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Spring viremia of carp (SVC) is a viral disease that can cause significant mortality in several carp species including the common carp (Cyprinus carpio). These species are raised as a food fish in many countries and koi carp have been selectively bred for the ornamental fish industry. Historically the disease has been a problem in Europe, the Middle East, and Russia, but was reported in koi and feral carp in the United States for the first time in 2002. Listed as a notifiable disease by the World Organization for Animal Health (OIE), diagnosis of SVC in farm raised fish in the US may result in quarantine of the infected fish and depopulation. 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 an infection caused by Rhabdovirus carpio, a bullet-
Where Is It Found?
Thought to be present in Europe for decades, spring viremia of carp virus (SVCv) was initially diagnosed in Yugoslavia (Fijan et al. 1971). Since then, it has been identified in other European countries, Russia, Brazil, the Middle East, China, and North America.
In the US, SVC has been diagnosed both in farmed koi and feral common carp. In 2002, it was diagnosed in farmed koi in North Carolina and in feral carp in Wisconsin. It is important to note there was no connection between the two cases. It was also diagnosed in farmed koi in Washington and Missouri in 2004 and in feral common carp in the Mississippi River in Minnesota in 2007. The most recent SVC finding was in 2011 in feral carp in Minnesota waters. SVC is not believed to be widespread in the US but rather limited to certain areas in wild susceptible populations. For purposes of disease regulation, USDA considers spring viremia of carp a foreign animal disease in the United States.
What Are The Signs Of SVC?
Clinical signs of infection with SVCv are often non-
Other clinical signs may include darkening of the skin; exophthalmia (pop-
Figure 1; Koi infected with SVCv. Note hemorrhages on body wall.
Transmission Of SVCv;
The rhabdovirus that causes SVC enters the fish through the gills, replicating in gill epithelium and spreading to internal organs (Ahne 1978; Baudouy et al. 1980). The virus is distributed to other susceptible fish via mucoid casts in feces from infected fish. Blood-
Experimental transmission has been accomplished by co-
The presence of virus in ovarian fluids suggests that vertical transmission (from female parent to offspring) may be possible (Fijan 1999), but there is no evidence this has occurred.
Fish that survive an outbreak of SVCv may develop immunity to the virus. However, they can shed virus and thus serve as a source of virus to unexposed fish. Fish exposed to virus should be considered to be carriers. The length of time carrier fish can shed virus is unknown.
Factors That Influence Disease;
Young fish are more susceptible to infection with SVCv; mortality can reach 70% in yearling carp (Plumb 1999; OIE 2015a). Adult fish can also be affected, but usually to a lesser degree.
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 to 22°C (68 to 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 between 10 to 18°C (50 to 64°F) (Fijan 1999; McAllister 1993).
Fish that are exposed to physiological stressors such as crowding, handling, poor water quality, malnutrition, and sudden temperature changes are more susceptible because of resulting immune system suppression.
How Is SVCv Diagnosed?
Diagnosis of SVCv can be accomplished by several methods. A direct method is to isolate the virus using fathead minnow (FHM) or epithelioma papillosum of carp (EPC) cell lines. If the virus is present, it will cause the cells to degenerate and round (see Figure 2). To confirm that SVCv is in the cell line, one or more of indirect test methods should be performed by a federally approved laboratory. Indirect methods for SVCv diagnosis include enzyme-
Suspect cases of SVC in the US can be sent to any lab that can test for the disease; however, samples collected for the purpose of meeting export requirements must be sent to a USDA-
If a sample tests positive for the virus, it should be submitted to the National Veterinary Services Laboratory (NVSL) in Ames, Iowa—https://www.aphis.usda.gov/animal_health/lab_info_services/downloads/ContactByDisease.pdf.
A catalog of services and fees and other information regarding NVSL is available here:
Photomicrograph of cell culture (epithelioma papillosum of carp) that is infected with SVCv. Black arrow points to cells that appear normal, white arrow to cells dying from SVCv.
How Are SVC Outbreaks Managed?
Antiviral drugs are not available to treat SVC or other viral diseases of cultured fish. Due to the potential severity of the disease and regulatory concerns, depopulation is recommended.
In active outbreaks, efforts are directed at containing and/or quarantining infected and exposed 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). It can also survive in water without a host for 5 weeks at 10°C (50°F) (OIE 2015a). The fate of the infected and exposed fish will likely be determined by state or federal authorities.
Though the virus is hardy, it can be inactivated by a number of methods. Appendix A lists chemical concentrations and application times to achieve inactivation of the virus. All equipment and tanks, raceways, and ponds should be disinfected. Ponds that have housed infected fish should be fallowed (left un stocked) for a period of time to be determined with regulatory advisory. Re-
The development of genetically resistant strains has been recommended (Fijan 1999), but not pursued (Brown and Bruno 2002). Vaccine development has been attempted in the Czech Republic (Macura et al. 1983) with promising results. One group in the US developed a DNA vaccine for SVCv that was efficacious in laboratory trials (Emmenegger and Kurath 2008). To date, there is no legal vaccine for SVCv in the US.
How Can SVCv Infections Be Prevented?
Bio security measures should be followed especially when working with SVCv-
Spring viremia of carp is listed as a notifiable disease by the OIE in the International Aquatic Animal Health Code (OIE 2015b). It is also a notifiable disease in the United States. See;
Prompt notification of the state veterinarian's office and appropriate USDA-
Appendix A; Methods to inactivate SVCv (Smail and Munro 1989; Fijan 1999; OIE 2015a)