Analysis of molecular variation in porcine reproductive and respiratory syndrome virus in China between 2007 and 2012

Research progress on the N protein of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) is a highly contagious disease caused by the porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV exhibits genetic diversity and complexity in terms of immune responses, posing challenges for eradication. The nucleocapsid (N) protein of PRRSV, an alkaline phosphoprotein, is important for various biological functions. This review summarizes the structural characteristics, genetic evolution, impact on PRRSV replication and virulence, interactions between viral and host proteins, modulation of host immunity, detection techniques targeting the N protein, and progress in vaccine development. The discussion provides a theoretical foundation for understanding the pathogenic mechanisms underlying PRRSV virulence, developing diagnostic techniques, and designing effective vaccines.

Variations in the NSP4 gene of the type 2 porcine reproductive and respiratory syndrome virus isolated in China from 1996 to 2021

Porcine reproductive and respiratory syndrome virus (PRRSV) has continuously mutated since its first isolation in China in 1996, leading to difficulties in infection prevention and control. Infections caused by PRRSV-2 strains are the main epidemic strains in China, as determined by phylogenetic analysis. In this study, we focused on the prevalence and genetic variations of the non-structural protein 4 (NSP4) from PRRSV-2 over the past 20 years in China. The fundamental biological properties of the NSP4 were predicted, and an analysis and comparison of NSP4 homology at the nucleotide and amino acid levels was conducted using 123 PRRSV-2 strains. The predicted molecular weight of the NSP4 protein was determined to be 21.1 kDa, and it was predicted to be a stable hydrophobic protein that lacks a signal peptide. NSP4 from different strains exhibited a high degree of amino acid (85.8-100%) and nucleotide sequence homology (81.0-100%). Multiple amino acid substitutions were identified in NSP4 among 15 representative PRRSV-2 strains. Phylogenetic analysis showed that the lineage 8 and 1 strains, the most prevalent strains in China, were indifferent clades with a long genetic distance. This analysis will help fully elucidate the parameters of the PRRSV NSP4 epidemic in China to lay a foundation for adequate understanding of the function of NSP4. Genetic information results from the accumulation of conserved and non-conserved sequences. The high conservation of the NSP4 gene determines the most basic life traits and functions of PRRSV. Analyzing the spatial structure of NSP4 protein and studying the genetic evolution of NSP4 not only provide the theoretical basis for how NSP4 participates in the regulation of the innate response of the host but also provide a target for genetic manipulation and a reasonable target molecule and structure for new drug molecules.

Generation and Evaluation of Recombinant Baculovirus Coexpressing GP5 and M Proteins of Porcine Reproductive and Respiratory Syndrome Virus Type 1

Porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen of the porcine reproductive and respiratory syndrome, which is one of the most economically devastating diseases of the swine industry. However, whether the inactivated vaccine and modified live attenuated vaccines are effective in disease control is still controversial. Although several groups developed PRRSV virus-like particles (VLPs) as a vaccine against PRRSV, all these VLP-based vaccines targeted PRRSV-2, but not PRRSV-1 or both. Therefore, it is urgent to produce VLPs against PRRSV-1. In this study, we rescued recombinant baculovirus expressing GP5 and M proteins of PRRSV-1 through the Bac-to-Bac^® baculovirus expression system. Thereafter, PRRSV VLP was obtained efficiently in the recombinant baculovirus-infected High Five insect cells. Moreover, the PRRSV VLP and PRRSV VLP+A5 could efficiently trigger specific humoral immune responses and B cellular immune responses through intranasal immunization. The combination of PRRSV VLP and A5 adjuvant could improve the level of the immune response. The PRRSV-1 VLPs generated in this study have greater potential for vaccine development to control PRRSV-1 infection.

Construction and optimization of Lactobacillus plantarum expression system expressing glycoprotein 5 of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) causes serious reproductive failure and respiratory disease in pigs. Although numerous vaccines were developed against the virus, licensed vaccines showed limited efficacy. Here, we describe the construction and optimization of Lactobacillus plantarum expression system of PRRSV GP5 gene. The wild-type truncated GP5 or codon-optimized truncated GP5 was linked with endogenous signal peptide and target peptides (DCpep or Mpep) at 5' and 3' end of the gene, respectively. Then, the fragments were cloned into the L. plantarum expression plasmid pSIP411 and expressed under the induction of SppIP. As a result, PRRSV GP5 genes with optimized codons have higher expressions than that of the GP5 genes with wild-type codons, indicating codons optimization is an effective way to enhance the expression of an exogenous gene in L. plantarum. Further analysis showed that the codon-optimized GP5 with endogenous signal peptide can be effectively displayed on the surface of the L. plantarum, and the GP5 harboring target peptide Mpep displayed the highest antigenicity than the others. The highest production of PRRSV GP5 was obtained under the following conditions: L. plantarum harboring the plasmid pSIP-1320-O5MH are induced with 200 ng/mL SppIP at 33 °C for 7 h.

Co-Infection of Swine with Porcine Circovirus Type 2 and Other Swine Viruses

Porcine circovirus 2 (PCV2) is the etiological agent that causes porcine circovirus diseases and porcine circovirus-associated diseases (PCVD/PCVAD), which are present in every major swine-producing country in the world. PCV2 infections may downregulate the host immune system and enhance the infection and replication of other pathogens. However, the exact mechanisms of PCVD/PCVAD are currently unknown. To date, many studies have reported that several cofactors, such as other swine viruses or bacteria, vaccination failure, and stress or crowding, in combination with PCV2, lead to PCVD/PCVAD. Among these cofactors, co-infection of PCV2 with other viruses, such as porcine reproductive and respiratory syndrome virus, porcine parvovirus, swine influenza virus and classical swine fever virus have been widely studied for decades. In this review, we focus on the current state of knowledge regarding swine co-infection with different PCV2 genotypes or strains, as well as with PCV2 and other swine viruses.

Epidemiological and genetic characteristics of porcine reproductive and respiratory syndrome virus circulating in central and South China in 2016

Porcine reproductive and respiratory syndrome virus (PRRSV) is a leading cause of reproductive failure in sows and respiratory disorders in all ages of pigs; PRRSV is one of the most serious threats to the global pig industry. Continuously monitoring the epidemiological and genetic characteristics of PRRSV epidemic strains is beneficial for PRRSV prevention and control. In this study, we detected PRRSV from different types of porcine samples collected from 257 pig farms in Central (Henan Province) and South China (Fujian, Guangdong, and Guangxi Provinces) in 2016. Of the 1047 samples collected, 530 (50.62%) were positive for PRRSV by RT-PCR. The positive rates of virus detection for each of the geographical regions were higher than 44.25%. These findings suggest that the prevalence of PRRSV continues to be a major problem for the pig industry in China. Phylogenetic analysis showed that PRRSV2 was still the prevalent species in Central and South China, and highly pathogenic PRRSV (HP-PRRSV) was the predominate PRRSV type. However, the emergence and circulation of novel PRRSV strains such as the GM2-like strains and NADC30-like strains is worrisome and should receive more attention. In terms of different geographical regions, HP-PRRSV strains were the predominate PRRSV strains circulating in South China, while both HP-PRRSV strains and NADC30-like strains appeared to be the predominate PRRSV strains in Central China (Henan Province). These findings demonstrate that PRRSV types circulating in different regions in China are some different. In addition, a number of amino acid mutation types including amino acid changes and deletions were observed in both the GP5 and Nsp2 proteins. Our study provides important information on the epidemiological and genetic characteristics of PRRSV strains currently circulating in China.