Importation and Recombination Are Responsible for the Latest Emergence of Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus in China

Abstract

cIn China, a majority of the highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRSV) strains were seeded by the 2006 outbreak. However, the most recently emerged (2013-2014) HP-PRRSV strain has a very different genetic background. It is a NADC30-like PRRSV strain recently introduced from North America that has undergone genetic exchange with the classic HP-PRRSV strains in China. Subsequent isolation and characterization of this variant suggest high pathogenicity, so it merits special attention in control and vaccine strategies. P orcine reproductive and respiratory syndrome (PRRS) is characterized by respiratory distress in nursery swine and reproductive failure in sows and has resulted in huge economic losses to the global swine industry since its first recognition in the United States in 1987 (1). In China, highly pathogenic PRRSV (HP-PRRSV) has been circulating and predominating in the field since the initial outbreak in 2006 and has resulted in the loss of more than one million pigs (2-5). Retrospective studies of that outbreak have shown that the highly pathogenic variant emerged from less pathogenic PRRSV strains in China (6), which were initially introduced from North America in the 1990s. CH-1a was the earliest representative of this group (7). Following the outbreak, more-stringent biosecurity controls and a targeted immunization campaign were undertaken to limit HP-PRRS in China.However, despite these measures, HP-PRRSV has experienced recurrent population expansions since the initial outbreak. One such reemergence was associated with genetic exchange between two HP-PRRSV viruses circulating in the field (8). Another recent outbreak (2013)(2014) is probably in the early stage of emergence. It has occurred in several provinces of China and is characterized by high fever, cough, anorexia, red discoloration of the body, and blue ears. Diseased pigs also have multiple visceral lesions. Their lungs display consolidation, and their lymph nodes are enlarged and hemorrhagic. The rates of morbidity and mortality due to this new HP-PRRSV are very high. An affected farm in Jilin Province had a morbidity rate of 100% and a mortality rate of 76.6% (230/ 300).We obtained the representative open reading frame 5 (ORF5) sequences from two farms that experienced the disease, i.e., JL580 and HLJ58 from Jilin Province and Heilongjiang Province, respectively. Phylogenetic analyses using the PhyML version 3.0 software (9) suggested that these viruses are distantly related to the classic HP-PRRSV strains in China, which belong to lineage 8 (Fig. 1A). Instead, they nested deeply within diverse lineage 1, which originated in Canada and is now prevalent in both the United States and Canada (10). Interestingly, the virus is also closely related to a group represented by NADC30, a moderately virulent strain isolated in 2008 in the United States (11). Furthermore, the phylogenetic topology of the diversity surrounding this new HP-PRRSV suggests, with high resolution, a transmission chain from Canada to the Unit...

Emergence of mosaic recombinant strains potentially associated with vaccine JXA1-R and predominant circulating strains of porcine reproductive and respiratory syndrome virus in different provinces of China

“…Recombination events between field PRRSV strains could result in greater PRRSV pathogenicity, such as strain JL580 from the recombination between NADC30 and HP-PRRSV 09HEN1, which has been confirmed as highly pathogenic [19]. In this study, the PRRSV-positive piglets exhibited severe clinical symptoms and gross lesions typical of HP-PRRS.…”

“…In 2006, a HP-PRRSV with a unique discontinuous 30-aa deletion in Nsp2 emerged and caused the most severe viral diseases in swine in China to date [15]. The genetic diversity of this HP-PRRSV has greatly increased by rapid evolution and recombination events [14, 17–19]. The current commercial PRRSV vaccines cannot provide complete protection against this disease [21].…”

“…In a second major outbreak in China and other Southeast Asian countries in 2009 and 2010, the HP-PRRSV strain was later shown to be a recombinant between two Chinese PRRSV strains [17, 18]. NADC30 was isolated in the US in 2008 and in China in 2013 [19]. Associated with the importation of NADC30-like strains or recombination events between NADC30-like and domestic strains in China, a third outbreak occurred from 2013 to 2015 [19–21].…”

“…NADC30 was isolated in the US in 2008 and in China in 2013 [19]. Associated with the importation of NADC30-like strains or recombination events between NADC30-like and domestic strains in China, a third outbreak occurred from 2013 to 2015 [19–21]. …”

Complete Genome Sequence of a Mosaic NADC30-Like Porcine Reproductive and Respiratory Syndrome Virus in China

“…According to the genetic and antigenic characteristics, PRRSVs can be divided into two major genotypes: European type (type 1) and North American type (type 2). Recently, several provinces in northeastern and central China had reported the outbreaks of NADC30-like PRRSVs, which shared high nucleotide similarity with NADC30 isolated in the United States in 2008 (3–5). Here, we report the complete genome sequence of the NADC30-like variant PRRSV HNhx.…”