infected, temperature fluctuations during the infective period, and the ability of the fish to mount a timely immune response seem to be the most important components for SVC.

In natural outbreaks, mortalities were confirmed in spring of 1969 and 1970 in Yugoslavia when water temperatures ranged from 12°C to 22°C (54°F to 72°F).The optimum temperature for viral replication in vitro is 20-22°C (68-72°F), however, this is also an optimum temperature range for immune function of susceptible species (Fijan 1999). Clinical and experimental data indicate that maximum mortality can be expected at water temperatures below 18°C (64°F) (Fijan 1999; McAllister 1993).

These findings have led experts (Wolf 1988; Ahne 1980; Fijan 1999) to suggest that outbreaks of SVC can be prevented or stopped in mature fish by raising water temperatures above 20°C (68°F); however, the results of such attempts have not been well documented. Because of the potential severity of the disease, depopulation is recommended.How is SVC diagnosed?

Diagnosis of SVC can be accomplished by several methods. Direct methods include virus isolation and identification using fathead minnow (FHM), epithelioma papillosum of carp (EPC), and primary carp ovary cells (COC) cell lines. Indirect tests for SVC include ELISA, virus neutralization and immunofluorescence of suspect tissue.

Laboratories approved by the USDA to test fish for SVC are listed in Appendix A.

How is SVC treated?
Antiviral drugs are not available to treat SVC or other viral diseases of cultured fish. Temperature manipulation is probably the most practical means of preventing or controlling mortality once an epizootic is in progress. Maintaining water temperature above 20°C (68°F) may prevent a potential outbreak.

In active outbreaks, efforts are directed at depopulating infected stock, and disinfecting all areas where infected fish were held. However, in some circumstances, this may be difficult. The virus can be infective in mud and water for up to 42 days (Plumb 1999).

The virus can be inactivated by formalin, ozone, sodium hypochlorite (chlorine at 500 ppm for ten minutes), organic iodophors, gamma and ultraviolet irradiation, pH extremes of < 4.0 or greater than 10.0, and heating at 60°C (140°F) for 15 minutes (Smail and Munro 1989; Fijan 1999). All equipment and tanks, raceways, and ponds should be disinfected.

Fish that are exposed to physiological stressors such as crowding, handling, poor water quality, malnutrition, and sudden temperature changes are most susceptible, because of resulting immune system suppression.

Vaccine development has been attempted in the Czech Republic (Macura et al. 1983) with promising results but further studies are necessary. The development of genetically resistant strains should also be pursued (Fijan 1999).

How can SVC be prevented?
In the face of infection, maintaining a water temperature of 20°C (68°F) or higher will increase the chances for infected fish to develop an immunity to SVC, reducing mortalities. It is unknown at this time whether fish that have been exposed to SVC, and subsequently become immune, will serve as a source of virus to unexposed fish.

Few fish should be purchased from SVC-free suppliers and farms.Regulatory Considerations
Spring viremia of carp is listed as a notifiable disease, by the Office International des Epizooties (OIE), in the International Aquatic Animal Health Code (OIE 1997a). The OIE has published a diagnostic manual that includes protocols required to confirm a diagnosis of SVC (OIE 1997b). It also lists criteria for "SVC-free" status for aquaculture facilities and geographic regions.

In the United States, suspect cases should be sent to one of the three USDA-approved labs listed in Appendix A for confirmation. SVC is considered a notifiable disease in the United States, therefore prompt notification of the State Veterinarian's office and appropriate USDA-APHIS Veterinary Services officials is mandatory.

References and Recommended Reading
Ahne, W. 1978. Uptake and multiplication of spring viremia of carp virus in carp, Cyprinus carpio, L. Journal of Fish Diseases 1:265-268
Ahne, W. 1980. Rhabdovirus carpio - Infektion beim karpfen (Cyprinus carpio): Untersuchungen über reaktionen des wirtsorganismus. Fortschritte in der Veterinärmedizin 30:180-183.
Ahne, W. 1982a. Vergleichende untersuchungen über die stabilität von vier fischpathogenen viren (VHSV, PFR, SVCV, IPNV). Zentralblatt fur Veterinärmedizin (B)29:457-476.
Ahne, W. 1982b. Untersuchungen zur tenazität der fischviren. Fortschritte in der Veterinärmedizin 35:305-309.
Ahne, W. 1985. Argulus foliaceus L. and Philometra geometra L. as mechanical vectors of spring viremia of carp virus (SVCV). Journal of Fish Diseases 8:241-242.
Baudouy, A.M., Danton, M. and Merle, G. 1980. Virémie printanière de la carpe: résultants de contaminations expérimentales effectuées au printemps. Annales de Recherches Veterinaires 11:245-249.
Fijan, N. 1972. Infectious dropsy in carp: a disease complex. Symposium of the Zoological Society of London 30:39-51.
Fijan, N. 1999. Spring viremia of carp and other diseases and agents of warm-water fish. In: Woo, P.T.K. and Bruno, D.W. (eds.), Fish Diseases and Disorders, Volume 3, Viral, Bacterial and Fungal Infections, CABI Publishing, Oxon, UK, pp 177-244.
Fijan, N., Petrinec, Z., Sulimanovic, D., Zwillenberg, L. 1971. Isolation of the viral causative agent from the acute form of infectious dropsy of carp, Veterinarski Arhiv 41:125-138.
Hill, B. 1977. Studies of spring viremia of carp virulence and immunization. Bulletin de L'Office International des Epizooties 87:455-456.
McAllister, P.E., 1993, Goldfish, koi, and carp viruses. In: Stoskopf, M.K. (ed). Fish Medicine, W.B. Saunders Company, Philadelphia, PA, pp 478-486.
Macura, B., Tesarcik, J., and Rehulka, J. 1983. Survey of methods of specific immunoprophylaxis of carp spring viremia in Czechoslovakia. Práce VÚRH (Vyzkumny ústav rybársky a hydrobiologicky) Vodnany (English = Papers of RIFH [Research Institute of Fishery and Hydrobiology] Vodnany) 12:50-56.
Office International des Epizooties. 1997a. International Aquatic Animal Health Code, Second edition. Office International des Epizootis, Paris, France. 192 pp.
Office International des Epizooties. 1997b. Diagnostic Manual for Aquatic Animal Diseases, Second edition. Office International des Epizooties, Paris, France. 251 pp.
Pfeil-Putzien, C. 1977. New results in the diagnosis of spring viremia of carp caused by experimental transmission of Rhabdovirus carpio with carp louse (Argulus foliaceus). Bulletin de L'Office International des Epizooties 87:457.
Plumb, J.A. 1999. Health maintainence and principal microbial diseases of cultured fish. Iowa State University Press, Ames, IA, pp 77-90.
Smail, D.M. and Munro, L.S. 1989. The virology of teleosts. In: Roberts, R.J. (ed), Fish Pathology, Second edition. Balliere-Tindall, London, UK, pp 173-241.
Wolf, K. 1988. Fish viruses and fish viral diseases. Cornell University Press, Ithaca, NY, pp 191-216.

Appendix A
USDA approved diagnostic laboratories capable of testing for Spring Viremia of Carp
1. University of Arkansas-Pine Bluff
Cooperative Extension Program
PO Box 4912 OR 1200 University Drive
Pine Bluff, AR 71611
Phone: (870) 543-85372.

Pennsylvania Animal Diagnostic Laboratory System
State Veterinary Laboratory
2305 North Cameron Street
Harrisburg, PA 17110
Phone: (717) 787-88083.

Washington Animal Disease Diagnostic Laboratory
College of Veterinary Medicine
Washington State University
PO Box 647034
Pullman, WA 99164-7034
Phone: (509) 335-9696
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Footnotes
1. This document is Fact Sheet VM-142, one of a series from the Department of Fisheries and Aquatic Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published: July 2002. Please visit the EDIS Web Site at http://edis.ifas.ufl.edu.
2. Barbara D. Petty, Aquaculture Verterinarian, Bureau of Veterinary Diagnostic Laboratories, Division of Animal Industry, Florida Department of Agriculture and Consumer Services, 2700 N John Young Parkway, Kissimmee, FL 34741.
Allen C. Riggs, Lecturer, RuthEllen Klinger, Biological Scientist, and Ruth Frnacis-Floyd, Professor, Department of Large Animal Clinical Sciences (College of Veterinary Medicine) and Department of Fisheries and Aquatic Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Gainesville, 32611.
Roy P.E. Yanong, Assistant Professor, Tropical Aquaculture Laboratory, Department of Fisheries and Aquatic Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Ruskin, FL 33570-3434.
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Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Christine Taylor Waddill, Dean
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Summary:

The first identification of spring viraemia of carp (SVC) in the US has been made in a koi hatchery in Kernersville, North Carolina. SVC is a disease of several species of cyprinid fishes caused by Rhabdovirus carpio.

Cyprinid fishes are produced as food fish, ornamental fish (koi and goldfish) and baitfish.  In 1998 in the US, 59 facilities produced food carp, 115 produced koi, 65 produced ornamental goldfish, and 34 produced feeder goldfish.  The total value of farm sales was $21.2 million.  The US exported  $1.8 million worth of live carp in 2001, almost exclusively to Canada.

In response to the US SVC finding, all fish in the affected ponds have been slaughtered and the affected ponds have been drained.  A surveillance program has been instituted and the hatchery has been placed under quarantine.  The North Carolina Wildlife Commission has been contacted to test rivers and tributaries that receive effluent water from the hatchery.  Several of the susceptible species have been reported in the wild in waters of west-central North Carolina.

How extensive is the situation?

The first identification of spring viraemia of carp (SVC) in the US has been made in a koi hatchery in Kernersville, North Carolina.  Koi are a colored, ornamental strain of the common carp, Cyprinus carpio.  SVC was first suspected in April 2002, when the hatchery experienced a 10% per week death rate in juvenile koi, which were being observed as part of a quality control program.  Diagnostic samples were first sent to the University of Arkansas Pine Bluff Laboratory, an APHIS approved diagnostic laboratory, then forwarded to the OIE reference laboratory located in Weymouth, United Kingdom, where the diagnosis was confirmed on July 5, 2002 .  The premises where infected fish were found consisted of 202 ponds divided among 6 locations.  Infected fish were detected in a total of 4 ponds.  Of 150,000 koi in the 4 ponds, 15,000 died and the remaining 135,000 were depopulated.  The 4 affected ponds were drained.

The hatchery is no longer experiencing signs of SVC in any of the other ponds or processing facilities.  A foreign animal disease investigation is underway, but the potential source of infection has not been identified.  Samples from all remaining ponds are being sent to theUniversity of Arkansas Pine Bluff Laboratory. Tanks and equipment have been disinfected. A surveillance program has been instituted and the hatchery has been placed under quarantine.  The North Carolina Wildlife Commission has been contacted to test rivers and tributaries that receive effluent water from the hatchery.

What Species are Susceptible to Spring Viraemia of Carp virus?

According to the OIE, susceptible host species of Spring Viraemia of Carp virus (SVCv) include cyprinid fishes, specifically the common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molotrix), bighead carp (Aristichthys nobilis), crucian carp (Carassius carassius), goldfish (Carassius auratus), tench (Tinca tinca), and sheatfish (Silurus glanis).  SVC is an OIE List B disease.  SVC has previously been reported in western and eastern Europe and Israel .

What is Spring Viraemia of Carp?

Spring Viraemia of Carp is systemic, acute and highly contagious.  SVC is caused by Rhabdovirus carpio, which is a typical bullet shaped virion about 60-90 nm wide and 90-180 nm long and which bears a regular surface array of glycoprotein spicules.  The virus adsorbs to cellular plasma membranes and enters the cell by receptor-mediated endocytosis.  The gill is the most common portal of entry.  Infected cells develop cytoplasmic inclusion bodies and mature virions are released by budding from the plasma membrane.  SVC is transmitted horizontally and by blood sucking parasites such as the carp louse (Argulus foliaceus) and leech (Pisciola geometra).  SVC typically occurs when water temperatures are less than 18°C and is most common in the spring.  At 20-22°C, infection occurs but clinical disease does not develop.  When clinical disease is present, mortality ranges from 30 to 70%.  Affected fish often seek slow moving water or lie on the bottom.  As the disease progresses, fish become non responsive to external stimuli, sluggish, swim on their side and rest in abnormal positions.  The skin becomes darkened and the belly swollen.  Petechial and ecchymotic hemorrhages and exopthalmos are common and reflect viral predilection for endothelium, resulting vascular leakage and loss of fluid balance.  Long, thick, mucoid casts may be observed from the vent.  Successful treatment of infected fish has not been demonstrated.  There is no approved vaccine for SVC in the US. Control measures include iodophore disinfection of eggs and periodic chemical and physical disinfection of ponds and equipment.  Minimizing stress and overcrowding and sanitary disposal of dead fish are also recommended.  Raising fish at a water temperature of 19-20° C has been suggested, but the cost of heating water in a temperate climate can be prohibitive.

Source: OIE Disease Information Report, Spring Viraemia of Carp and other Viral Diseases and Agents of Warm Water Fish by N. Fijan, USDA Area Veterinary Office in North Carolina .

What is the size of the carp/koi and the goldfish industries in the US and in North Carolina?

In 1998, the US had 39 facilities that produced carp as a food fish, with a total sales value of $1.3 million (Table 1).  North Carolina had only 1 facility that produced stocker carp intended to be raised as food fish. 

A total of 115 facilities produced koi in the US in 1998. The total sales value of these facilities was $3.9 million.  Ornamental goldfish were produced in 65 facilities, with sales totaling $6.7 million.  North Carolina had 6 facilities that produced koi, with a sales value of $137,000, and 3 facilities that produced ornamental goldfish, with undisclosed sales value.

Goldfish are also used as baitfish.  Thirty-four (34) facilities produced feeder goldfish in the US in 1998, with sales totaling $9.3 million.  North Carolina had 2 facilities that produced feeder goldfish. 

Table 1:  Number of facilities and value of sales for affected fish in the US and North Carolina, 1998

- = withheld to avoid disclosing data for individual farms

Source:  USDA, NASS, 1998 Census of Aquaculture

What is the USA’s place in the international market for affected fish?

The US produced 11,739 metric tons of carps, barbels, and other cyprinids in 1999, accounting for less than 0.1% of world production.

Source: United Nations FAO

What are the U.S. exports of affected fish?

The US exported live carp worth $1.8 million and $738,000 in 2001 and January through April 2002, respectively.  These fish were exported almost exclusively to Canada, with only a minor sales value to Mexico in 2001.  None of the live carp that were exported in 2002 or 2001 originated in North Carolina.[1]  Goldfish export data are not available.

Table 2:  US exports of live carp, 2001 and January-April 2002

Source: World Trade Atlas

Are susceptible species found in the wild in west-central North Carolina?

In 2000, a review of the diversity and distribution of native freshwater fish of the southern United States, including those of  the Pee Dee River basin, was published.  Of the 662 native freshwater and diadromous fishes and 24 marine fishes listed, none were of the same genus as those listed as susceptible by the OIE to spring viraemia of carp.

Non-native susceptible fish have been detected in the waters of west-central North Carolina including the grass carp, common carp, goldfish, and tench.  The overall size of the population of these non-native species within North Carolina is unknown.

Sources: USGS @ nas.er.usgs.gov/fishes/accounts, July 17, 2002;

Diversity, Distribution, and Conservation Status of the Native Freshwater Fishes of the Southern United States.  Published in Fisheries, October 2000.

CEI’s plans for follow up:

CEI will continue to monitor the situation but has no plans at this time to issue additional reports.  If you seek more information or wish to comment on this worksheet, please reply to this message or contact Robert Harris at (970) 494-7327 or Christine Kopral at (970) 494-7325.

On the SFBAKC web site (http://www.sfbakc.org/articles/svc.html#doc) you have an old essay from Eric Johnson about SVCV. That essay was written soon after the Blue Ridge disaster. It is out of date, inaccurate, and will confuse folks visiting your web site. The essay trivializes what should be regarded as a huge threat to koi. SVCV is on the OIE list of reportable diseases because it is a highly infectious and devastating disease, not because of international politics. Visitors to your site would be much better served by accurate information about this nasty disease. In addition, the essay continues to link the SVCV virus and the Blue Ridge name. Let's give them a chance to move on!

Regards,

Andrew E. Goodwin, Ph.D.
Professor/Associate Director
Fish Pathologist/Inspector (AFS-FHS)
Aquaculture/Fisheries Center
University of Arkansas at Pine Bluff
1200 N. University Drive
Mail Slot 4912
Pine Bluff, AR 71601

Phone 1-870-575-8137
FAX 1-870-575-4638
Mobile 1-870-540-7811
email agoodwin@uaex.edu