Abstract
Object: To analyze porcine reproductive and respiratory syndrome virus (PRRSV) strains from 13 infection cases via the N protein gene and its encoded amino acid sequence and to provide a theoretical basis for the epidemiological study, prevention and control of porcine reproductive and respiratory syndrome (PRRS). Methods: In clinically suspected PRRSV infections, viruses were isolated by extracting viral nucleic acid and amplifying the N protein gene by RT-PCR. Then, the product was purified and sequenced to acquire the whole gene sequence of the N protein and its encoded amino acid sequence. DNASTAR software was used to analyze the homology, the genetic evolution and the derivation of the variability of amino acids of the N protein gene from 13 PRRSV strains and classical domestic and foreign strains. Results: Among the thirteen strains of PRRSV isolated from this study, ten strains had the greatest homology with the JXA1 strain (98.9% - 100%), and they belonged to the sublineage 8.7. The remaining three strains had the greatest homology with the NADC30 strain (95.4% - 97.1%), and they belonged to lineage one. The analysis of the variability of N protein amino acids showed that there were high frequency mutations in the five loci of 13 isolated strains of PRRSV as follows: 15th amino acid (10/13), 46th amino acid (11/13), 91st amino acid (10/13), 109th amino acid (10/13), and 117th amino acid (10/13). Conclusion: In recent years, sublineage 8.7 was the dominant pedigree in field PRRSV epidemic strains in China with lineage one occupying a certain proportion of the field. Four high frequency mutations existed in N protein antigen epitopes of isolated strains from the region. The nuclear localization signal (NLS) structure, specifically the 46th amino acid residue of the N protein, was mutated and genetically stable.
Highlights
Caused by the porcine reproductive and respiratory syndrome virus (PRRSV), porcine reproductive and respiratory syndrome (PRRS) is one of the major infectious swine diseases
The sequencing results showed that the ORF7 gene from 13 strains of PRRSV did not have a base deletion or insertion in comparison with the traditional strains, and the gene mutations were in the partial sites
The homology of the ORF7 genes with the highly pathogenic PRRSV strains isolated from the domestic was 88.7% - 100% with the JXA1 strain, 87.1% - 91.7% with the FJFS strain, 89.3% - 97.1% with the NADC30 and JL58 strains, 89.2% - 96.5% with the classical strains CH-1a and CH-1R strains isolated from China, 89.5% - 94.4% with the vaccine MLV strain, 89.5% - 94.4% with the American standard VR-2332 strain, 89.2% 94.4% with the classical R98 strain, 55.6% - 58.3% with the European classical Lelystad strain, and 88.2% - 100% with the 11 previously isolated PRRSV strains
Summary
Caused by the porcine reproductive and respiratory syndrome virus (PRRSV), porcine reproductive and respiratory syndrome (PRRS) is one of the major infectious swine diseases. In 2006, an epidemic characterized by high fever, rubefaction and dyspnea emerged in swine farms in most areas of China Later, this epidemic was confirmed to have been caused by a PRRSV variant strain and was denominated as highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) because of its high morbidity [4]. This study shows that since the outbreak of HP-PRRS in 2006, domestic PRRSV isolates belong to highly pathogenic porcine reproductive and respiratory syndrome virus branches with a very high homology [5] Whether these isolates are from the vaccine virus is unknown, but it can be speculated that the field of PRRSV may be facing a new round of selection pressure, so maintaining epidemiological tracking of the field PRRSV-isolated strains is quite significant for the prevention and control of the disease
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