The porcine reproductive and respiratory syndrome virus (PRRSV) can cause reproductive barriers in breeding pigs and respiratory symptoms in piglets. In this review, we summarize research progress of the infection and replication mechanisms of the PRRSV. We also review the virulence determinants of the PRRSV. All these fundamental studies are important for the control and elimination of the PRRSV.
Animals ; Porcine Reproductive and Respiratory Syndrome ; virology ; Porcine respiratory and reproductive syndrome virus ; genetics ; pathogenicity ; physiology ; Swine ; Virulence ; Virus Replication

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be a threat, causing economically significant impacts on the swine industry worldwide. Unfortunately, the traditional control strategies and conventional vaccines fail to provide sustainable disease control, in particular against genetically diverse strains, as they suffer from both antigenic heterogeneity and various immune evasion strategies of PRRSV. In this paper, latest research progress in immunology and immune evasion of PRRSVis summarized to provide a referenc for PRSSV prevention and control as well as the design of new vaccines.
Animals ; Immune Evasion ; Porcine Reproductive and Respiratory Syndrome ; immunology ; virology ; Porcine respiratory and reproductive syndrome virus ; genetics ; immunology ; Swine ; Viral Proteins ; genetics ; immunology

The objectives of the present study were to evaluate the anatomic localization of porcine reproductive and respiratory syndrome virus (PRRSV) in naturally infected pigs and to determine whether oral fluid could be used to detect the virus in infected animals. Two sows, seven 2-month-old grower pigs, and 70 6-month-old gilts were included in this study. PRRSV in sera and oral fluid were identified by nested reverse transcription PCR (nRT-PCR) while lung, tonsil, and tissue associated with oral cavity were subjected to nRT-PCR, immunohistochemistry, and in situ hybridization. In sows, PRRSV was identified in oral fluid and tonsils. PRRSV was also detected in oral fluid, tonsils, salivary glands, oral mucosa, and lungs of all seven grower pigs. However, viremia was observed in only two grower pigs. Double staining revealed that PRRSV was distributed in macrophages within and adjacent to the tonsillar crypt epithelium. In gilts, the North American type PRRSV field strain was detected 3 to 8 weeks after introducing these animals onto the farm. These results confirm previous findings that PRRSV primarily replicates in tonsils and is then shed into oral fluid. Therefore, oral fluid sampling may be effective for the surveillance of PRRSV in breeding herds.
Animals ; Female ; In Situ Hybridization/veterinary ; Lung/virology ; Male ; Palatine Tonsil/virology ; Polymerase Chain Reaction/veterinary ; Porcine Reproductive and Respiratory Syndrome/*virology ; Porcine respiratory and reproductive syndrome virus/*physiology ; Saliva/*virology ; Salivary Glands/virology ; Swine/virology ; Virus Replication/physiology

In recent years, mass outbreaks of highly pathogenic (HP) porcine reproductive and respiratory syndrome virus (PRRSV) have spread all over the Chinese swine industry. Based on the first infectious cDNA clone of HP PRRSV strain pJX143 and that of an attenuated PRRSV, pAPRRS, constructed in our group, we constructed several chimeric clones with various substitutions of structural protein genes (ORF4-7) and 3' UTR between attenuated pAPRRS and virulent pJX143.Upon transfection of MA-104 cultured cells, all chimeric constructs pSX12, p5NX12, and p56N12 were rescued. The rescued viruses maintained the similar virological properties, based on the results of the growth curve of the rescued viruses. To test if the chimeric viruses can be used as a vaccine candidate, vSX12 and v56N12 vaccinated pigs were challenged with the HP PRRSV JX143 strain. As a result, the vSX12 vaccinated pigs were all seroconverted by 14-day-post vaccination, while v56N12 vaccinated pigs showed poor antibody response. Upon challenge, the vSX12-vaccinated group showed no signs of clinical PRRS syndrome, and virema period was shorten to 6 days post-challenge. Our results demonstrated that 1) vSX12 chimeric virus is a good vaccine candidate; 2) the virulence determinants of HP PRRSV probably located in coding regions other than ORF3-7 and 3' UTR, as our chimeric viruses were proved to be attenuated.
Animals ; Cloning, Molecular ; Open Reading Frames ; Porcine Reproductive and Respiratory Syndrome ; virology ; Porcine respiratory and reproductive syndrome virus ; genetics ; immunology ; Recombinant Fusion Proteins ; genetics ; immunology ; Recombination, Genetic ; genetics ; Swine ; Vaccines, Attenuated ; immunology ; Viral Envelope Proteins ; Viral Proteins ; biosynthesis ; genetics ; Viral Vaccines ; immunology

To develop an attenuated vaccine against the highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) virus, the HP-PRRS virus strain TJ was attenuated by serial passages and plaque cloned every 5 to 10 passages in Marc-145 cells. Genetic variation and pathogenicity of HP-PRRSV strain TJ in the course of attenuation were analyzed. The results showed that the strain TJ sustained various sequence changes during the course of attenuation. Fifty-eight amino acids changes and a new continuous 120 amino acids deletion after the discontinuous 30 amino acids deletion (sites 481 and 533-561) occurred in strain TJ passages 140, and the position of 120 amino acids deletion was between 628 to 747 according to VR-2332. Animal test showed that the pathogenicity of strain TJ passages 20 was attenuated obviously, so we presume that genetic variation in nonstructural protein nsp2-nsp5, nsp7 and structural protein GP5 during the attenuation provides the molecular bases for the observed attenuated phenotype.
Amino Acid Sequence ; Animals ; Genetic Variation ; Molecular Sequence Data ; Porcine Reproductive and Respiratory Syndrome ; virology ; Porcine respiratory and reproductive syndrome virus ; classification ; genetics ; isolation & purification ; pathogenicity ; Sequence Deletion ; Serial Passage ; Swine ; Vaccines, Attenuated ; genetics ; isolation & purification ; Virulence

During the period from January to December of 2001, a total of 3,391 swine sera were submitted to our laboratory from 256 farms for the diagnosis of porcine reproductive and respiratory syndrome (PRRS). The antibody to porcine reproductive and respiratory syndrome virus (PRRSV) was tested by the indirect immunofluorescent antibody (IFA) test. Of the 256 farms tested, 230 farms (89.8%) were positive for the PRRSV antibody. The overall seroprevalence of the PRRSV antibody was 52.1% (1765/3391). Most of the pigs seemed to be infected with PRRSV at around 50 to 60 days old. The seroprevalence of the antibody became higher with age, and peaked at around 100 days old. More than one-third of the adult pigs, including boars, gilts, and sows, was positive for the PRRSV antibody. The infection of PRRSV was chronic and confined to growers and/or finishers in most farms. However, the antibody was detected in all production phases at some farms.
Age Factors ; Animals ; Antibodies, Viral/blood ; Female ; Fluorescent Antibody Technique, Indirect/veterinary ; Korea/epidemiology ; Male ; Porcine Reproductive and Respiratory Syndrome/diagnosis/epidemiology/*virology ; Porcine respiratory and reproductive syndrome virus/immunology/*isolation &purification ; Seroepidemiologic Studies ; Sex Factors ; Swine

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the important pathogens causing serious economic losses to swine industry worldwide. PRRSV is genetically and pathologically heterogenous. PRRSV NT0801 strain was isolated in a pig farm with clinical signs and had high pathogenesis in piglets. But its NSP2 gene did not have 30 amino acids deletion as highly pathogenic JXA1 strain. To elucidate the genetic characteristics of PRRSV NT0801 strain, the full-length genome of NT0801 isolate was sequenced and analyzed. The results showed that the genome of PRRSV NT0801 was 15439bp in length, including 29nt Poly(A) tail. Compared with the highly pathogenic JXA1 strain, it had the nucleotide sequence identity of 96.7%, amino acid sequence homology of 97.2% and 98.5% in GP3 and GP5, respectively. Phylogenetic analysis indicated that NT0801 isolate was located between the traditional strain and the highly pathogenic strain. But no obvious recombination signal was observed, compared with other PRRSV isolates with different virulence. The alignment of amino acid sequence of NT0801 with other PRRSV isolates demonstrated that three out of nine sites, being consistent with the highly pathogenic strain, were different from those in highly pathogenic while same as those in traditional strains and JXA1 vaccine strain. And one out of 9 sites was same as that of JXA1 vaccine strain exclusively, two out of 9 sites were different from all the strains. These results indicated that PRRSV NT0801 strain is closely related to highly pathogenic PRRSV, although there has no 30 amino acids deletions in NSP2 region. The epidemic PRRSV strains variation results from the gene mutation. It should be useful for studying on the virulence genes located in different ORFs of PRRSV in the future.
Amino Acid Sequence ; Animals ; China ; Genome, Viral ; Molecular Sequence Data ; Phylogeny ; Porcine Reproductive and Respiratory Syndrome ; virology ; Porcine respiratory and reproductive syndrome virus ; genetics ; isolation & purification ; Sequence Homology, Amino Acid ; Swine

The capability of porcine reproductive and respiratory syndrome virus (PRRSV) to be shed in semen for extended periods of time has been suggested to be a principal factor for viral transmission via insemination. In attempts to gain insights into the mechanism of PRRSV persistence in boars, tissue distribution and sites of viral infection were investigated by in situ hybridization (ISH) using digoxigenin-labeled RNA probe and the ISH results were compared with those of reverse transcription-nested polymerase chain reaction (RT-nested PCR). Animals were intranasally inoculated with 104 median tissue culture infectious dose of PRRSV VR-2332 and tissues collected at different times were examined. At day 7 postinfection, limited number of hybridization positive signals was observed in cells within or between seminiferous tubules in the testis sections while relatively abundant hybridization positive signals were observed in the brain stem and tracheobronchial lymph node. At later days of infection, hybridization positive signals were observed in cells within seminiferous tubules with much reduced frequency. Lack of agreement with the RT-nested PCR assay results in testis tissues obtained at days 14, 28, and 59 postinfection suggested that PRRSV infection in the testis may be extremely restricted, and may not necessarily constitute a major viral source in semen during extended periods of seminal shedding.
Animals ; Brain Stem/virology ; Endopeptidase K/metabolism ; *In Situ Hybridization ; Lymph Nodes/virology ; Male ; Microwaves ; Porcine Reproductive and Respiratory Syndrome/transmission/*virology ; Porcine respiratory and reproductive syndrome virus/*genetics/*isolation & purification ; RNA Probes ; Reverse Transcriptase Polymerase Chain Reaction ; Semen/virology ; Seminiferous Tubules/virology ; Sensitivity and Specificity ; Sexually Transmitted Diseases, Viral/transmission/veterinary/virology ; Swine/*virology ; Testis/virology

Porcine reproductive and respiratory syndrome virus (PRRSV) RNA load in sera and tissues during acute phase of infection was evaluated using a PCR- based quantitative assay. More than 80% of infected pigs (21/25) showed the peak level of viral RNA concentrations in serum (up to 8.6 x 108 copies/ml) at day 5 postinfection (PI), and started to clear the virus from the systemic circulation thereafter. Regression analysis using the viral RNA concentrations in sera obtained from days 5 to 14 PI showed that the viral RNA was cleared at the rate of 0.37 log reduction in the number of PRRSV RNA copies per day. It was estimated to be day 27 PI when the viral RNA in the serum of infected pigs becomes undetectable. When correlation analysis was performed between the systemic clearance rate and viral RNA concentrations in tissues of 9 infected pigs obtained at day 14 PI, moderately strong negative correlation was observed in the thymus (r = - 0.62) and brain stem (r = - 0.48), suggesting the capability of host animal to clear PRRSV from the systemic circulation appears to be related to the viral activity in the thymus and brain stem.
Animals ; Brain Stem/virology ; Eye/virology ; Female ; Logistic Models ; Lymphoid Tissue/virology ; Male ; Porcine Reproductive and Respiratory Syndrome/blood/*virology ; Porcine respiratory and reproductive syndrome virus/*genetics/*isolation & purification ; RNA, Viral/*analysis ; Reference Standards ; Reverse Transcriptase Polymerase Chain Reaction ; Swine/*virology ; Time Factors ; *Viral Load ; Viremia/veterinary/virology

The high genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) has been an obstacle to developing an effective vaccine for porcine reproductive and respiratory syndrome (PRRS). This study was performed to assess the degree of genetic diversity among PRRSVs from Korean pig farms where wasting and respiratory syndrome was observed from 2005 to 2009. Samples from 786 farms were tested for the presence of PRRSV using reverse transcription PCR protocol. A total of 117 farms were positive for type 1 PRRSV while 198 farms were positive for type 2. Nucleotide sequences encoding the open reading frame (ORF) 5 were analyzed and compared to those of various published PRRSV isolates obtained worldwide. Sequence identity of the ORF 5 in the isolates was 81.6~100% for type 1 viruses and 81.4~100% for type 2 viruses. Phylogenetic analysis of the ORF 5 sequences showed that types 1 and 2 PRRSVs from Korea were mainly classified into three and four clusters, respectively. The analyzed isolates were distributed throughout the clusters independent of the isolation year or geographical origin. In conclusion, our results indicated that the genetic diversity of PRRSVs from Korean pig farms is high and has been increasing over time.
Animal Husbandry ; Animals ; *Genes, Viral ; *Genetic Variation ; Lung/virology ; Lymph Nodes/virology ; *Open Reading Frames ; Phylogeny ; Porcine Reproductive and Respiratory Syndrome/virology ; Porcine respiratory and reproductive syndrome virus/chemistry/classification/*genetics/isolation & purification ; Republic of Korea ; Reverse Transcriptase Polymerase Chain Reaction/veterinary ; Sequence Analysis, DNA/veterinary ; Sequence Analysis, Protein/veterinary ; Swine