Abstract
Porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly contagious disease and brings huge economic losses to commercial pork production worldwide. PRRSV causes severe reproductive failure in sows and respiratory distress in piglets. To trace the evolution of PRRSV in pigs with respiratory diseases in some regions of China, 112 samples were collected from nine provinces in China during 2016–2018. All samples were detected by RT-PCR and analyzed by the Nsp2/ORF5 (ORF5a)-genes-phylogeny. Sequence analysis and recombination analysis were conducted on the Nsp2/ORF5 (ORF5a) genes of the identified strain in the study. The RT-PCR result shown that the positive rate of PRRSV was 50.89% (57/112). Phylogenetic analysis showed that the identified PRRSV strains were all NA genotype and belonged to lineage 1, 3, and 8. The Nsp2 gene of identified PRRSV strains exhibited nucleotide homologies of 53.0 ~ 99.8%, and amino acid homologies of 46.8 ~ 99.7%. The ORF5 gene of identified PRRSV strains exhibited nucleotide homologies of 82.4 ~ 100%, and amino acid homologies of 79.6 ~ 100%. Sequence analysis revealed that a discontinuous 30-amino-acid deletion (positions 481 and 533–561) and a 131-amino-acid discontinuity deletion (positions 323–433, 481, and 533–551) in Nsp2 of PPRSV isolates; all identified strains in this study may be wild strains, and most identified strains may be highly virulent strains. Sequence analysis of ORF5 and ORF5a revealed that the mutation sites of GP5 were mainly concentrated in the signal peptide and epitopes region, while the mutation sites of ORF5a were mainly concentrated in the transmembrane and the intramembrane region. The recombination analysis indicated that there may be multiple recombination regions in identified strains, and the recombination pattern was more complex. This study showed that the prevalent PRRSV strain in some regions of China was still HP-PRRSV, while NADC30 strain also occupied a certain proportion; different types of PRRSV strains showed different patterns and variation in China. This study suggested that the monitoring of PRRSV prevalence and genetic variation should be further strengthened.
Highlights
Porcine reproductive and respiratory syndrome (PRRS) is a major threat to the global swine industry, causing significant economic losses each year
112 samples from nine provinces or municipalities of China were detected for PRRS virus (PRRSV) by RT-PCR
The sources of the samples in different regions were non-uniform, the results showed that the presence of PRRSV was severe in some parts of China
Summary
Porcine reproductive and respiratory syndrome (PRRS) is a major threat to the global swine industry, causing significant economic losses each year. The causative agent is PRRS virus (PRRSV), a member of the Arteriviridae family, order Nidoviridales. PRRSV was first reported in commercial pigs by the United States in 1987 [5], and the disease quickly spread worldwide with frequent break outs. PRRSV is still considered a highly contagious disease in the pig industry and creates huge economic losses [1, 6, 7]. Nsp and ORF5 (ORF5a) are highly variable and ORF5 is associated with the neutralizing epitope [13, 14]. They are usually used as target genes for PRRSV molecular epidemiological surveillance
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