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.

Outbreak Investigation of NADC30-Like PRRSV in South-East China

Epidemiological outbreak investigations were conducted on NADC30-like porcine reproductive and respiratory syndrome virus (PRRSV) to investigate the prevalence of the disease in south-east China in 2015. Two more provinces were found to have NADC30-like PRRSV circulating besides previously reported six provinces. Phylogenetic analysis showed that these virus isolates were clustered in an independent branch and shared high nucleotide similarity to NADC30, a type 2 PRRSV that has been isolated in Unite States in 2008. One NADC30-like PRRSV strain from Henan province was successfully isolated on porcine alveolar macrophages and was tested on 6-week-old specific pathogen-free pigs for pathogenic study. The virus-inoculated pigs showed typical PRRSV clinical symptoms, but all pigs survived throughout the study with a period of 14 days. At necropsy, the lungs of infected pigs developed PRRSV-specific interstitial pneumonia, and virus antigen was detected in lung samples. Therefore, our results indicated NADC30-like PRRSV has widely spread in China and could cause clinical disease on pigs.

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.