Characterization of Classical Swine Fever Virus Associated with Defective Interfering Particles Containing a Cytopathogenic Subgenomic RNA Isolated from Wild Boar.

Abstract

ABSTRACT. Classical swine fever virus (CSFV) strain WB82, isolated from a wild boar in 1982, induced a distinct cytopathic effect (CPE) in primary swine testicle cell culture and in most of the porcine cell lines. This strain of CSFV was found to be composed of two biotypes, cytopathogenic (cp) CSFV, as a minor population, and noncytopathogenic (noncp) CSFV, as a major population. The noncp CSFV (designated strain WB82/E + ) was obtained by biological cloning, and it showed the exaltation of Newcastle disease virus phenomenon. In Northern blot analysis and RT-PCR assay, CSFV RNA with a subgenomic (sg) length was detected in addition to full-length viral RNA only in the cells in which a CPE had been revealed. These RNAs represent the genomes of typical defective interfering (DI) particles because of the strict dependence on a complementing helper virus and interference with replication of the helper virus. The sg RNA, which exhibits the genomes of the DI particles, lacked the nucleotides of the viral genomic region from N pro to NS2 (4764 bases). When extracted sg RNA was transfected to the cells infected with the WB82/E + strain, a distinct CPE was observed. Interestingly, the CPE was observed in cells infected with other heterologous noncp CSFV ALD and GPE -strains by sg RNA transfection. The results suggested that these noncp CSFVs act as helper viruses for the replication of sg RNA (DI particles). It was also shown that the cytopathogenicity of strain WB82 is caused by apoptosis. KEY WORDS: classical swine fever virus, DI particle, subgenomic RNA.

Cytopathogenicity of Classical Swine Fever Virus Correlates with Attenuation in the Natural Host

“…Interestingly, all cp CSFV field isolates analyzed so far consist of a non-cp CSFV helper virus together with a cp viral subgenome that lacks the genomic region encoding the structural proteins as well as the NS proteins N pro , p7, and NS2 (2,36,51). In addition, several studies reported on the generation of helper virus-independent (HVI) cp CSFV.…”

Characterization of Helper Virus-Independent Cytopathogenic Classical Swine Fever Virus Generated by an In Vivo RNA Recombination System

“…Interestingly, all cp CSFV field isolates analyzed so far consist of a noncp CSFV strain together with a viral subgenome. With the exception of subgenome cpBW1, which lacks 4,746 nucleotides (nt) (24), all other subgenomes are characterized by a common internal deletion of 4,764 nt, resulting in fusion of the translation initiation codon to the first codon of the NS3 gene (1,24,35). It could be demonstrated that the deletion of these CSFV subgenomes represents the genetic basis for expression of large amounts of NS3 and cytopathogenicity.…”

“…The respective subgenomes are defective interfering particles (DI) dependent on the presence of a helper virus for packaging (37). Such strains were isolated not only from domestic pig and wild boar but also from tissue culture cells in which noncp CSFV was passaged (1,35,39).To study various aspects of RNA recombination, we recently established the first in vivo RNA recombination system for pestiviruses which allowed the efficient generation of cp BVDV strains in cell culture (17). Here, we report on an analogous approach for CSFV.…”

“…The respective subgenomes are defective interfering particles (DI) dependent on the presence of a helper virus for packaging (37). Such strains were isolated not only from domestic pig and wild boar but also from tissue culture cells in which noncp CSFV was passaged (1,35,39).…”

An Overview of the Immune Evasion Strategies Adopted by Different Viruses with Special Reference to Classical Swine Fever Virus

“…A rare cytopathogenic (cp) form can occur spontaneously in cell culture [70] and has also been found in wild boar [71]. Its significance in CSFV pathogenesis is unknown.…”