Fetal microscopic lesions in porcine reproductive and respiratory syndrome virus-induced abortion.
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Microscopic lesions in four cases of abortion caused by porcine reproductive and respiratory syndrome virus (PRRSV) were characterized by arteritis, myocarditis, and encephalitis. Fetal PRRSV infection was confirmed by virus isolation or immunohistochemistry and serology. Although fetal microscopic lesions in PRRSV abortions are rarely reported, diagnosticians should consider PRRSV when these lesions occur. (+info)
Sequence comparison of open reading frames 2 to 5 of low and high virulence United States isolates of porcine reproductive and respiratory syndrome virus.
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The sequences of ORFs 2 to 5 of five United States (US) porcine reproductive and respiratory syndrome virus (PRRSV) isolates with differing virulence were determined. The nucleotide and deduced amino acid sequences of these isolates were compared with those of other known PRRSV isolates. The amino acid sequence identity between seven US PRRSV isolates was 91-99% in ORF 2, 86-98% in ORF 3, 92-99% in ORF 4 and 88-97% in ORF 5. The low virulence US isolate had highest sequence variation in ORFs 2 to 4 compared to the other US isolates. A hypervariable region with antigenic potential was identified within the major envelope glycoprotein. Phylogenetic analysis of ORFs 2 to 7 indicated the existence of at least three minor genotypes within the major US genotype. The low virulence US isolate formed a branch distinct from the other US isolates. The results of this study have implications for both the taxonomy of PRRSV and vaccine development. (+info)
Comparative pathogenicity of nine US porcine reproductive and respiratory syndrome virus (PRRSV) isolates in a five-week-old cesarean-derived, colostrum-deprived pig model.
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One hundred forty-six 5-week- old cesarean-derived, colostrum-deprived (CDCD) pigs were inoculated intranasally with 1 of 9 US porcine reproductive and respiratory syndrome virus (PRRSV) isolates. Differences were found in severity of clinical respiratory disease, rectal temperatures (P < or = 0.001), gross lung lesions (P < or = 0.001), and microscopic lung lesions (P < or = 0.05). Gross lung lesions were generally most severe 10 days postinoculation and were distributed primarily in the cranial, middle, and accessory lobes and ventromedial portion of the caudal lung lobes. Mean gross lung lesion scores estimating the percentage of lung affected by pneumonia at 10 days postinoculation ranged from 16.7% +/- 2.8% (mean +/- SEM, n = 10) for isolate ISU-51 to 62.4% +/- 5.7% (n = 10) for isolate ISU-28. Microscopic lung lesions were characterized by hyperplastic and hypertrophied type 2 pneumocytes, septal infiltration by mononuclear cells, and accumulation of necrotic alveolar exudate. Lymph node follicular hyperplasia and focal necrosis was seen with all 9 isolates. This CDCD pig model was useful for demonstration of significant differences in pathogenicity among US PRRSV isolates. This difference in pathogenicity may help explain the variation of severity of clinical disease observed in field outbreaks of porcine reproductive and respiratory syndrome and should provide for meaningful comparison of PRRSV genotypes. (+info)
Detection of porcine reproductive and respiratory syndrome virus in cell cultures and formalin-fixed tissues by in situ hybridization using a digoxigenin-labeled probe.
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A nonradioactive in situ hybridization method is described for the detection of porcine reproductive and respiratory syndrome virus (PRRSV) in cell cultures and in formalin-fixed paraffin-embedded tissue sections originating from experimentally infected pigs and from 1 field case. A 174 bp cDNA probe targeting the viral RNA encoding the nucleocapsid protein of a Canadian PRRSV isolate was generated by polymerase chain reaction. The cDNA probe was labeled by random priming with digoxigenin-dUTP using a commercially available kit. The ability of the digoxigenin-labeled probe to specifically detect PRRSV RNA was tested on cultured cells infected with 6 Canadian PRRSV isolates, a US PRRSV isolate and the European Lelystad isolate. The probe detected all Canadian PRRSV isolates tested as well as the US PRRSV isolate but did not detect the Lelystad isolate. In addition, when tested on formalin-fixed paraffin-embedded tissue sections from pigs experimentally infected with several Canadian isolates and from a field case, a strong signal without background staining was obtained. Our results indicate that nonradioactive in situ hybridization could represent a useful tool for the detection of PRRSV in routinely fixed and processed tissues. In situ hybridization could also be used to differentiate infection by North American and European Lelystad-like PRRSV isolates. (+info)
Effect of dietary energy source and immunological challenge on growth performance and immunological variables in growing pigs.
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Forty-eight growing pigs (23 kg BW) were assigned to four treatments (n = 12) arranged as a 2 x 2 factorial. Dietary energy source (conventional [CON] vs high-oil corn [HOC]), with or without an immunological challenge (IC) regimen constituted main effects. The IC regimen consisted of injection of endotoxin (E. coli lipopolysaccharide [LPS]) and vaccination for porcine respiratory and reproductive syndrome (PRRS). Growth performance data were collected over a 5-wk period and are presented as prechallenge (d 1 to 14; d 1 was the 1st d of the study), challenge (d 15 to 21), and postchallenge (d 22 to 36) periods, and overall. Overall, the pigs fed HOC consumed less feed (P < .11) and gained more efficiently (P < .03). During the immunological challenge period, ADG was depressed 21% and feed intake 15% (P < .01). The IC resulted in lower (P < .01) serum alpha-1-acid glycoprotein (AGP) concentrations on d 22, and the magnitude of the reduction was greater in the pigs fed the CON diet (energy source x immune challenge, P < .10). Serum AGP concentrations remained lower (P < .08) in challenged pigs on d 36. Immunoreactive prostaglandin concentrations were higher (55%, P < .08) in the pigs fed HOC immediately following the IC period (d 22). The data reported herein indicate that the performance of pigs fed HOC is satisfactory, and that feeding HOC does not compromise growth performance during or after an immunological challenge. (+info)
Identification of the leader-body junctions for the viral subgenomic mRNAs and organization of the simian hemorrhagic fever virus genome: evidence for gene duplication during arterivirus evolution.
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Simian hemorrhagic fever virus (SHFV) was recently reclassified and assigned to the new virus family Arteriviridae. During replication, arteriviruses produce a 3' coterminal, nested set of subgenomic mRNAs (sgRNAs). These sgRNAs arise by discontinuous transcription, and each contains a 5' leader sequence which is joined to the body of the mRNA through a conserved junction sequence. Only the 5'-most open reading frame (ORF) is believed to be transcribed from each sgRNA. The SHFV genome encodes nine ORFs that are presumed to be expressed from sgRNAs. However, reverse transcription-PCR analysis with leader- and ORF-specific primers identified only eight sgRNA species. The consensus sequence 5'-UCNUUAACC-3' was identified as the junction motif. Our data suggest that sgRNA 2 may be bicistronic, expressing both ORF 2a and ORF 2b. SHFV encodes three more ORFs on its genome than the other arteriviruses. Comparative sequence analysis suggested that SHFV ORFs 2a, 2b, and 3 are related to ORFs 2 through 4 of the other arteriviruses. Evidence which suggests that SHFV ORFs 4 through 6 are related to ORFs 2a through 3 and may have resulted from a recombination event during virus evolution is presented. (+info)
A 68-nucleotide sequence within the 3' noncoding region of simian hemorrhagic fever virus negative-strand RNA binds to four MA104 cell proteins.
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The 3' noncoding region (NCR) of the negative-strand RNA [3'(-)NCR RNA] of the arterivirus simian hemorrhagic fever virus (SHFV) is 209 nucleotides (nt) in length. Since this 3' region, designated 3'(-)209, is the site of initiation of full-length positive-strand RNA and is the template for the synthesis of the 5' leader sequence, which is found on both full-length and subgenomic mRNAs, it is likely to contain cis-acting signals for RNA synthesis and to interact with cellular and viral proteins to form replication complexes. Gel mobility shift assays showed that cellular proteins in MA104 S100 cytoplasmic extracts formed two complexes with the SHFV 3'(-)209 RNA, and results from competition gel mobility shift assays demonstrated that these interactions were specific. Four proteins with molecular masses of 103, 86, 55, and 36 kDa were detected in UV-induced cross-linking assays, and three of these proteins (103, 55, and 36 kDa) were also detected by Northwestern blotting assays. Identical gel mobility shift and UV-induced cross-linking patterns were obtained with uninfected and SHFV-infected extracts, indicating that the four proteins detected are cellular, not viral, proteins. The binding sites for the four cellular proteins were mapped to the region between nt 117 and 184 (68-nt sequence) from the 3' end of the SHFV negative-strand RNA. This 68-nt sequence was predicted to form two stem-loops, SL4 and SL5. The 3'(-)NCR RNA of another arterivirus, lactate dehydrogenase-elevating virus C (LDV-C), competed with the SHFV 3'(-)209 RNA in competition gel mobility shift assays. UV-induced cross-linking assays showed that four MA104 cellular proteins with the same molecular masses as those that bind to the SHFV 3'(-)209 RNA also bind to the LDV-C 3'(-)NCR RNA and equine arteritis virus 3'(-)NCR RNA. However, each of these viral RNAs also bound to an additional MA104 protein. The binding sites for the MA104 cellular proteins were shown to be located in similar positions in the LDV-C 3'(-)NCR and SHFV 3'(-)209 RNAs. These data suggest that the binding sites for a set of the cellular proteins are conserved in all arterivirus RNAs and that these cell proteins may be utilized as components of viral replication complexes. (+info)