Hybridization probes for the detection and differentiation of two serotypes of porcine rotavirus

A dot hybridization assay was developed to detect and differentiate two serotypes of porcine rotavirus by hybridization of specific probes to rotavirus RNA dotted onto nylon membranes. The assay was conducted using radiolabeled probes prepared from cDNA clones of OSU (serotype 5) and Gottfried (serotype 4) rotavirus gene 9 segments. The probes were prepared by excision of full length cDNA copies of gene 9 inserts from recombinant plasmids followed by nick translation and 32P-dCTP labeling. Rotavirus RNA samples used in the assay were prepared from tissue culture, and intestinal contents from gnotobiotic and conventional pigs. Optimal conditions for hybridization consisted of 52 degrees C, 50% formamide, and 5 x SSC. Hybridization studies with the OSU and Gottfried gene 9 probes have shown them to be specific with only low levels of cross-reactivity with heterologous rotavirus preparations. Sensitivity studies have demonstrated the ability of the probes to detect at least 2 ng of rotavirus RNA. Further development and refinement of this technique may provide a useful tool for the detection and differentiation of porcine rotavirus serotypes.     

Detection and differentiation of bovine group A rotavirus serotypes using polymerase chain reaction-generated probes to the VP7 gene.

Dot and Northern blot hybridization assays were developed to detect and differentiate group A bovine rotavirus serotypes using radiolabeled serotype 6 (Nebraska calf diarrhea virus [NCDV] and United Kingdom [UK] strains) or serotype 10 (Crocker [Cr] strain) VP7 gene probes. Partial length VP7-specific cDNA encompassing areas of major sequence diversity were generated by the polymerase chain reaction (PCR) using either cloned VP7 genes (NCDV and UK strains) or reverse transcribed mRNA (Cr strain) as templates. Radiolabeled probes prepared from the PCR-generated cDNA were tested at various stringency conditions to optimize the hybridization assays. At high stringency conditions (52 C, 50% formamide, 5 x standard saline citrate), the NCDV, UK, and Cr probes serotypically differentiated bovine rotavirus isolates in RNA samples prepared from cell culture propagated viruses or in fecal specimens from infected gnotobiotic calves. The sensitivity and specificity of NCDV and Cr VP7 probes were characterized in dot blot hybridization assays, and the probes were estimated to detect at least 1 ng of viral RNA. The serotyping results obtained using VP7 probes were similar to those obtained using serologic assays. Further development of these assays may provide a useful means for the rapid detection and differentiation of bovine rotavirus serotypes in fecal samples from calves in the field.     

Serotyping and antigenic comparison of some animal rotaviruses isolated in China.

Eight strains of rotaviruses isolated from diarrheal animals (4 from calves and 4 from piglets) in China were compared by serotyping with reference animal rotavirus strains (bovine NCDV, porcine OSU and simian SA-11 and human rotavirus Wa strain). Two-way cross neutralization test showed no antigenic difference between all 4 local strains of bovine rotavirus (BRV007, BRV014, HN-7 and BRV6555) and reference NCDV, so they belonged to rotavirus serotype 6 (bovine rotavirus serotype 1 or NCDV-serotype). Meanwhile, the four strains of Chinese porcine rotavirus could be determined into 2 different serotypes. One (Li99) was neutralised to a high titer with the antiserum against reference OSU virus and probably related to OSU (serotype 5 or porcine serotype 1). The other three strains (Lin71, Nan86 and Jiang150) were antigenically obviously different from Li99 and did not react with the antiserum against OSU. They were tentatively considered as porcine rotavirus serotype 2. All the strains of bovine and porcine rotavirus did not cross-neutralise with simian SA-11 and human Wa strain. There was also no antigenic relationship between bovine rotaviruses and porcine rotaviruses.     

Genetic heterogeneity of wild-type G4P[6] porcine rotavirus strains detected in a diarrhea outbreak in a regularly vaccinated pig herd

Group A rotavirus (RV-A) with short electropherotype was identified by ss-PAGE in a neonatal diarrhea outbreak at a Brazilian pig farm where the sows were regularly vaccinated with a commercial vaccine containing OSU (G5P[7]) and Gottfried (G4P[6]) porcine RV-A (PoRV-A) strains. The ss-PAGE positive stool samples (n=20) were characterized as P[6] genotype by multiplex-nested-RT-PCR assay. The nucleotide analysis of the VP4 gene (VP8*) state that the viruses clustered in P[6] lineages that are also shared by RV-A strains identified in human hosts. Nucleotide analysis of the VP7 gene identified different lineages in G4 including a new lineage tentatively designated IX. The immunological pressure induced by commercial vaccine with a rotavirus containing a G4P[6] genotype of porcine origin (Gottfried strain) might have allowed the selection of PoRV-A strains with characteristics found in RV-A strains isolated of human hosts, such as P[6]-Ie and If, and promoted the selection or emergence of RV-A strains with a new lineage of the G4 genotype. The characterization of PoRV-A strains with unusual genotypes described in this study highlight the importance of surveys on the relationship between human and animal rotavirus strains.     

Development of hybridization probes on the basis of recombinant DNA to identify porcine parvoviruses and rotaviruses

Porcine parvovirus (PPV) and porcine rotavirus (PRV) infections can be diagnosed, and the diagnosis greatly contributes to their control. For the diagnosis of PPV and PRV of pigs recombinant DNA were obtained which could be used as hybridization probes. Homology between PPV-RNA and cloned cDNA was confirmed, and the ability of plasmid probes to detect PRV was demonstrated. Hybridization with preparations of both PPV-infected cells and purified PPV gave positive reproducible results. The results are useful as an experience for the development of a sandwich hybridization system for PPV detection.     

Distinct serotypes of porcine rotavirus associated with diarrhea in suckling piglets in southern Quebec.

Cytopathic rotavirus strains were isolated in cell cultures from the intestinal contents of diarrheic piglets on Quebec pig farms where repeated outbreaks of enteritis occurred. All the isolates shared the common group antigens of rotaviruses as revealed by immunofluorescence and counterimmunoelectrophoresis. A hemagglutinating activity was demonstrated with human group O, porcine and guinea pig erythrocytes. At least one of the isolates was clearly distinguished from the American prototype of porcine rotavirus (strain OSU) by neutralization and hemagglutination inhibition tests; a third serotype was also suspected. By polyacrylamide gel electrophoresis of RNA, it was not possible to differentiate these isolates.     

The use of biotin-labeled cDNA probes for the detection of infectious bursal disease viruses

A cDNA library was prepared from the double-stranded RNA genome of the infectious bursal disease virus (IBDV) strain ST-C. The cDNA molecules were annealed into the plasmid pUC9 and used to transform Escherichia coli strain JM107. A cDNA clone that contained IBDV-specific nucleotide sequences was selected and designated STC-1. Radiolabeled probes were prepared from STC-1 and hybridized to genome segment A of ST-C in a northern blot hybridization assay. The STC-1 cDNA was 448 base pairs in length, and its nucleotide sequence indicated that it is located near the VP-2/VP-4 junction in IBDV genome segment A. Biotin-labeled probes were prepared from STC-1 and used in a dot-blot hybridization assay to detect IBDV. Under relatively low stringency conditions of hybridization, the biotinylated probes detected four subtypes of IBDV serotype 1 and a serotype 2 IBDV isolate.     

Serotypes and intimin types of intestinal and faecal strains of eae+ Escherichia coli from weaned pigs

Enteropathogenic Escherichia coli (EPEC) that are known to cause severe diarrhoea in children and young rabbits are well characterized, but there are few reports on the serotypes and intimin (eae) types of EPEC in weaned pigs. Based on detection of the eae gene by PCR and by DNA-hybridisation with LEE specific gene probes, 20 intestinal and 17 faecal eae(+) strains from diarrhoeal (164) and non-diarrhoeal (57) weaned pigs from 13 Hungarian farms, representing 12.8% of diarrhoeal and 14.0% of non-diarrhoeal pigs, were identified. The dominant serotype was O123:H11 (40%) among intestinal, and O108:H9 (23%) among faecal strains. The majority (85%) of the intestinal strains possessed eae-beta and 10% carried eae-gamma gene. In contrast, significantly (p<0.025) fewer faecal strains (53%) harboured the eae-beta gene, and 23% were eae-gamma positive. In vitro adhesion tests of intestinal and faecal eae(+) strains indicated adhesion of 20/37 of the strains to PK15 (porcine kidney) cells while only 3/37 strains adhered to HeLa cells. The ultrastructure of intimate bacterial attachment of representative porcine eae(+) strains to PK15 cells showed no pedestal formation, in contrast to the human EPEC (O127:H5, eae-alpha) strain. In conclusion, the data do not demonstrate a significant role for the eae(+)E. coli in porcine post-weaning diarrhoea, but provide new information on a dominant porcine serotype (O123:H11, eae-beta), and on differences of serotypes and intimin types of porcine eae(+) strains according to their site of isolation. Furthermore there was an indication that the PK15 cell line could be used as a model to study in vitro adherence of eae(+)E. coli of some human and porcine origin.     

Characterization of infectious bronchitis virus isolates by slot blot hybridization

We used slot blot hybridization of the hypervariable regions of the S1 subunit of spike peplomer gene to identify and characterize infectious bronchitis virus (IBV) strains. Template DNA was created from six reference strain IBVs of different serotypes and immobilized on a nitrocellulose membrane. We synthesized digoxigenin-labeled probes from reference and unknown field viruses and hybridized them to template DNA. All reference strains could be distinguished and isolates identified by serotype if they were at least 95% identical to a reference strain. This slot blot hybridization procedure was specific and reproducible, and strain typing was consistent with the S1 sequencing of the IBV genome. This study thus provides a simple and rapid method for typing of IBV.     

A群猪轮状病毒JS株vp7基因序列分析

根据已发表的猪轮状病毒OSU毒株vp7基因核苷酸序列ORF两端保守区序列,设计一对特异引物,以猪轮状病毒JS毒株反转录cDNA为模板,通过PCR方法扩增出长约1000 bp目的片段。将其进行T-A克隆、序列测定和分析。结果表明,vp7基因全长1062 bp,含有一个981 bp的开放阅读框,编码326个氨基酸。与已知的15个毒株vp7全长基因的核苷酸及推导的氨基酸序列比较,同源性分别为74.5%～78.5%和75.2%～83.1%,核苷酸系统发育进化树结果表明,JS毒株与轮状病毒G9型参考毒株ICB2185、O-1亲缘关系较近,分为一个群,表明JS毒株血清型为G9型。目前,我国尚未见猪及其它动物轮状病毒G9型流行株的报道。     

猪链球菌PCR检测技术研究进展

猪链球菌是猪的一种重要病原菌,并且也会引起人的链球菌病。有35个荚膜血清型(1/21、~34),通常自发病或死亡猪体分离获得1,2,7,9型和14型菌株,其中2型是毒力最强的血清型。根据已知猪链球菌16 SrRNA及溶血素(sly)、谷氨酸脱氢酶(gdh)、荚膜多糖(cps)、胞壁蛋白或溶菌酶释放相关蛋白(mrp)、胞外因子(epf)编码基因序列设计特异性引物,建立猪链球菌群和1(14),2(1/2),7型和9型特异性PCR或多重PCR,建立2型致病性菌株和1型高致病性菌株毒力鉴定PCR或多重PCR,用于检测和鉴别临床病料和细菌分离物中的猪链球菌,具有高敏感性和高特异性,与其他致病菌及其他血清的猪链球菌型无交叉反应,为疫病诊断及流行病学的研究提供了快速、简便和有用的工具。     

Prevalence of antibodies to four bovine rotavirus strains in different age groups of cattle

Neutralizing antibody titers to four bovine rotavirus strains, representing three serotypes, were measured in 160 sera from cattle of different age groups. Age-specific seroprevalence analysis revealed serotype 6, represented by bovine rotavirus (BRV) NCDV, as the predominant rotavirus serotype infecting German cattle and serotype 10, represented by BRV V1005, as the least prominent. Infections with serotype 8, represented by BRV 678, occurred with intermediate frequency. Antibodies of young calves distinguished between NCDV and UK virus, two serotype 6 BRV strains differing in VP4 antigen.     

Detection of porcine parvovirus using nonradioactive nucleic acid hybridization

Nonradioactive slot blot hybridization assays were established for the detection of porcine parvovirus (PPV), using either a digoxigenin-labeled DNA probe or a biotinylated RNA probe. All probes were prepared from a 3.3-kb Pst1-EcoR1 DNA fragment of the NADL8 isolate of PPV. The sensitivity and specificity of the probes in a slot blot system were evaluated in comparison with a 32P-radiolabeled RNA probe. Using an anti-digoxigenin alkaline phosphatase detection system, at least 1 ng of viral replicative form (RF) DNA, or the equivalent of 100 plaque forming units (PFU) of infectious virus, could be detected by the digoxigenin-labeled DNA probe. When the biotinylated RNA probe and a strepavidin-alkaline phosphatase detection system were employed, 0.1 ng of RF DNA, or the equivalent of 10 PFU of infectious virus, were detected, comparable to the sensitivity of the 32P-radiolabeled RNA probe. Hybridization was not observed with control DNA samples extracted from swine testicle cells, porcine kidney (PK-15) cells, uninfected mixed swine fetal tissue, or from an unrelated DNA virus (pseudorabies virus) infected PK-15 cells. Different isolates of PPV, namely NADL8, NADL2, KBSH, and Kresse, reacted on an equimolar basis in sensitivity and specificity to the biotinlyated probe. Extraction of DNA directly on the filter membrane (direct filter hybridization) was employed in an attempt to reduce processing time by eliminating DNA extraction steps. Direct filter hybridization was indeed less time consuming; it was also comparable in sensitivity and specificity to those methods employing purified DNA.     

猪轮状病毒GD1株VP7基因的克隆及序列分析

参考GenBank中发表的PRV OSU毒株VP7基因核苷酸序列ORF两端保守区序列,设计1对特异引物,以PRV GD1株反转录cDNA为模板,通过PCR方法扩增出长约1 kb的基因片段,并克隆到pMD18-T载体中进行序列测定。测序结果表明:VP7基因全长1 062 bp,含有一个981 bp的开放阅读框,编码326个氨基酸。与国内外已知的13个毒株VP7全长基因的核苷酸及推导的氨基酸序列比较,相似性分别为77.4%～100%和78.6%～99.7%;核苷酸系统发育进化树结果表明,GD1毒株与轮状病毒A2,JP3-6毒株亲缘关系较近,为一个进化群。     

An Actinobacillus pleuropneumoniae PCR typing system based on the apx and omlA genes--evaluation of isolates from lungs and tonsils of pigs

The genetic variability of a gene coding for an outer membrane lipoprotein (omlA) was used to develop a PCR typing system for Actinobacillus pleuropneumoniae. Sequence differences in the middle region of the gene divided the A. pleuropneumoniae serotypes in five distinct groups. Group I included serotypes 1, 9, 11 and 12 (omlA l), Group II consisted of serotypes 2 and 8 (omlA II), Group III included serotypes 3, 6 and 7 (omlA III), Group IV (omlA IV) consisted of serotype 4 and Group V of serotypes 5a, 5b and 10 (omlA V). The sequence differences were utilized to construct PCR primers specific for each group, except of Group IV, as the amplicon of serotype 4 could be separated from Group III by size. Together with a PCR apx typing system, the omlA PCR typing system could discriminate the majority of A. pleuropneumoniae serotypes of biovar 1 except of serotypes 1, 9 and 11 and serotypes 2 and 8. The PCR typing system was tested on 102 field strains of A. pleuropneumoniae isolated from lungs of diseased pigs. The serotyping results of the investigated field strains were in agreement with the apx and omlA gene patterns found in the reference strains of the bacteria, with the exception of the omlA gene of five strains of serotype 8. To examine the apx and omlA gene pattern of tonsil isolates, the PCR typing system was tested on a total of 280 A. pleuropneumoniae field strains isolated from tonsils of pigs. Agreement between serotyping and DNA typing was found in 96% of the isolates using the apx gene patterns and in 89% of the isolates using the omlA gene. The same serotype specific apx/omlA gene pattern was thus found in the majority of the tonsil isolates and in isolates from diseased lungs. Most of the differences in the omlA gene were found in 18 tonsil isolates of serotype 12. The omlA/apx PCR typing system described in the present study makes it possible to determine the type specificity of the majority of A. pleuropneumoniae isolates by simple PCR technique and enables phenotype independent characterization of isolates non-typable by serotyping.     

In situ hybridization for the detection of the apxIV gene in the lungs of pigs experimentally infected with twelve Actinobacillus pleuropneumoniae serotypes

The detection of the apxlV gene in lung tissues from pigs experimentally infected with the 12 major A. pleuropneumoniae serotype (1 to 12) reference strains was studied by in situ hybridization using a non-radioactive digoxigenin-labeled DNA probe. In situ hybridization produced a distinct positive signal in all pigs inoculated with the 12 A. pleuropneumoniae serotypes. Positive hybridization typically exhibited a dark-brown to black reaction product in intracellular and extracellular locations, without background staining. A strong hybridization signal was seen in degenerated alveolar leukocytes ("oat cells") adjacent to the foci of coagulative necrosis and in the alveolar spaces. The in situ hybridization methodology developed for the detection of the apxIV gene is a valuable tool for the diagnosis of porcine pleuropneumonia caused by A. pleuropneumoniae when only formalin-fixed tissues are submitted for diagnosis.     

Comparative virulence of two porcine group-A rotavirus isolates in gnotobiotic pigs

The virulence of 2 porcine group-A rotavirus isolates was compared. Forty hysterotomy-derived 3-day-old gnotobiotic pigs were inoculated orally with 2 ml of intestinal homogenate containing either the Ohio State University (OSU) or the South Dakota State University (SDSU) strain of porcine rotavirus or were inoculated with medium only. Clinical signs of disease, body weight, distribution of viral antigen, fecal excretion of virus, and histologic lesions (observed by light and scanning electron microscopy) were determined. Morphometric measurements of villi and crypts were made. In pigs inoculated with OSU or SDSU strains, diarrhea began at postinoculation hours (PIH) 19 to 48 and PIH 24 to 54, respectively. None of the virus-infected pigs died as a consequence of infection and all had similar clinical signs of disease, body weight changes, and virus-shedding patterns, regardless of the strain of rotavirus with which they were infected. Microscopic findings in the small intestine of virus-infected pigs were similar, except that the SDSU strain caused more severe villus atrophy and villus fusion in the duodenum at PIH 72 and 168 than was associated with the OSU strain. Viral antigen in the small intestine of pigs infected with either virus was observed by use of immunofluorescence at PIH 24 and 72, but was seldom seen at PIH 168.     

Relative prevalence of typical and atypical strains among rotaviruses from diarrheic pigs in conventional swine herds

Polyacrylamide gel electrophoresis was conducted on genomic RNA extracted from rotaviruses detected in diarrheic pigs from conventional swine herds. Ninety samples contained sufficient virus for RNA band visualization and genome classification. Genome profiles were characteristic of typical group A rotaviruses in 67.8% of the 90 samples, of group B rotaviruses in 10.0%, and of group C rotaviruses in 11.1%. In 11.1% of the samples, the presence of more than 11 bands suggested concurrent infection with more than 1 strain of rotavirus. In infections among nursing pigs, 76.4% were group A rotaviruses, 7.4% were group B, 7.4% were group C, and 8.8% were coinfections. In infections among weaned pigs, 40.9% were group A, 18.2% were group B, 22.7% were group C, and 18.2% were coinfections. Coelectrophoresis with prototype OSU and Gottfried strains revealed a great diversity in electropherotype among field strains of rotavirus.