Risk Analysis on Spring Viraemia of Carp from Imported Cyprinidae

Spring Viraemia of Carp (SVC), also known as catfish infectious ascites, is an acute, hemorrhagic infectious septicaemia. The disease can harm salmon, catfish, Carassius auratus, Hypophthalmichthys molitrix, Aristichthys nobilis, etc., and is popular in both Europe and Asia. SVC is the first type of quarantine target for fish port quarantine. The World Organization for Animal Health (OIE) lists SVC as a disease that needs to be declared, and China’s Ministry of Agriculture defines it as a class of animal disease. In order to avoid the risk of introduction of IHN due to the introduction of fingerlings, and provide decision-making departments with scientific decision-making data, this paper conducts a systematic risk analysis of SVC from risk assessment, risk management, and risk communication.


Pathogens
Spring viraemia of carp virus (SVCV), also known as rheumatoid virus, is tentatively listed by the International Viral Classification Commission in its seventh report in 2000 as a provisional membership of Rhabdoviridae and Vesiculovirus genus [1]. The Rhabdoviridae family is divided into 3 genera: Lyssavirus, vesicular virus genus, and plant rhabdovirus group. There are currently five rhabdoviruses that cause important fish diseases. The RNA and protein composition are basically similar to mammalian rhabdoviruses. Among them, protein profiles of members of Hunchun virus and pikefry rhabdovirus (PFRV) and vesicular stomatitis virus are similar. It is classified as a tentative member of the vesicular stomatitis virus genus; viral hemorrhagic septicemia virus (VHSV), infectious hematopoietic necrosis virus (IHNV) and salmon rhabdovirus. Under electron microscope, SVCV exhibits a typical elastic shape of vertebrate rhabdoviruses. The virus particles are approximately 80 -180 nm in length, approximately 60 -90 nm in diameter, and have a spiral symmetric core shell with a diameter of approximately 50 nm body. The genome of the virus is a linear, single-stranded, negative-stranded RNA with no segments. The buoyant density of SVCV in lanthanum chloride is 1.195 to 1.200 g/mL. At pH 3 and 12, fat solvent and heat (56˚C) can destroy the infectivity of virus particles, 3% formalin, 0.01% organic iodine, 2% NaOH, and UV (254 nm) can inactivate virus. Repeated freeze-thaw can destroy the partial activity of the virus. Adding 2% to 10% of bovine serum during lyophilization can protect its activity. The SVCV viral genome is a linear single-stranded negative-stranded RNA with a sedimentation coefficient of 38 to 40 s in a sucrose gradient of 5% to 20%. The SVCV genomic RNA is about 11,019 bp in length and contains five open reading frames (ORFs) encoding the five major structural proteins of SVCV. From the 3' to 5' ends of the genomic RNA, they are nucleoproteins in turn: (N), phosphoprotein (P), matrix protein (M), glycoprotein (G) and RNA polymerase (L). In 1984, Kiuchi and some other people first studied the characteristics of the SVCV viral genome and published the M protein gene sequence and a base sequence that is located at the 3' end of the genomic RNA and is approximately 70 bp in length. conditions. In addition to carps, SVCV also infects non-carpodidae such as silurus glanis, rainbow trout (Oncorhynchus mykiss), and white pekin (Esox lucius).
In laboratory infection conditions, there are other carp species that are sensitive to SVCV, including Rutilusrutilus and Danio rerio, and it can be concluded that other species of carp are also susceptible to SVCV. Some species are susceptible to experimental conditions. For example, Lebistes reticulatus, Lepomis gibbosus [3]. However, hybrids are not sensitive to SVCV. SVCV can infect salmon of all ages, younger fish being more susceptible.  [4]. SVCV-infected salmon can excrete viruses via feces and urine, and viruses that are excreted in vitro can maintain infection activity in water for more than 4 weeks, and can maintain infection activity in mud at 4˚C to 10˚C for more than 6 weeks. In addition, equipment contaminated with SVCV can also be a source of infection. In summary, SVCV is mainly horizontal and vertical transmission is not the main route of SVCV infection. In addition to the direct relationship between water temperature and the outbreak of SVC, it is related to the age, stocking density, and environmental conditions of carp. After catching SVCV, the carp tends to accumulate at the water inlet. The parade and the response to sensory stimulation are slow, and the respiratory intensity is weakened. Before the death, the symptoms are depression, rest and body tilt.

Initial Diagnosis
The dying squid infected with SVCV has obvious clinical symptoms, such as skin bleeding, pale sputum and ascites. Changes in necropsy mainly include enteritis, peritonitis, edema, and bleeding from fish gills, muscles, and other internal organs. A preliminary diagnosis can be made by the clinical symptoms and necropsy changes, and final diagnosis requires virological examination after sampling.

Foreign Standards
The diagnostic procedures recommended by the OIE's Diagnostic Manual for Aquatic Animals include immunohistochemistry, fluorescent antibody technology, cell culture, ELISA and PCR techniques.

Prevention and Control (Immunization, Monitoring, Disinfection, Restriction, Destruction, Medication, etc.)
When the water temperature is above 20˚C, the squid body can produce higher levels of interferon and antibodies to withstand the SVCV attack. Therefore, to date, there have been no reports of SVC outbreaks in the tropics and subtropics. tions, but no SVCV nucleic acid vaccine has been reported to date. Ahne and some people believe that more studies are needed in the future to establish models and standards for the development of aqua vaccines [5]. The future development criteria for SVCV vaccines (including live, inactivated, subunit, and nucleic acid vaccines) should depend on the vaccine's effectiveness, safety, availability of local regulations and compliance with local epidemiological conditions. Consequence Assessment. The key issue now is that the SVC has a high mortality rate when it is popular in foreign countries, but there has not been a large-scale outbreak in China. Preliminary studies have shown that it is not fully adapted between the virus and the Chinese salmon strain. According to monitoring data in recent years, SVCV may be mutating and become more and more adaptable to Chinese cultured species, making it an SVC susceptibility species. If we do not take effective measures now, let SVC's epidemic go unchecked and the outbreak of the outbreak will only happen sooner or later. The consequences will be unthinkable. According to the statistics of the Ministry of Agriculture, the production of carp aquaculture in China accounts for more than 20% of the freshwater yield, and the carp species accounts for more than 50% of the freshwater aquaculture production. Once a large-scale outbreak happens, it is likely to have a devastating effect on the nation's salmon farming industry, much worse than the impact of white spot disease on shrimp.

Risk Assessment
Carangid fish is a traditional and popular cultured species in many provinces and cities in China. It has large aquaculture production and is a delicious food on people's

Overview of Current Laws and Regulations in China
The new version of the "Category of Category I, II and III Animal Diseases" issued by the Ministry of Agriculture at the end of 2008 classified SVC as a category I animal disease. Article 31 of these regulations specifies the control and extinguishing measures that should be taken when a type 1 animal epidemic occurs.

Regulations of the OIE "International Animal Health Code"
The international organizations that control the occurrence and spread of SVC  Chinese scholars have been actively conducting research on various aspects of SVC.

Hygienic Requirements for Commodities
SVC can be spread through the cross-border transport of sprout, and can also be transmitted vertically through parent fish spawning. Every year, a large number of parent fish and roe are imported from abroad, and the risk of pathogen introduction through these sprouts is extremely high. Therefore, when imported related sprouts, they must have a full certificate of origin, health certificate and other certificates.