Classical swine fever is a highly contagious disease that affects domestic and wild pigs worldwide. The causative agent of the disease is Classical swine fever virus (CSFV), which belongs to the genus Pestivirus within the family Flaviviridae. On the genome level, CSFV can be divided into three genotypes with three to four sub-genotypes. Those genotypes can be assigned to distinct geographical regions. Knowledge about CSFV diversity and distribution is important for the understanding of disease dynamics and evolution, and can thus help to design optimized control strategies. For this reason, the geographical pattern of CSFV diversity and distribution are outlined in the presented review. Moreover, current knowledge with regard to genetic virulence markers or determinants and the role of the quasispecies composition is discussed.

The homology of the sequences, reported and registered in GenBank, of different strains of Avian influenza virus (AIV), Newcastle disease virus (NDV), Classical swine fever virus (CSFV) and Foot-and-mouth disease virus (FMDV), was analysed and compared with each other. According to the properties of these viruses, the conservative domain of the M gene for AIV, the F gene for NDV, the 5' non-coding domain end for CSFV and the 2B gene for FMDV were selected for polymerase chain reaction (PCR) amplification. In order to prevent the formation of conformational dimers between different primers, four pairs of primers designed with the DNAsis system under the condition of G+C (50–60%),18–25 bp in length and Tm (72–85), were analysed using the VNTI5.5 system. The specific fragments amplified were as follows: 141 bp for FMDV, 200 bp for CSFV, 319 bp for NDV and 471 bp for AIV. The optimal conditions of PCR for each virus mentioned above were determined by orthogonal assay, and two or four of the four pairs of primers were then combined and used for amplification trials. The results showed that four specific fragments of different lengths would be successfully amplified in one tube at the same time. The products of PCR were tested to be specific by sequencing. Out of 46 pathological samples detected with the multiple PCR, there were 5 AIVs, 7 NDVs, 15 CSFVs and 6 FMDVs. The amplification above was identified with a single PCR. On the other hand, the results corresponded to those of electronic microscopy, haemagglutination (HA) and enzyme-linked immunosorbent assay (ELISA). The method described here is practicable, sensitive, specific, simple and cheap. It could be used for diagnosing AIV, NDV, CSFV and FMDV in different animals.

Most eukaryotic mRNAs require the cap-binding complex eIF4F for efficient initiation of translation, which occurs as a result of ribosomal scanning from the capped 5′ end of the mRNA to the initiation codon. A few cellular and viral mRNAs are translated by a cap and end-independent mechanism known as internal ribosomal entry. The internal ribosome entry site (IRES) of classical swine fever virus (CSFV) is ∼330 nt long, highly structured, and mediates internal initiation of translation with no requirement for eIF4F by recruiting a ribosomal 43S preinitiation complex directly to the initiation codon. The key interaction in this process is the direct binding of ribosomal 40S subunits to the IRES to form a stable binary complex in which the initiation codon is positioned precisely in the ribosomal P site. Here, we report the results of analyses done using enzymatic footprinting and mutagenesis of the IRES to identify structural components in it responsible for precise binding of the ribosome. Residues flanking the initiation codon and extending from nt 363–391, a distance equivalent to the length of the 40S subunit mRNA-binding cleft, were strongly protected from RNase cleavage, as were nucleotides in the adjacent pseudoknot and in the more distal subdomain IIId1. Ribosomal binding and IRES-mediated initiation were abrogated by disruption of helix 1b of the pseudoknot and very severely reduced by mutation of the protected residues in IIId1 and by disruption of domain IIIa. These observations are consistent with a model for IRES function in which binding of the region flanking the initiation codon to the decoding region of the ribosome is determined by multiple additional interactions between the 40S subunit and the IRES.