A recombinant type 2 porcine reproductive and respiratory syndrome virus between NADC30-like and a MLV-like: Genetic characterization and pathogenicity for piglets

Highlights

• The genomic characterization of a type 2 PRRSV (TJnh1501) was analyzed.

• The isolate TJnh1501 was shown to the recombinant virus between NADC30-like and MLV-like.

• The isolate TJnh1501 shared intermediate virulence for piglets.

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) is an economically important pathogen for swine industry worldwide. The recombination occurring among PRRSV strains has been recognized as one of important molecular mechanisms for the evolution of PRRSV. Current prevalence of PRRSV NADC30-like causing clinical disease outbreaks is highly concerned in China. In the present study, the genetic characterization of a recombinant type 2 PRRSV (designated TJnh1501) was analyzed and its pathogenicity for piglets was examined. Our study showed that each region of TJnh1501 genome had 96.67–100% nucleotide and 96.5–100% amino acid identities with a Chinese highly pathogenic PRRSV-derived modified-live virus (MLV)-like except for its nonstructural protein 2 (nsp2)-coding region; while its nsp2-coding region shared higher nucleotide (84.44–85.85%) and amino acid (82.44–84.79%) identities with NADC30 and NADC30-like CHsx1401, and in particular, the highly variable region of nsp2 exhibited characteristic 131-aa deletion identical to NADC30 and NADC30-like CHsx1401. Meanwhile, we identified two recombination breakpoints located in the nt1737 and nt3506 of nsp2-coding region, which had higher nucleotide homology with NADC30 and NADC30-like CHsx1401. Moreover, TJnh1501 infection could cause persistent fever, moderate respiratory clinical signs, higher viremia, and obvious gross and microscopic lung lesions in piglets. The virus was shown to have lower pathogenicity than HP-PRRSV JXwn06, but higher than NADC30-like CHsx1401 for piglets. Our findings reveal that TJnh1501 is a recombinant type 2 PRRSV from the recombinant event between NADC30-like and MLV-like derived from the Chinese highly pathogenic PRRSV, and it exhibits intermediate virulence for pigs. This study adds valuable evidence for understanding the role of genomic recombination in the evolution of PRRSV.

Introduction

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically important diseases in swine industry worldwide (Neumann et al., 2005, Pejsak et al., 1997), which is characterized by reproductive failure in pregnant sows and respiratory distress in all ages of pigs (Albina, 1997, Rossow, 1998). The causative agent of this disease, PRRS virus (PRRSV), was first recognized in the Europe and the United States (Benfield et al., 1992, Collins et al., 1992, Wensvoort et al., 1991). To date, this virus continues to frustrate efforts to eliminate infection of pig herds through various strategies. PRRSV, belonging to the genus Arterivirus of the family Arteriviridae (Cavanagh, 1997), is an enveloped, single-stranded, positive-sense RNA virus with a genome of approximately 15 kb in size (Conzelmann et al., 1993, Meulenberg et al., 1997). The genome of PRRSV contains at least 12 overlapping open reading frames (ORFs) (Johnson et al., 2011, Li et al., 2015, Snijder and Meulenberg, 1998). The ORF1a and ORF1b encode two replicase polyproteins—pp1a and pp1ab, respectively, which are autoproteolytically processed into 16 nonstructural proteins (nsps), including nsp1α, nsp1β, nsp2, nsp2TF, nsp2N, nsp3, nsp4, nsp5, nsp6, nsp7α, nsp7β, and nsp8, and nsp9–12; the ORFs 2 to 7 encode the structural proteins, including five minor envelope proteins (GP2a, E, GP3, GP4, and ORF5a), two major envelope proteins (GP5 and M), and the nucleocapsid protein (N) (Kappes and Faaberg, 2015, Lunney et al., 2016). In addition, the nsp2 of PRRSV has been recognized to be an integral membrane protein as a structural protein (Kappes et al., 2013, Kappes et al., 2015). PRRSV is classified into two genotypes, the European type 1 and the North American type 2 with a divergence of ~ 40% at the nucleotide level and marked antigenic differences (Mardassi et al., 1994, Meng et al., 1995, Murtaugh et al., 1995, Nelson et al., 1993, Nelsen et al., 1999). Rapid evolution and variation of PRRSV always leads to the emergence of novel and more virulent viruses causing the outbreaks of clinical PRRS (Han et al., 2006, Karniychuk et al., 2010, Tian et al., 2007, Wang et al., 2015). The recombination occurring among PRRSV strains has been described under laboratory condition and in the field (Li et al., 2009, Liu et al., 2011, Shi et al., 2013, Yuan et al., 1999), which is considered to be one of important molecular mechanisms in the evolution of PRRSV.

The diversity of type 2 PRRSV in China is increasing currently along with the extensive use of modified-live virus (MLV) vaccines on pig farms (Han et al., 2017, Zhou et al., 2014). Importantly, the prevalence and transmission of novel PRRSV NADC30-like not only led to clinical PRRS outbreaks in China in many pig-producing areas in recent years (Li et al., 2016a, Li et al., 2016b, Ji et al., 2016, Sun et al., 2016, Zhou et al., 2015), but also caused recombination events with field strains or MLV of PRRSV, resulting in the generation of recombinant viruses (Li et al., 2016c, Wang et al., 2016, Zhang et al., 2016, Zhao et al., 2015). In the present study, we described the genetic characterization of a recombinant type 2 PRRSV between NADC30-like and MLV-like, and meanwhile analyzed its pathogenicity for piglets.