J Vet Sci.  2018 May;19(3):339-349. 10.4142/jvs.2018.19.3.339.

Genomic characterization and pathogenic study of two porcine reproductive and respiratory syndrome viruses with different virulence in Fujian, China

• Sui X
• Xin T
• Guo X
• Jia H
• Li M
• Gao X
• Wu J
• Jiang Y
• Willems L
• Zhu H
• Hou S

• KMID: 2412124
• DOI: http://doi.org/10.4142/jvs.2018.19.3.339

Abstract

Two strains of porcine reproductive and respiratory syndrome virus (PRRSV) were isolated in 2006 and 2016 and designated as FZ06A and FZ16A, respectively. Inoculation experiments showed that FZ06A caused 100% morbidity and 60% mortality, while FZ16A caused 100% morbidity without death. By using genomic sequence and phylogenetic analyses, close relationships between a Chinese highly pathogenic PRRSV strain and the FZ06A and FZ16A strains were observed. Based on the achieved results, multiple genomic variations in Nsp2, a unique N-glycosylation site (N³³â†’K³³), and a K151 amino acid (AA) substitution for virulence in the GP5 of FZ16A were detected; except the 30 AA deletion in the Nsp2-coding region. Inoculation experiments were conducted and weaker virulence of FZ16A than FZ06A was observed. Based on our results, a 30 AA deletion in the Nsp2-coding region is an unreliable genomic indicator of a high virulence PRRSV strain. The Nsp2 and GP5 differences, in addition to the virulence difference between these two highly pathogenic PRRSV strains, have the potential to be used to establish a basis for further study of PRRSV virulence determinants and to provide data useful in the development of vaccines against this economically devastating disease.

Keyword

genomics; phylogeny; porcine respiratory and reproductive syndrome virus; virulence

MeSH Terms

Asian Continental Ancestry Group
China*
Genomics
Humans
Mortality
Phylogeny
Porcine Reproductive and Respiratory Syndrome*
Porcine respiratory and reproductive syndrome virus*
Vaccines
Virulence
Vaccines

Figure

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  Fig. 1 Cytopathic effects of isolated porcine reproductive and respiratory syndrome virus cultured in Marc-145 cells. Infected Marc-145 cells became round and aggregated into clusters. (A) Non-infected Marc-145. (B) Virus-infected Marc-145 cells. Scale bars = 200 µm (A and B).

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  Fig. 2 Phylogenetic tree of 24 porcine reproductive and respiratory syndrome virus (PRRSV) isolates based on analysis of nucleotide sequences of the complete genomic sequences (A), Nsp2 (B), and ORF5 (C) of PRRSV strains by applying the distance-based neighbor-joining method in MEGA software (ver. 5.1) [31]. Bootstrap values were calculated on 1,000 replicates of the alignment.

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  Fig. 3 Mean rectal temperature in negative-control pigs and pigs infected experimentally with FZ06A and FZ16A porcine reproductive and respiratory syndrome virus. Significant differences between FZ06A-infected, FZ16A-infected and negative-control pigs were observed at most of the time point.

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  Fig. 4 Serum antibody levels over time. Values represent average titers from five animals. Dotted line at 0.4 sampleto-positive (S/P) ratio designates threshold value above which titers were considered positive for anti-porcine reproductive and respiratory syndrome virus antibodies. Data from groups of five pigs assessed by using one-way ANOVA (*p < 0.05, **p < 0.01, ***p < 0.001).

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  Fig. 5 Macroscopic observation of the lungs of the control (A) and highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV)-infected (B and C) pigs. No macroscopic (gross) lesions were recorded in the lungs collected from the control animals. (B) Severe multifocal lung lesions and consolidation of lung tissue in the HP-PRRSV FZ06A-infected group. (C) Mild multifocal lung lesions and consolidation of lung tissue in the HP-PRRSV FZ16A-infected group.

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  Fig. 6 Histopathological lesions in the lung of control (A) and highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) infected (B and C) pigs. Histological lesions were examined in the HP-PRRSV FZ06A- and FZ16A-infected groups and the challenge control by using H&E staining. (A) All lungs from control pigs failed to exhibit features of acute PRRSV infection. (B) Lung tissues collected from the HP-PRRSV FZ06A-infected pigs developed severe interstitial pneumonia with alveolar septal thickening and alveoli disappearance. (C) The lung tissues collected from HP-PRRSV FZ16A-infected pigs developed mild interstitial pneumonia and alveoli disappearance. Scale bars = 200 µm (A–C).

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