classical swine fever virus

Other Scientific Names

• hog cholera virus

English acronym

• CSFV
• HCV

• Domain: Virus
•     Group: "Positive sense ssRNA viruses"
•         Group: "RNA viruses"
•             Order: Nidovirales
•                 Family: Flaviviridae
•                     Genus: Pestivirus
•                         Species: classical swine fever virus

Classical swine fever virus (CSFV) belongs to the species Pestivirus C, in the genus Pestivirus, within the family Flaviviridae (Smith et al., 2017). It has an RNA genome contained in a capsid of about 28 nm, surrounded by an envelope. The virion has a size of between 40 and 50 nm. The single-stranded linear RNA genome is infective and encompasses about 12.3 kilobases. The open-reading frame encodes one large polyprotein of 3898 amino acids that is cleaved by proteases to yield mature viral proteins. The open-reading frame is flanked by a 5’-noncoding region of almost 400 nucleotides and a 3’-noncoding region of about 200 nucleotides. The order of the gene products is as follows:

NH₂ -(N^pro-C-E^rns-E1-E2-p7-NS2.3-NS4A-NS4B-NS5A-NS5B)-COOH.

The left part of the genome is coding for the capsid (C) protein, and the three envelope (E) proteins (E1, E2 and E^rns). The E^rns protein has RNase activity, which is unique among virus proteins (Schneider et al., 1993; Hulst et al., 1994). The E2 is the most immunodominant and is composed of two independently formed antigenic domains (Rijn et al., 1994). The rest of the genome codes solely for nonstructural proteins, of which NS2-3 is the most conserved.

The differentiation of CSFV from bovine viral diarrhoea virus (BVDV) and border disease virus (BDV), which can both infect pigs, can easily be done on the basis of sequence differences in the 5’-noncoding region, the E2 and NS5B genes. The genome of CSFV is relatively stable (Vanderhallen et al., 1999; Widjojoatmodjo et al., 1999). CSFV strains can be divided into three genotypes and numerous sub-genotypes (Blome et al., 2017; OIE, 2020)

Antigenically, CSFV is closely related to BVDV and BDV, but by the use of monoclonal antibodies a clear distinction can be made (Wensvoort et al., 1989; Edwards et al., 1991).

The resistance to physical or chemical treatment is partly dependent on the virus strain and the material that contains the virus. For instance, in cell culture fluid virus was inactivated in 10 minutes at 60°C, whereas it was not inactivated in defibrinated blood at 68°C for 30 minutes (Torrey and Prather, 1963). The viral infectivity is quickly destroyed below pH 4 and above pH 11. Because the virus envelope contains lipids, solvents such as ether or detergents easily inactivate the virus. It can remain infectious in pork for months (Mebus et al., 1997), and can survive for weeks in liquid pig manure (Haas et al., 1995). For disinfection of tools, footwear, etc., 1-2% sodium hydroxide is still considered most suitable.

Normally, CSFV induces no or minimal cytopathology in cell culture. However, CSFV showed a cytopathic effect in bone marrow stroma cell cultures (Shimizu et al., 1995), and strains that contained defective interfering particles also gave rise to a cytopathic effect in cell culture (Meyers and Thiel, 1995; Kosmidou et al., 1998). Inactivation of the RNA activity of the E^rns protein also resulted in cytopathogenicity (Hulst et al., 1994) and in attenuation of the virus in the pig (Meyers et al., 1999).

There is a wide range in virulence among CSFV strains. Highly virulent strains cause acute severe disease often resulting in mortality, whereas strains with low virulence give rise to mild disease or subclinical infection.

The Classical Swine Fever Database (CSF-DB) of the EU and OIE Reference Laboratory for classical swine fever (online at http://viro60.tiho-hannover.de/eg/csf/) offers one of the world’s largest semi-public virus-specific sequence collections combined with a module for phylogenetic analysis. The CSF-DB allows for the storage and analysis of traditionally used, well established genomic regions and of larger genomic regions including complete viral genomes (Postel et al., 2016).

Classical swine fever, the disease associated with this pathogen, is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). For information from OIE, see: https://www.oie.int/en/animal-health-in-the-world/animal-diseases/classical-swine-fever/