Complete genome sequence of an overattenuated highly pathogenic porcine reproductive and respiratory syndrome virus

JXA1-P170 is an overattenuated highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) that has been passaged in vitro 170 times. Vaccination with JXA1-P170 cannot protect pigs against JXA1 challenge. Compared with the parental virus JXA1, JXA1-P170 contains 1 nucleotide (nt) deletion and 113 nt mutations leading to 59 amino acid substitutions. Here we announce the first complete genome sequence of the overattenuated HP-PRRSV.     

Complete genome sequence of a highly pathogenic porcine reproductive and respiratory syndrome virus variant

Following the 2006 outbreaks of the highly pathogenic porcine reproductive and respiratory syndrome, the causative agent was identified as the highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV). To investigate whether the HP-PRRSV variant continues circulating and accelerating evolution, we sequenced and analyzed the complete genome of the identified HP-PRRSV field strain SD16. The sequence data indicate that the HP-PRRSV variant continues to prevail and accelerate evolution, especially in the nonstructural protein.     

Complete genome sequence of two novel Chinese virulent porcine reproductive and respiratory syndrome virus variants

A highly pathogenic strain of porcine reproductive and respiratory syndrome virus (PRRSV), characterized by a discontinuous 30-amino-acid deletion in its Nsp2-coding region, has been emerging in China since 2006. Here, we report the complete genomic sequence of two novel Chinese virulent PRRSV variants with additional NSP2-gene deletions, which will help us understand the molecular and evolutionary characteristics of PRRSV in Asia.     

Complete genome sequence of porcine reproductive and respiratory syndrome virus isolated from piglet stool samples

WUH4 is a highly pathogenic North American porcine reproductive and respiratory syndrome virus (PRRSV). Unlike previous PRRSV isolates, which were mainly recovered from sera or tissues, WUH4 was isolated from a piglet stool sample. Here we announce its complete genome sequence.     

The origin and evolution of porcine reproductive and respiratory syndrome viruses

Porcine reproductive and respiratory syndrome viruses (PRRSV) are divided into North American and European types, which show about 40% difference in their amino acid sequences. The divergence time of these two types has been estimated to be about 1980 from epidemiological data. This suggested that PRRSV have evolved at a higher evolutionary rate (order of 10(-2)/site/year) compared with other RNA viruses of 10(-3) to 10(-5)/site/year. Here, to test the evolutionary history of PRRSV speculated by the epidemiological background, we estimated the divergence time and evolutionary rate of PRRSV with molecular evolutionary analysis. Estimated divergence time (1972-1988) corresponded well to that estimated by the epidemiological data, and the evolutionary rate (4.71-9.8) x 10(-2) of PRRSV was indeed the highest among RNA viruses so far reported. Furthermore, we inferred important sites for the adaptation in order to examine how PRRSV have adapted to swine since they emerged. The adaptive sites were located not only in the epitopes related to immunity but also in the transmembrane regions including a signal peptide. In particular, the adaptive sites in the transmembrane regions were considered to affect compatibility to the host cell membrane. We conclude that PRRSV were transmitted from another host species to swine in about 1980 and have adapted to swine by altering the transmembrane regions.     

CD163 expression confers susceptibility to porcine reproductive and respiratory syndrome viruses

Direct functional screening of a cDNA expression library derived from primary porcine alveolar macrophages (PAM) revealed that CD163 is capable of conferring a porcine reproductive and respiratory syndrome virus (PRRSV)-permissive phenotype when introduced into nonpermissive cells. Transient-transfection experiments showed that full-length CD163 cDNAs from PAM, human U937 cells (histiocytic lymphoma), African green monkey kidney cells (MARC-145 and Vero), primary mouse peritoneal macrophages, and canine DH82 (histocytosis) cells encode functional virus receptors. In contrast, CD163 splice variants without the C-terminal transmembrane anchor domain do not provide PRRSV receptor function. We established several stable cell lines expressing CD163 cDNAs from pig, human, and monkey, using porcine kidney (PK 032495), feline kidney (NLFK), or baby hamster kidney (BHK-21) as the parental cell lines. These stable cell lines were susceptible to PRRSV infection and yielded high titers of progeny virus. Cell lines were phenotypically stable over 80 cell passages, and PRRSV could be serially passed at least 60 times, yielding in excess of 10(5) 50% tissue culture infective doses/ml.     

Complete genome sequence of porcine reproductive and respiratory syndrome virus strain QY2010 reveals a novel subgroup emerging in China

QY2010 is a highly pathogenic North American-type porcine reproductive and respiratory syndrome virus (PRRSV). The complete genome sequence shows that QY2010 shares low sequence identity (60 to 88.7%) to all known PRRSV isolates. Phylogenetic analyses further reveal that QY2010 constitutes a novel subgroup within the North American genotype of PRRSV.     

Overview: Replication of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV), an arterivirus that causes significant losses in the pig industry, is one of the most important animal pathogens of global significance. Since the discovery of the virus, significant progress has been made in understanding its epidemiology and transmission, but no adequate control measures are yet available to eliminate infection with this pathogen. The genome replication of PRRSV is required to reproduce, within a few hours of infection, the millions of progeny virions that establish, disseminate, and maintain infection. Replication of the viral RNA genome is a multistep process involving a replication complex that is formed not only from components of viral and cellular origin but also from the viral genomic RNA template; this replication complex is embedded within particular virus-induced membrane vesicles. PRRSV RNA replication is directed by at least 14 replicase proteins that have both common enzymatic activities, including viral RNA polymerase, and also unusual and poorly understood RNA-processing functions. In this review, we summarize our current understanding of PRRSV replication, which is important for developing a successful strategy for the prevention and control of this pathogen.     

A one-step RT-PCR assay to detect and discriminate porcine reproductive and respiratory syndrome viruses in clinical specimens

Outbreaks of highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) have led to large economic losses and, subsequently, have drawn great attention to its diagnosis and prevention. To facilitate rapid discrimination of HP-PRRSV from classical PRRSV (C-PRRSV), we developed a one-step RT-PCR assay. Primer specificities were evaluated with RNA extracted from 8 viral strains and our results revealed that the primers had a high specificity for PRRSV. The assay sensitivity was 25 copies/μL for both HP-PRRSV and C-PRRSV. A total of 929 serum samples were identified, of which 20.45% were HP-PRRSV-positive and 1.51% were C-PRRSV-positive, which was completely consistent with that of immunochromatochemistry and sequencing method. The proposed assay can detect the virus 2 days prior the onset of symptoms and it can be performed in 2 h, thereby providing a rapid method to discriminate HP-PRRSV from C-PRRSV for the identification and prevention of PRRSV infections.     

Divergence time of porcine reproductive and respiratory syndrome virus subtypes

Porcine reproductive and respiratory syndrome virus (PRRSV) recently emerged in domestic pigs of Western Europe and North America. Although time of emergence was identical on the two continents, genetic composition was markedly different with a clear geographical subtype structure, indicating that subtypes diverged in separate reservoirs prior to emergence. Genetic analyses have shown that the most recent common ancestor (MRCA) of Western European isolates existed around 1980 and that these originate from Eastern European pigs. These findings are challenged by a study of Hanada et al. who place the MRCA of all PRRSV isolates around 1980 and find that no significant subtype divergence occurred before emergence. Here, I discuss problems of information content, methodology, and biological plausibility associated with this study. Using alternative methodology, I reanalyze the existing data and conclude that the MRCA of all PRRSV isolates existed around 1880, 100 years before the date estimated by Hanada et al.     

Plant reproductive allocation predicts herbivore dynamics across spatial and temporal scales

Life-history theory suggests that iteroparous plants should be flexible in their allocation of resources toward growth and reproduction. Such plasticity could have consequences for herbivores that prefer or specialize on vegetative versus reproductive structures. To test this prediction, we studied the response of the cactus bug (Narnia pallidicornis) to meristem allocation by tree cholla cactus (Opuntia imbricata). We evaluated the explanatory power of demographic models that incorporated variation in cactus relative reproductive effort (RRE; the proportion of meristems allocated toward reproduction). Field data provided strong support for a single model that defined herbivore fecundity as a time-varying, increasing function of host RRE. High-RRE plants were predicted to support larger insect populations, and this effect was strongest late in the season. Independent field data provided strong support for these qualitative predictions and suggested that plant allocation effects extend across temporal and spatial scales. Specifically, late-season insect abundance was positively associated with interannual changes in cactus RRE over 3 years. Spatial variation in insect abundance was correlated with variation in RRE among five cactus populations across New Mexico. We conclude that plant allocation can be a critical component of resource quality for insect herbivores and, thus, an important mechanism underlying variation in herbivore abundance across time and space.     

Characterization of interaction between porcine reproductive and respiratory syndrome virus and porcine dendritic cells

The porcine reproductive and respiratory syndrome Virus (PRRSV) is an infectious disease that causes abortions and respiratory disorders in swine. In this study, the interaction between PRRSV and porcine dendritic cells generated from CD14(+) monocytes in the presence of GM-CSF and IL-4 was examined. As a result, it was shown that immature and mature dendritic cells can be productively infected with PRRSV. When the expression of surface MHC molecules on infected dendritic cells was determined, MHC classes I and II were found to be downregulated when compared with uninfected dendritic cells. With the exception of the IL-4 and IFN-gamma cytokines, the induction of the IL-10, IL-12, and TNF-alpha cytokines all increased in dendritic cells infected with PRRSV. A mixed lymphocyte reaction showed that peripheral blood mononuclear cells cocultured with PRRSVinfected dendritic cells were less stimulated than peripheral blood mononuclear cells cocultured with dendritic cells treated with PBS, LPS, or UV-inactivated PRRSV. Therefore, these results suggest that PRRSV would appear to modulate the immune stimulatory function of porcine dendritic cells.     

猪繁殖与呼吸综合征疫苗

针对猪繁殖与呼吸综合征(porcine reproductive and respiratory syndrome,PRRS),主要以疫苗预防为主.常规疫苗主要有灭活疫苗和弱毒疫苗,但前者的免疫原性差,保护效果不佳;后者又发现存在毒力返强的可能性,安全性低的问题.目前学者们主要集中在对猪繁殖与呼吸综合征病毒(PRRS virus,PRRSV)基因工程疫苗进行研究.本文就PRRS的灭活疫苗、弱毒疫苗和基因工程疫苗的研究进展做详细的阐述.     

Phosphorylation of the porcine reproductive and respiratory syndrome virus nucleocapsid protein

Porcine reproductive and respiratory syndrome virus (PRRSV) is a cytoplasmic RNA virus with the unique or unusual feature of having a nucleocapsid (N) protein that is specifically transported to the nucleolus of virus-infected cells. In this communication, we show that the N protein is a phosphoprotein. Phosphoamino acid analysis of authentic and recombinant N proteins demonstrated that serine residues were exclusively phosphorylated. The pattern of phosphorylated N protein cellular distribution in comparison with that of [(35)S]methionine-labeled N protein suggested that phosphorylation does not influence subcellular localization of the protein. Time course studies showed that phosphorylation occurred during, or shortly after, synthesis of the N protein and that the protein remained stably phosphorylated throughout the life cycle of the virus to the extent that phosphorylated N protein was found in the mature virion. Two-dimensional electrophoresis and acid-urea gel electrophoresis showed that one species of the N protein is predominant in virus-infected cells, suggesting that multiple phosphorylated isoforms of N do not exist.     

Antigen-specific B-cell responses to porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome virus (PRRSV) causes an acute, viremic infection of 4 to 6 weeks, followed by a persistent infection lasting for several months. We characterized antibody and B-cell responses to viral proteins in acute and persistent infection to better understand the immunological basis of the prolonged infection. The humoral immune response to PRRSV was robust overall and varied among individual viral proteins, with the important exception of a delayed and relatively weak response to envelope glycoprotein 5 (GP5). Memory B cells were in secondary lymphoid organs, not in bone marrow or Peyer's patches, in contrast to the case for many mammalian species. Potent anti-PRRSV memory responses were elicited to recall antigen in vitro, even though a second infection did not increase the B-cell response in vivo, suggesting that productive reinfection does not occur in vivo. Antibody titers to several viral proteins decline over time, even though abundant antigen is known to be present in lymphoid tissues, possibly indicating ineffective antigen presentation. The appearance of antibodies to GP5 is delayed relative to the resolution of viremia, suggesting that anti-GP5 antibodies are not crucial for resolving viremia. Lastly, viral infection had no immunosuppressive effect on the humoral response to a second, unrelated antigen. Taking these data together, the active effector and memory B-cell responses to PRRSV are robust, and over time the humoral immune response to PRRSV is effective. However, the delayed response against GP5 early in infection may contribute to the prolonged acute infection and the establishment of persistence.     

Complete genome sequences of two novel European clade bovine foamy viruses from Germany and poland

Bovine foamy virus (BFV), or bovine spumaretrovirus, is an infectious agent of cattle with no obvious disease association but high prevalence in its host. Here, we report two complete BFV sequences, BFV-Riems, isolated in 1978 in East Germany, and BFV100, isolated in 2005 in Poland. Both new BFV isolates share the overall genetic makeup of other foamy viruses (FV). Although isolated almost 25 years apart and propagated in either bovine (BFV-Riems) or nonbovine (BFV100) cells, both viruses are highly related, forming the European BFV clade. Despite clear differences, BFV-Riems and BFV100 are still very similar to BFV isolates from China and the United States, comprising the non-European BFV clade. The genomic sequences presented here confirm the concept of high sequence conservation across most of the FV genome. Analyses of cell culture-derived genomes reveal that proviral DNA may specifically lack introns in the env-bel coding region. The spacing of the splice sites in this region suggests that BFV has developed a novel mode to express a secretory but nonfunctional Env protein.     

Complete genome sequences of a Korean virulent porcine epidemic diarrhea virus and its attenuated counterpart

A virulent porcine epidemic diarrhea virus (PEDV) strain, DR13, was obtained from suckling pigs suspected of having porcine epidemic diarrhea in 1999 in Korea, and its attenuated counterpart was derived from virulent strain DR13 by serial propagation in Vero cells. This report describes the first complete genome sequences of virulent PEDV and its attenuated counterpart, which will provide important insights into the molecular basis of the attenuation of PEDV.