Abstract
BackgroundPorcine reproductive and respiratory syndrome virus (PRRSV) has caused several outbreaks in China since 2006. However, the genetic diversity of PRRSV in China has greatly increased by rapid evolution or recombination events. Modified live-attenuated vaccines are widely used to control this disease worldwide. Although the risk and inefficacy of the vaccine has been reported, the genetic diversity between epidemic field strains and vaccine strains in China has not been completely elucidated.MethodsA total of 293 clinical samples were collected from 72 pig farms in 16 provinces of China in 2015 for PRRSV detection. A total of 28 infected samples collected from 24 pig farms in nine provinces were further selected for immunohistochemical analysis and whole genome sequencing of PRRSV. Phylogenetic analysis and recombination screening were performed with the full genome sequences of the 28 strains and other 623 reference sequences of PRRSV.ResultsOf 293 clinical samples, 117 (39.93%) were positive for PRRSV by RT-PCR. Phylogenetic results showed that the 28 strains were nested into sublineage 10.5 (classic highly pathogenic [HP]-PRRSV), sublineage 10.6 (HP-PRRSV-like strains and related recombinants), sublineage 10.7 (potential vaccine JXA1-R-like strains), and lineage 9 (NADC30-like strains and recombinants of NADC30-like strains), respectively, suggesting that multiple subgenotypes of PRRSV currently circulate in China. Recombination analyses showed that nine of 28 isolates and one isolate from other laboratory were potential complicated recombinants between the vaccine JXA1-R-like strains and predominant circulating strains.ConclusionsThese results indicated an increase in recombination rates of PRRSV under current vaccination pressure and a more pressing situation for PRRSV eradication and control in China.
Highlights
Porcine reproductive and respiratory syndrome virus (PRRSV) has caused several outbreaks in China since 2006
These results indicated an increase in recombination rates of PRRSV under current vaccination pressure and a more pressing situation for PRRSV eradication and control in China
117 (39.93%) were positive for PRRSV detection by RT-Polymerase chain reaction (PCR), which was similar to that report in 2010 (45.2%) [17], suggesting that PRRSV was still prevalent in China in 2015
Summary
Porcine reproductive and respiratory syndrome virus (PRRSV) has caused several outbreaks in China since 2006. The genetic diversity of PRRSV in China has greatly increased by rapid evolution or recombination events. Porcine reproductive and respiratory syndrome (PRRS) is an economically critical swine disease worldwide that causes severe reproductive failure in sows, poor viability of piglets, and respiratory disease with secondary infection in growing pigs. American type (Type 2), share only about 60% nucleotide similarities at the genomic level and are represented by Lelystad virus and VR-2332, respectively [9,10,11]. Having evolved from a less-pathogenic variant in China, HP-PRRSV has widely spread and continues to cause high mortality and huge economic losses to the swine industry in China [15, 16]. Associated with the importation of NADC30like strains or recombination events between NADC30-
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