Whole-genome analysis of the recombination and evolution of newly identified NADC30-like porcine reproductive and respiratory syndrome virus strains circulated in Gansu province of China in 2023

Porcine reproductive and respiratory syndrome virus (PRRSV) remains one of the major threats to swine industry, resulting in huge economic losses worldwide. Currently, PRRSV has diversified into multiple lineages with characteristics of extensive recombination in China. In this research, three virus strains were isolated and four virus whole genome sequences were generated and analyzed from clinical samples collected in Gansu province of China in 2023. The four virus strains were designated GSTS4-2023, GSLX2-2023, GSFEI2-2023 and GSBY4-2023. Phylogenetic analysis based on ORF5 sequences showed that GSTS4-2023, GSLX2-2023, GSFEI2-2023 and GSBY4-2023 shared 91.7, 91.2, 93.2 and 92.9% homology with NADC30 strain respectively, and belonged to lineage 1 of PRRSV-2. In addition, one amino acid deletion was observed at position 33 in ORF5 of GSTS4-2023, GSLX2-2023 and GSFEI2-2023. Moreover, amino acid alignment of the four strains showed a typical discontinuous 131-amino acid (aa) deletion in NSP2 for NADC30-like virus strains. Recombination analysis revealed that all four strains originated from NADC30 (lineage 1), with their minor parents coming from JXA1-like strains (lineage 8), VR-2332-like strains (lineage5) and QYYZ-like strains (lineage3). Finally, the three isolated virus strains, GSTS4-2023, GSLX2-2023 and GSFEI2-2023 showed relatively low levels of replication in cell culture. Our findings provide important implications for the field epidemiology of PRRSV.

Pathogenicity Studies of NADC34-like Porcine Reproductive and Respiratory Syndrome Virus LNSY-GY and NADC30-like Porcine Reproductive and Respiratory Syndrome Virus GXGG-8011 in Piglets

The porcine reproductive and respiratory syndrome virus (PRRSV) has caused significant economic losses to the swine industry. The U.S., China, and Peru have reported NADC30-like or NADC34-like PRRSV-infected piglets, which have been identified as the cause of a significant number of abortions in clinics. Although the pathogenicity of NADC30-like PRRSV and NADC34-like PRRSV in piglets exhibits significant variability globally, studies on their pathogenicity in China are limited. In this study, the animal experiments showed that within 8-14 days post-infection, both piglets infected with NADC30-like PRRSV GXGG-8011 and those infected with NADC34-like PRRSV LNSY-GY exhibited significant weight loss compared to the control piglets. Additionally, the viremia of the LNSY-GY persisted for 28 days, while the viremia of piglets infected with the GXGG-8011 lasted for 17 days. Similarly, the duration of viral shedding through the fecal-oral route after the LNSY-GY infection was longer than that observed after the GXGG-8011 infection. Furthermore, post-infection, both the LNSY-GY and GXGG-8011 led to pronounced histopathological lesions in the lungs of piglets, including interstitial pneumonia and notable viral colonization. However, the antibody production in the LNSY-GY-infected group occurred earlier than that in the GXGG-8011-infected group. Our research findings indicate that LNSY-GY is a mildly pathogenic strain in piglets, whereas we speculate that the GXGG-8011 might be a highly pathogenic strain.

Molecular Characteristics and Pathogenicity of a Novel Recombinant Porcine Reproductive and Respiratory Syndrome Virus Strain from NADC30-, NADC34-, and JXA1-Like Strains That Emerged in China

Recently, the emergence of a NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV), which causes a large number of abortions in swine herds, has raised great concern in China. In this study, a PRRSV variant strain, PRRSV/CN/FJGD01/2021, evolved from recombination between NADC30-like, NADC34-like, and JXA1-like viruses was isolated in Fujian province in 2021, and its pathogenicity in piglets was examined. Animal experiments demonstrated that PRRSV/CN/FJGD01/2021 infection could induce 100% morbidity and cause higher viremia, a persistently higher fever (>40°C for 14 consecutive days), significant weight loss, and severe histopathological lung lesions compared to the NADC30-like FJZ03 strain and NADC34-like FJ0908 strain in piglets. The PRRSV/CN/FJGD01/2021 strain displayed higher pathogenicity than the FJZ03 and FJ0908 strains, but lower pathogenicity than the Chinese highly pathogenic (HP)-PRRSVs in piglets. Moreover, the Ingelvac PRRS modified live vaccine (MLV) provides incomplete cross-protection against heterologous PRRSV/CN/FJGD01/2021 in piglets. Our findings contribute to the understanding of the current epidemic situation of NADC34-like PRRSV in China. IMPORTANCE The pathogenicity of NADC34-like PRRSV has broad variations in virulence. Importantly, NADC34-like PRRSV has undergone complex recombination with local strains since it first emerged in 2017 in China. However, the pathogenicity of the recombinant NADC34-like virus was rarely experimentally evaluated in pigs. In this study, a novel PRRSV strain, PRRSV/CN/FJGD01/2021, was isolated from sows enduring a high-abortion-rate (20%) period in China in 2021. Notably, phylogenetic and recombination analyses revealed that PRRSV/CN/FJGD01/2021 is a recombinant virus from NADC30-, NADC34-, and JXA1-like isolates. PRRSV/CN/FJGD01/2021 was shown to cause higher virus load, persistent fever, significant weight loss, moderate respiratory clinical signs, and severe histopathological lung lesions in piglets. PRRSV/CN/FJGD01/2021 exhibited higher pathogenicity than NADC30-like FJZ03 and NADC34-like FJ0908, but lower than Chinese HP-PRRSVs for piglets. These data indicated that PRRSV/CN/FJGD01/2021 has intermediate virulence for piglets. Furthermore, the Ingelvac PRRS MLV could partly provide protective efficacy against PRRSV/CN/FJGD01/2021 challenge in piglets.

Genetic characterization and pathogenicity of a novel recombinant PRRSV from lineage 1, 8 and 3 in China failed to infect MARC-145 cells

The diversity of porcine reproductive and respiratory syndrome virus (PRRSV) in China is increasing rapidly along with mutation and recombination. Recombination could occur between inter- and intra-lineage of PRRSV, which accelerated the complexity of pathogenicity and cell tropism of the recombinant strain. In the present study, a novel PRRSV strain named HN-YL1711 was isolated from a pig farm suffering from severe respiratory difficulty in Henan province, China. The whole genomic sequence analysis indicated that the genome of HN-YL1711 was 15018 nt. It shared 86%, 87.3%, 88.1%, 91.1%, 84.2%, and 84.1% nucleotide similarities with PRRSVs VR2332, CH1a, JXA1, NADC30, QYYZ, and GM2, respectively. Based on phylogenetic analysis of Nsp2, ORF5 and complete genomes, HN-YL1711 was classified into lineage 1 of PRRSV. However, seven genomic break points were detected in recombination analysis, which indicated that the HN-YL1711 originated from multiple recombination among NADC30-like (major parent, lineage 1), JXA1-like (minor parent, lineage 8), and QYYZ-like (minor parent, lineage 3) PRRSV. Porcine alveolar macrophages (PAMs), 3D4/21-CD163 and MARC-145 cells were used to explore the viral adaptation of HN-YL1711. The results indicated that it could infect the PAMs but failed to infect MARC-145 cells. Challenge experiments showed that HN-YL1711 exhibits intermediate virulence in pigs, compared with HP-PRRSV JXA1 and LP-PRRSV CH1a. Taken together, our findings suggest that recombination remains an important factor in PRRSV evolution and that recombination further complicates the cell tropism and pathogenicity of PRRSV.

Recent Advances in Porcine Reproductive and Respiratory Syndrome Virus NADC30-Like Research in China: Molecular Characterization, Pathogenicity, and Control

The name porcine reproductive and respiratory syndrome virus (PRRSV) NADC30-like was first coined in 2015. It originated from the NADC30 strain that was introduced into China by importing breeding pigs and has since undergone mutations or recombination, resulting in variant viruses. Following widespread outbreaks in China in recent years, these NADC30-like strains have presented major health challenges in swine production systems. Outcomes induced by PRRSV NADC30-like infection are highly variable, ranging from inapparent to severe, depending on the recombination between NADC30 and field PRRSV strains prevalent in swine farms. Vaccines and strict biosecurity measures have been explored to fight this disease; however, current PRRSV commercially modified-live virus vaccines (MLVs) have the potential to revert to virulence and only provide limited or no cross-protection efficacy against NADC30-like strains. PRRSVs will remain an ongoing challenge to the swine industry until safe and effective vaccines or antiviral reagents are developed.

Porcine reproductive and respiratory syndrome virus NADC30-like strain accelerates Streptococcus suis serotype 2 infection in vivo and in vitro

Porcine reproductive and respiratory syndrome (PRRS), an economically significant pandemic disease, commonly results in increased impact of bacterial infections, including those by Streptococcus suis (S. suis). In recent years, PRRS virus (PRRSV) NADC30-like strain has emerged in different regions of China, and coinfected with S. suis and PRRSV has also gradually increased in clinical performance. However, the mechanisms involved in host innate responses towards S. suis and their implications of coinfection with NADC30-like strain remain unknown. Therefore, the pathogenicity of NADC30-like strain and S. suis serotype 2 (SS2) coinfection in vivo and in vitro was investigated in this study. The results showed that NADC30-like increased the invasion and proliferation of SS2 in blood and tissues, resulting in more severe pneumonia, myocarditis, and peritonitisas well as higher mortality rate in pigs. In vitro, NADC30-like strain increased the invasion and survival of SS2 in porcine alveolar macrophages (PAM) cells, causing more drastic expression of inflammatory cytokines and activation of NF-ĸB signalling. These results pave the way for understanding the interaction of S. suis with the swine immune system and their modulation in a viral coinfection.

Recombination in lineage 1, 3, 5 and 8 of porcine reproductive and respiratory syndrome viruses in China

Porcine reproductive and respiratory syndrome (PRRS) is one of the most important viral swine diseases, resulting in immense economic losses in Chinese pig industry. Currently, four major lineages: lineage 1 (NADC30-like), 3 (QYYZ-like), 5.1 (VR2332-like) and 8.7 (JXA1-like) of type 2 PRRSV (North American type) have been circulating in China based on classification system, which have caused concern about the potential of virus recombination. In the present study, a novel variant of PRRSV strain named FJLIUY-2017 was isolated from abortion rate (25%) in pregnant gilts in Fujian Province in China in 2017. To further our knowledge about the novel virus strain, we characterized the complete genome of FJLIUY-2017. Comparison to PRRS sequences in GenBank confirmed the absence of close relatives (<92%), but indicated FJLIUY-2017 belonged to NADC30-like PRRSV. The full length of FJLIUY-2017 was determined to be 15017 nucleotides (nt), excluding the poly(A) tail, shared 86.2-86.6% identity with JXA1-like strains (JXA1, TJ and FJYR), 88.9-90.6% with NADC30-like PRRSVs (NADC30, FJZ03 and CHsx1401), 86.4-86.5% with VR2332-like (VR2332, RespPRRS MLV and BJ-4) and only 60.8% with LV (European type). Recombination analyses revealed genomic breakpoints in structural (ORF3, ORF4 and ORF7) and nonstructural (Nsp1, Nsp2, Nsp6, Nsp9, Nsp11 and Nsp12) regions of the genomes with evidence for recombination events between lineages 1, 3, 5.1 and 8.7. Taken altogether, the results of our study provide further confirmation that PRRSV is prone to undergo recombination events. Thus, it is critical to monitor PRRSV evolution in China and establish an effective strategy for the control of PRRS.

Evolutionary analysis of six isolates of porcine reproductive and respiratory syndrome virus from a single pig farm: MLV-evolved and recombinant viruses

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important pathogens with economic significance for swine industry globally. The virus is characterized by its genetically extraordinary variability and diversified strains due to high mutation frequency and recombination rates. In the current study, we analyzed the genomes of six PRRSV strains isolated in different years from a single pig farm practicing HP-PRRSV-derived modified-live virus (MLV) vaccination in China, and in detail dissected their evolutionary relationship to MLV vaccines. The results show that all the six isolates belong to type 2 PRRSV, and are clustered into two lineages (lineage 1 and 8) based on their ORF5 genes. Further comparative analyses of genomes and the characteristic amino acid sites show that both HeN1201 and HeN1502 are MLV-like strains evolved from the MLV HuN4-F112. Recombination analyses reveal that HeN1301 is a recombinant virus emerged from the recombination event between two MLV-like strains evolved from the MLV TJM-F92 and HuN4-F112, and HeN1501 is a recombinant virus between two MLV-like strains evolved from HuN4-F112, while HeN1401 and HeN1601 are recombinant viruses derived from the recombination between NADC30-like and a MLV-like strain evolved from TJM-F92. Our findings provide more evidence for the fact that MLV-derived from the Chinese HP-PRRSV can be evolved and reversed in the field and enrich the data about the recombination between the viruses evolved from MLV and newly infected strain of PRRSV. This study stresses the necessity for pig producers to restrain the use of HP-PRRSV MLV vaccines in the field.

Genomic sequence and virulence of a novel NADC30-like porcine reproductive and respiratory syndrome virus isolate from the Hebei province of China

Porcine reproductive and respiratory syndrome virus (PRRSV) is the causative agent of porcine reproductive and respiratory syndrome (PRRS), which results in immense economic losses in the swine industry. Outbreaks of disease caused by NADC30-like PRRSV are of great concern in China. Here, a novel variant, NADC30-like PRRSV strain HB17A, was analyzed and its pathogenicity in pigs was examined. The full-length genome sequence of HB17A shared 83.6-95.1% nucleotide similarity with NADC30-like and NADC30 PRRSV without any gene insertions, but with a unique 2-amino acid deletion in Nsp2. A phylogenetic analysis showed that HB17A clustered with NADC30 strains. Different degrees of variation in the signal peptide, transmembrane region (TM), primary neutralizing epitope (PNE), non-neutral epitopes, and N-glycosylation sites were observed in GP5. Challenge experiments showed that HB17A infection resulted in persistent fever, moderate respiratory clinical signs, low levels of viremia and viral loads in serum, and mild gross and microscopic lung lesions. Moreover, IFN-γ, IL-6, and IL-10 cytokine levels were significantly elevated in serum, but the levels of IFN-α and IL-2 were similar to those of the negative controls. HB17A was less pathogenic but was secreted longer in nasal discharge than HP-PRRSV FZ06A. Our findings indicate that HB17A is a novel NADC30-like strain with certain deletions and mutations but with no evidence of genomic recombination. This strain exhibits intermediate virulence in pigs. This research will be help define the evolutionary characteristics of Chinese NADC30-like PRRSV.

An Attenuated Highly Pathogenic Chinese PRRS Viral Vaccine Confers Cross Protection to Pigs against Challenge with the Emerging PRRSV NADC30-Like Strain

A novel PRRSV strain was isolated in China that was genetically similar to the NADC30 strain which is reported to have spread throughout China. The objective of the present study was to evaluate the cross-protective efficacy of the live vaccine TJM-F92 in young pigs against challenge with a NADC30-like strain, HN201605. Twenty-five PRRSV- and antibody-free pigs were randomly divided into the following five groups: Vac/ChA, Unvac/ChA, Vac/ChB, Unvac/ChB and the mock. The pigs in groups Vac/ChA and Vac/ChB were inoculated intramuscularly with 1 mL TJM-F92 (10^5.0 TCID₅₀/mL). At 28 days post vaccination (0 days post challenge), groups Vac/ChA and Unvac/ChA were inoculated intranasally with 10^4.5 TCID₅₀/mL PRRSV strain TJ F3 (2 mL/pig), while groups Vac/ChB and Unvac/ChB were inoculated, using the same route, with the same dose of the NADC30-like strain HN201605 F3. Protective effects of the PRRSV strain were observed in all pigs in the Vac/ChA and Vac/ChB groups. Neither high fever nor signs of clinical disease were observed through the experiment in these groups, whereas pigs in Unvac/ChA group exhibited serious clinical symptoms, pathological lesions, and weight loss. In Unvac/ChB group, pigs developed milder clinical symptoms, which demonstrated that the NADC30-like strain HN201605 had moderate pathogenicity. The results suggest that the MLV vaccine strain TJM-F92 is an effective and safe vaccine candidate for use in China.

Genomic analysis of a recombinant NADC30-like porcine reproductive and respiratory syndrome virus in china

Recently, NADC30-like porcine reproductive and respiratory syndrome viruses (PRRSVs), which are genetically similar to the NADC30 strain isolated in the United States of America in 2008, have become prevalent in China. Here, a novel variant PRRSV strain named HNhx was successfully isolated on porcine alveolar macrophages from Henan province and the full-length genome sequence was determined. Phylogenetic analysis indicated that HNhx strain was classified into the NADC30-like PRRSV subgroup, in which all the strains had the unique discontinuous 131-amino acid deletion relative to that of the nonstructural protein 2 (Nsp2) of the VR2332 strain. Genetically, HNhx shared 92.9% nucleotide similarity to NADC30. Furthermore, HNhx strain contained extensive amino acid mutations in GP5. In particular, the S32H, N33D, D34N, and S36G variations resulted in that HNhx lost all the putative N-linked glycosylation sites at amino acid positions 30, 32, 33, 34, and 35. Recombination analysis revealed that HNhx was the result of recombination between the NADC30 strain and the highly pathogenic PRRSV vaccine strain circulating in China in Nsp4 (nt 5261) to Nsp9 (nt 7911). The novel genome data of HNhx will be helpful for understanding the evolution and epidemiology of PRRSV in China.

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

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.

Efficacy evaluation of three modified-live virus vaccines against a strain of porcine reproductive and respiratory syndrome virus NADC30-like

Porcine reproductive and respiratory syndrome reproductive virus is a devastating pathogen causing tremendous economic losses to swine production worldwide. Emergence of novel and variant PRRSV strains always leads to variable protection efficacy of modified-live virus (MLV) vaccines. Prevalence of PRRSV NADC30-like recently emerging in China has brought about clinical outbreaks of the disease. In the present study, the pathogenicity of a NADC30-like strain CHsx1401 for piglets was analyzed, and the potential cross-protective efficacy of three MLV vaccines including two commercial MLV vaccines and an attenuated low pathogenic PRRSV against this virus was further evaluated in piglets. The NADC30-like CHsx1401 was shown to cause fever, respiratory clinical signs, and lung gross and microscopic lesions of the inoculated piglets, suggesting that this virus is moderate virulent for piglets. Vaccination of piglets with the MLV vaccines could not reduce the clinical signs and lung lesions, and was partially efficacious in the reduction of viral loads in sera upon NADC30-like CHsx1401 challenge, indicating that these three MLV vaccines provide extremely limited cross-protection efficacy against the NADC30-like virus infection. Additionally, Ingelvac PRRS MLV appeared to exert some beneficial efficiency in shortening the period of clinical fever and in improving the growth performance of the challenged pigs. Our findings give valuable guidance for the choice and use of PRRSV MLV vaccines to control NADC30-like virus infection in the field.

Recombination in JXA1-R vaccine and NADC30-like strain of porcine reproductive and respiratory syndrome viruses

Porcine reproductive and respiratory syndrome (PRRS) is considered one of the most devastating swine diseases worldwide, resulting in immense economic losses. PRRS virus (PRRSV) has undergone rapid evolution since its first recognition in 1990s. In the present study, a PRRSV strain named FJXS15 causing high morbidity and mortality was isolated from piglets and sows from a farm participating in vaccination in China. Phylogenetic and molecular evolutionary analyses revealed that FJXS15 was highly similar to the JXA1-R vaccine strain (a live attenuated virus vaccine strain derived from the highly pathogenic PRRSV JXA1) in the ORF1a (nt 901-)-ORF4 (-nt 419) coding regions, as well as to FJZ03 (lineage 1, NADC30-like) in the 5'-UTR, ORF5a-ORF7 coding regions, and 3'-UTR, suggestive of a natural recombination event. Recombination analyses showed that recombination events occurred in two inter-lineage recombination events between Lineages 1 and 8 based on based on classification system (Shi et al., 2010), and two recombination breakpoints at positions 1-1092 and 13771-15537 of the sequence alignment (with reference to the VR-2332 strain). Animal experiments demonstrated that FJXS15-infected animals had more severe histopathological lung lesions than did JXA1-R-infected and control groups. A 25% mortality rate was found in FJXS15-infected piglets, which was similar to that found with other Chinese HP-PRRSV strains. Thus, the recombinant virus is a highly virulent PRRSV. Moreover, this report provides evidence for inter-subgenotypic recombination between the JXA1-R vaccine virus and a circulating Lineage 1 virus.

Emergence of a novel highly pathogenic porcine reproductive and respiratory syndrome virus in China

From 2014 to 2015, four novel highly pathogenic PRRS virus (HP-PRRSV) strains named 14LY01-FJ, 14LY02-FJ 15LY01-FJ, and 15LY02-FJ were isolated from high morbidity (100%) and mortality (40%-80%) in piglets and sows in Fujian Province. To further our knowledge about these novel virus strains, we characterized their complete genomes and determined their pathogenicity in piglets. Full-length genome sequencing analysis showed that these four isolates were closely related to type 2 (North American type, NA-type) isolates, with 88.1%-96.3% nucleotide similarity, but only 60.6%-60.8% homology to the Lelystad virus (LV) (European type, EU-type). The full length of the four isolates was determined to be 15017 or 15018 nucleotides (nt), excluding the poly(A) tail. Furthermore, the four isolates had three discontinuous deletions (aa 322-432, aa 483, and aa 504-522) within hypervariable region II (HV-II) of Nsp2, as compared to the reference strain VR-2332. This deletion pattern in the four isolates is consistent with strain MN184 and strain NADC30 isolated from America. Phylogenetic and molecular evolutionary analyses indicated that these virulent strains originated from a natural recombination event between the JXA1-like HP-PRRSV (JXA-1 is one of the earliest Chinese HP-PRRSV strains; sublineage 8.7) and the NADC30-like (lineage 1) PRRSV. Animal experiments demonstrated that these four strains caused significant weight loss and severe histopathological lung lesions as compared to the negative control group. High mortality rate (40% or 80%) was found in piglets infected with any one of the four strains, similar to that found with other Chinese HP-PRRSV strains. This study showed that the novel variant PRRSV was HP-PRRSV, and it is therefore critical to monitor PRRSV evolution in China and develop a method for controlling PRRS.

Genome characterization of two NADC30-like porcine reproductive and respiratory syndrome viruses in China

Background

The recent emergence of NADC30-like porcine reproductive and respiratory syndrome virus (PRRSV) in vaccinated pigs arose more attentions for the high incidents of mutation and recombination of PRRSVs.

Findings

In this study, we determined full-length genome sequences of two NADC30-like PRRSV isolates from recent PRRSV outbreaks in China. Phylogenetic analysis showed that these two isolates were clustered in an independent branch together with NADC30, an American isolate in 2008. Genetically, HNjz15 shared 95.6 % nucleotide similarity to NADC30 without any exotic gene insertion. By contrast, HNyc15 shared 93.8 % similarity to NADC30 with recombination with VR-2332 and CH-1a. Two more previously reported NADC30-like PRRSVs were also analyzed and had exotic gene insertions with different PRRSV strains in their nonstructural protein genes.

Conclusions

The above results showed the increased mutation and recombination rates of NADC30-like PRRSV under current vaccination pressure and a more pressing situation for the PRRSV eradication and control in China.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-016-3336-5) contains supplementary material, which is available to authorized users.

Pathogenicity comparison between highly pathogenic and NADC30-like porcine reproductive and respiratory syndrome virus

The pathogenicity of HNjz15, an NADC30-like strain of porcine reproductive and respiratory syndrome virus (PRRSV), was investigated and compared to that of a highly pathogenic PRRSV JAX1 strain. Six-week-old pigs infected with each virus showed typical clinical symptoms, including high fever and respiratory disorders. Pigs infected with JXA1 had more-severe clinical manifestations than pigs infected with HNjz15. HNjz15 replicated in vivo with kinetics similar to those of JXA1 but induced a lower level of PRRSV-specific antibody at the beginning of virus infection. Histopathologically, JXA1 infection led to more-severe lung lesions and broader organ tropism than HNjz15 did. Different from what was observed with the previously reported NADC30-like PRRSV JL580 strain, all HNjz15-infected pigs survived until the end of the study. All of these results indicated that NADC30-like PRRSV HNjz15 is virulent to pigs but is less pathogenic than the JXA1 and JL580 PRRSV strains.