Jing Xie

Genetic Characterization and Pathogenicity of a Novel Recombined Porcine Reproductive and Respiratory Syndrome Virus 2 among Nadc30-Like, Jxa1-Like, and Mlv-Like Strains

Recombination among porcine reproductive and respiratory syndrome viruses (PRRSVs), coupled with point mutations, insertions, and deletions occurring in the genome, is considered to contribute to the emergence of new variants. Here, we report the complete genome sequences of a PRRSV field strain, designated SCN17, isolated from a RespPRRS MLV-vaccinated piglet in China in 2017. Sequence alignment revealed that SCN17 had discontinuous 131-amino acid (111 + 1 + 19-aa) deletion in the NSP2-coding region identical to that of NADC30 when compared to VR-2332. Notably, the strain, SCN17, contained an additional 1-aa deletion in NSP2, a 1-aa deletion in ORF5, and a unique 3-nt deletion in the 3′-UTR. Phylogenetic analysis showed that SCN17 clustered into NADC30-like lineage based on ORF5 genotyping, whereas it belonged to an inter-lineage between the NADC30-like and VR-2332-like lineages as established based on the full-length genome. Importantly, the SCN17 was identified as a novel virus recombined between a NADC30-like (moderately pathogenic), a JXA1-like (highly pathogenic), and an attenuated vaccine strain, RespPRRS MLV (parental strain VR-2332). Furthermore, we tested its pathogenicity in piglets. SCN17 infection caused a persistent fever, moderate interstitial pneumonia, and increased the viremia and antibody levels in the inoculated piglets. Of note, all SCN17-infected piglets survived throughout the study. The new virus was showed to be a moderately virulent isolate and have lower pathogenicity than HP-PRRSV strain, SCwhn09CD. Our results provide evidence for the continuing evolution of PRRSV field strain by genetic recombination and mutation leading to outbreaks in the vaccinated pig populations in China.

Development and application of a novel Bio-Plex suspension array system for high-throughput multiplexed nucleic acid detection of seven respiratory and reproductive pathogens in swine.

The aim of this study was to develop a multiple PCR assay based on the suspension array system for the simultaneous detection of respiratory and reproductive pathogens in swine. Pseudorabies virus (PRV), Japanese encephalitis virus (JEV), classic swine fever virus (CFSV), African swine fever virus (ASFV), porcine circovirus type 2 (PCV-2), porcine reproductive and respiratory syndrome virus (PRRSV) and porcine parvovirus (PPV) are the major respiratory and reproductive viral pathogens in pig farms. Seven pairs of specific primers and probes were designed, and the multiple PCR was performed, with the PCR products hybridized to beads coupled to probes, which were then detected by Bio-Plex suspension array system. The limit of detection, specificity and repeatability of this method was determined. The assay was further tested using 137 clinical samples, and the results were compared with conventional PCR to evaluate the ability of the method to diagnose porcine viruses. The results showed that the assay had a high degree of specificity and repeatability, and the simultaneous detection limit for the seven viruses reached 103 copies/μL. Forty-nine of the clinical samples tested positive for at least one of the viruses, the principal viral infections in the clinical samples were PCV-2 and PRRSV. The suspension method represented a rapid, specific and high-throughput tool for single or mixed detection of the seven porcine viruses simultaneously, and has great significance for the development of liquid chip techniques for the diagnosis of diseases in animals.