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Abstract
BackgroundPorcine reproductive and respiratory syndrome (PRRS) has leaded to an enormous loss per year to the swine industry, its etiology porcine reproductive and respiratory syndrome virus (PRRSV) is a highly mutated virus in pigs. To fully understand the genetic characteristics of PRRSV genome in South China, this study collected the lung samples infected with PRRSV in Guangdong and Hainan province from 2014 to 2015 and tried to isolate the PRRSV. Finally, the complete genomes of isolated strains were sequenced and analyzed.MethodsVirus isolation was performed in MARC-145 cells. The 13 fragments of PRRSV genome were amplified by RT-PCR and the complete PRRSV genome sequence was obtained by SeqMan program of DNASTAR7.0 software. Nucleotide and deduced amino acid (AA) sequences of NSP2 and ORF5 were aligned using the MegAlign program of DNASTAR7.0 software to determine sequence homology. A phylogenetic tree was constructed using MEGA5.2 software with the neighbor-joining method to analyze the evolutionary relationship.Results11 PRRSV strains were isolated in South China from 2014 to 2015. All the isolated strains clustered into subgenotype V along with the HP-PRRSV representative strains JXA1, HuN4 and JXwn06. The subgenotype V was furtherly divided into two groups. AA sequence alignment analysis indicated that all the isolated strains had 1 AA deletion and 29 AA continuous deletion at position 481 and 533-561. Notably, GDHY strain had another 120 AA continuous deletion at position 629-748. All the isolated strains had an A137S mutation in the residue A137 of GP5 which was considered to differentiate vaccine strains. All the isolated strains had a L39I mutation in the primary neutralizing epitope (PNE) of GP5. Except GDHZ had a N34T mutation, all the other isolated strains had conserved N30, N44 and N51 glycosylation sites in the four potential N-glycosylation sites (N30, N34, N44 and N51) of GP5.ConclusionsOur study showed that the prevalent strains in this region were highly pathogenic PRRS virus-like. Moreover, one new strain having another 120 amino acids continuous deletion except the discontinuous 30 (29+1) amino acids deletion in NSP2 region had emerged. Besides, the isolated strains had extensive amino acids substitutions in the putative signal, extravirion and intravirion regions of GP5. These results showed that PRRSV has undergone extensive variation in South China, providing some theoretical basis for researching effective vaccince to better controling the PRRSV in this area.
Highlights
Porcine reproductive and respiratory syndrome (PRRS) has leaded to an enormous loss per year to the swine industry, its etiology porcine reproductive and respiratory syndrome virus (PRRSV) is a highly mutated virus in pigs
The isolated strains had extensive amino acids substitutions in the putative signal, extravirion and intravirion regions of GP5. These results showed that PRRSV has undergone extensive variation in South China, providing some theoretical basis for researching effective vaccince to better controling the PRRSV in this area
Phylogenetic analysis of the isolated PRRSV genome To understand the evolution relationships of all the isolated PRRSV strains with the representative strains, phylogenetic trees were constructed using the neighorjoining method based on the complete genome, NSP2 nucleotide and ORF5 nucleotide sequences, respectively
Summary
Porcine reproductive and respiratory syndrome (PRRS) has leaded to an enormous loss per year to the swine industry, its etiology porcine reproductive and respiratory syndrome virus (PRRSV) is a highly mutated virus in pigs. The complete genomes of isolated strains were sequenced and analyzed. Porcine reproductive and respiratory syndrome (PRRS) is an important swine contagious disease across the world, leading to an enormous loss per year to the swine industry [1]. In 2006, a highly pathogenic strain of porcine reproductive and respiratory syndrome virus (HP-PRRSV) broke out in China and spreaded rapidly to most areas of China and neighboring countries [4,5,6]. The PRRSV complete genome is about 15 kb in length, including at least 10 open reading frames (ORFs): ORF1a, ORF1b, ORF2a, ORF2b, ORF3, ORF4, ORF5, ORF5a, ORF6 and ORF7 [11, 12]. ORF1a and ORF1b encode viral replicase polyproteins, which are furtherly cleaved into 16 nonstructural proteins (Nsps), including NSP1α, NSP1β, NSP2, NSP2TF, NSP2N, NSP3, NSP4, NSP5, NSP6, NSP7α, NSP7β, NSP8, NSP9, NSP10, NSP11 and NSP12 [13,14,15], whereas other ORFs encode the viral structural proteins GP2a, E, GP3, GP4, GP5, ORF5a, M, and N, respectively (12)
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