Detection of BVD viruses using synthetic oligonucleotides

Laboratory diagnosis of bovine viral diarrhea virus infections

The past 20 years have witnessed dramatic improvements in laboratory methods for diagnosing bovine viral diarrhea virus(BVDV) infections. However, improvements in diagnostic technology have not necessarily led to improved diagnosis of BVDV at the individual animal or herd level. This article reviews BVDV laboratory diagnostic methods in the context of their rational application for improved detection of BVDV in the field.

Improved antigen and nucleic acid detection in a bovine virus diarrhoea eradication program

A bovine viral diarrhoea/mucosal disease (BVD/MD) control and eradication program was introduced in Lower Austria in 1996, according to the Swedish model. An important risk factor for BVD transmission under local conditions is communal grazing where susceptible pregnant cattle from several herds may be mixed with unrecognised persistently infected (PI) animals. A reliable system for identification of PI animals is therefore essential for BVD eradication and steps were taken to improve a commercially available antigen-capture ELISA (Ag-ELISA) by modifying the method for leukocyte preparation and adjusting the negative cut-off value. A single-tube reverse transcriptase-polymerase chain reaction (RT-PCR) employing panpestivirus 324/326 primers targeting the 5'-untranslated region of the virus genome was also simplified and used on pooled blood samples to facilitate larger sample throughputs. RT-PCR positive pools were analysed individually to identify infected animals. Seven hundred eighty-six samples were tested by Ag-ELISA according to the instruction manual and 5324 samples with the modified method. All 6110 samples were retested by RT-PCR. The percentage of RT-PCR positive results with doubtful and negative Ag-ELISA samples significantly diminished using the modified method (from 4.71 to 0.82%). Selected BVD viruses were genetically typed by PCR product sequencing; special attention being paid to RT-PCR amplicons from samples which were negative or doubtful by ELISA. However, no correlation was found between the phylogenetic grouping of the viruses and the Ag-ELISA results.

Genetic heterogeneity of bovine viral diarrhoea viruses isolated in Southern Africa

Seventy three field isolates of bovine viral diarrhoea virus (BVDV), obtained from cattle in Mozambique and South Africa, were characterised by comparative nucleotide sequence analysis of part of the 5' non-coding region (5'NCR) of the viral genome. The target region was amplified by reverse transcription-polymerase chain reaction (RT-PCR). The amplicons were cloned in pUC 19 plasmid and both strands were sequenced by T7 polymerase dideoxynucleotide chain-termination sequencing or directly by cycle sequencing. The 245 base pair (bp) nucleotide sequences, derived from the 5'NCR, were aligned and compared to the corresponding positions of published sequences of BVDV type I and II strains and of pestiviruses of ovine and porcine origin. The phylogenetic trees, generated from those comparisons, allowed the Southern African isolates to be assigned to two main groups within the BVDV I genotype. Group A could be subdivided into three clusters, two of which grouped with BVDV strains of European and American origin. The third cluster did not group with any known BVDV I strains and it was confirmed in a comparison from the NS3 coding region. Group B contained more divergent isolates which differed by 18-23%, from BVDV I reference strains NADL, Osloss and SD-1 and comprised another distinct subset within the BVDV I genotype. This grouping was consistent in a comparison involving the NS2-NS3 region. It was concluded that BVD viruses occurring in Southern Africa are genetically diverse, comprising different variants within the BVDV I genotype. They include viruses similar to BVDVs found in Europe and America and others apparently rare or absent in those continents, termed here as BVDV Ic and Id. The co-existence of BVDV strains of European and American origin in certain areas both in Mozambique and South Africa, indicates a probable introduction of those viruses through imports of cattle or through potentially infectious bovine products. In addition, the detection of isolates apparently rare or absent from Europe and America may indicate the presence of African variants of BVDV I (Pestivirus 1).

In-vitro cell culture models of the nasal epithelium: a comparative histochemical investigation of their suitability for drug transport studies

PURPOSE

To evaluate different in-vitro cell culture models for their suitability to study drug transport through cell monolayers.

METHODS

Bovine turbinate cells (BT; ATCC CRL 1390), human nasal septum tumor cells (RPMI, 2650; ATCC CCL 30), and primary cell cultures of human nasal epithelium were characterized morphologically and histochemically by their lectin binding properties. The development of tight junctions in culture was monitored by actin staining and transepithelial electrical resistance measurements.

RESULTS

The binding pattern of thin-sections of excised human nasal respiratory epithelium was characterized using a pannel of fluorescently-labelled lectins. Mucus in goblet cells was stained by PNA, WGA and SBA, demonstrating the presence of terminal N-acetylglucosamine, N-acetylgalactosamine and galactose residues respectively in the mucus of human nasal cells. Ciliated cells revealed binding sites for N-acetylglucosamine, stained by WGA, whereas Con A, characteristic for mannose moieties, labelled the apical cytoplasm of epithelial cells. Binding sites for DBA were not present in this tissue. Comparing three different cell culture models: BT, RPMI 2650, and human nasal cells in primary culture using three lectins (PNA, WGA, Con A) as well as intracellular actin staining and transepithelial electrical resistance measurements we found, that only human nasal epithelial cells in primary culture showed differentiated epithelial cells, ciliated nasal cells and mucus producing goblet cells, which developed confluent cell monolayers with tight junctions.

CONCLUSIONS

Of the in-vitro cell culture models studied, only human nasal cells in primary culture appears to be suitable for drug transport studies.

Diagnosis of bovine viral diarrhea virus infections

Because of complex pathogenesis and insidious nature of BVDV infections, the laboratory diagnosis is an essential component of developing measures for the control and prevention of BVDV infections. The positive isolation of BVDV from animal submissions or from aborted fetuses should provide a strong indication for further epidemiologic investigations within the identified infected herds. In these situations, the ultimate goal should be the establishment of sound control and prevention methods by prevention of any potential exposure to BVDV (i.e., removal of PI animals and preventing the introduction of infected animals) and by protecting animals by using effective vaccination programs.

Diagnosis of naturally occurring bovine viral diarrhea virus infections in ruminants using monoclonal antibody-based immunohistochemistry

Formalin-fixed paraffin-embedded tissues from 50 spontaneous cases (39 bovine, nine ovine, two caprine) of bovine viral diarrhea virus (BVDV) infection diagnosed by virus isolation were retrospectively examined for BVDV antigen by immunohistochemistry using anti-BVDV gp-43 monoclonal antibody (Mab 15C5). The cases were separated into enteric disease syndrome, respiratory disease syndrome, and abortion/weak calf syndrome based upon clinical disease. The purposes of the study were to 1) compare routine virus isolation with immunohistochemistry in determining BVDV infection and 2) define tissue and cellular distribution of BVDV in various clinical manifestations of infection. In bovids, there was 100% concordance of virus isolation and immunohistochemistry using Mab 15C5 in cases of enteric disease (mucosal disease, acute and chronic diarrhea, neonatal diarrhea), respiratory disease, and abortion. When laboratory tests were restricted to gastrointestinal tissue and/or feces, virus isolation detected BVDV in only 65% of cattle, whereas immunohistochemistry detected BVDV antigen in 100% of cattle. Immunohistochemical detection of pestivirus was poor in cases of ovine abortion, ovine hairy shaker syndrome, and caprine abortion. The tissue distribution of BVDV antigen was widespread in individual cattle with all clinical forms of BVDV infection. Viral antigen accumulation was spatially correlated with tissue lesions (in the absence of other pathogens) only in the gastrointestinal tract, lymphoid tissue, lung, placenta, and eye. This study demonstrates the utility of immunohistochemistry using Mab 15C5 to diagnose BVDV infections in cattle with a broad spectrum of clinical disease.

Ruminant pestiviruses

The ruminant pestiviruses, bovine virus diarrhoea virus (BVDV) and border disease virus (BDV) are highly successful and important pathogens which infect ruminant species worldwide. Although the serological relationships among ruminant pestiviruses require further clarification, there is growing evidence for two antigenic groups, one of which predominates in cattle and one in sheep. The success of pestiviruses stems from the ability of the non-cytopathic (NCP) biotype of the virus to cross the placenta and establish a persistent infection (PI) in the developing foetus. This biotype should be regarded as the 'normal' biotype with the cytopathic (CP) biotype being an abnormal virus that is usually isolated only from PI animals dying from mucosal disease. Recent molecular evidence points to CP viruses arising from their NCP counterparts by recombination events that include the insertion of host RNA and/or the duplication of viral RNA sequences. However, the biological mechanism through which CP viruses kill cells remains unknown. Virtually all CP and NCP viruses cause only mild, transient clinical symptoms in healthy adult animals and stimulate a protective immune response. Despite the urgent requirement for a safe, effective vaccine, there is still no commercial vaccine that has been shown to immunize dams so that foetal infection is prevented. In the absence of an effective vaccine, reliable diagnostic techniques are essential to implement effective control measures. There is now a range of monoclonal antibody-based enzyme-linked immunosorbent assays for identifying PI or convalescent animals. These tests are specific, rapid, sensitive and reliable but may themselves become redundant as they are superceded by ever-increasing molecular biology-based techniques.

Special tests for the diagnosis of infectious causes of reproductive failure in ruminants

The detection of many infectious disease agents, including those of importance in ruminant reproductive failure, increasingly will be achieved through means other than the laborious and time-consuming traditional isolation and culture procedures. New diagnostic methodologies are designed both to enhance the rapidity with which results are obtained and to increase specificity and sensitivity of identification of the causative agent. Immunoenzyme histochemical staining of formalin-fixed paraffin-embedded tissues offers, especially in cases of abortions in which necropsy material routinely is examined histologically, an efficient and timely means of identifying many important pathogens. Antemortem serologic diagnostics will continue to be dominated by ELISA technologies. In the past decade, the specificity of serodiagnosis has been enhanced greatly by the use of monoclonal antibody-based competitive ELISA systems and further improvements in such methods will result from the use of defined antigens derived by recombinant DNA techniques. Although DNA hybridization technology has been applied successfully to detect many important veterinary pathogens and has been shown to have merit for improved diagnosis of some fastidious agents, those methods, because of their technical complexity, in general, have not been shown to be applicable for routine diagnostic uses. In contrast, methods using the PCR for specific gene amplification offer exceptional promise. Although the PCR presently is too technically exacting for routine use, its broad applicability and exquisite sensitivity and specificity suggest that it will play an ever-increasing role in future veterinary diagnostic techniques.

Evaluation of PCR for diagnosis of bovine viral diarrhea virus in tissue homogenates

Tissue homogenates from 60 specimens submitted to the Veterinary Diagnostic Center were evaluated by polymerase chain reaction (PCR) for detection of bovine viral diarrhea virus (BVDV). Conventional virus isolation procedures showed the specimens contained BVDV. The BVDV RNA was extracted from the homogenates and subjected to a reverse transcription reaction followed by PCR amplification. The PCR product was blotted onto a nylon membrane and hybridized with a 30-base pair oligonucleotide probe labeled with 32P. One set of PCR primers detected BVDV in 46/60 (77%) of the tissue homogenates. An additional set of primers was used to detect 10/11 samples that had escaped detection with the first set of primers. The results indicate that BVDV can be detected by PCR directly out of tissue homogenates generated in a diagnostic setting.

Comparative hybridization and nucleotide sequence information from two noncytopathic isolates of bovine viral diarrhea virus

Comparative hybridizations of 8 cytopathic (CP) and 11 noncytopathic (NCP) isolates of bovine viral diarrhea virus (BVDV) were done using 4 different cDNA hybridization probes. The hybridization probes were prepared from cDNA synthesized from 1 CP BVDV (NADL) and 2 NCP BVDV isolates (SD-1 and NY-1) within the p80 region and from cDNA spanning the 5' untranslated region of NCP SD-1. Hybridization with the 5'/SD-1 probe detected 19 out of 19 isolates, whereas the p80/NADL, p80/NY-1 and p80/SD-1 hybridization probes detected only 12, 16 and 13 isolates, respectively. To determine the basis for the different patterns of hybridization, the nucleotide sequence was determined for the p80/NY-1. The nucleotide sequence was compared with the published CP NADL and CP Osloss and NCP SD-1 and NCP1 nucleotide sequences and in 45% of the base differences between NY-1 and NADL, NY-1 and Osloss were divergent from NADL, SD-1 and NCP1. Based on comparative nucleotide sequence data and the different reactivities of the p80/NADL, p80/NY-1 and p80/SD-1 hybridization probes the relationships of the various test isolates were characterized.

Comparison of nucleic acid hybridization and nucleic acid amplification using conserved sequences from the 5' noncoding region for detection of bovine viral diarrhea virus

Primers and probes derived from conserved sequences located in the 5' noncoding region of pestiviruses were evaluated for detection of bovine viral diarrhea virus. With these reagents, hybridization and polymerase chain reaction tests detected 62 of 90 and 90 of 90 bovine viral diarrhea virus isolates, respectively. A quick lysis method for preparing RNA for use in polymerase chain reaction amplification also was evaluated.

Presumptive diagnostic differentiation of hog cholera virus from bovine viral diarrhea and border disease viruses by using a cDNA nested-amplification approach

Hog cholera virus (HCV), bovine viral diarrhea virus (BVDV), and border disease virus (BDV) are closely related pestiviruses. BVDV and BDV are found worldwide but seldom cause disease in swine. In contrast, HCV has been successfully eradicated from swine in several nations but poses a potentially devastating threat to them because of its great virulence. Rapid differential diagnosis of HCV from BVDV and BDV infections in swine is vital for detection of the possible reintroduction of HCV into national herds from which it has been eradicated. Nested polymerase chain reactions (PCRs) for each of two pestiviral genomic segments are described. Amplification of the relatively conserved 5' genomic terminus identified 59 of 61 HCV, BVDV, and BDV isolates generically as pestiviruses. Nested amplification of the second region was designed to differentiate HCV from BVDV and BDV by exploiting relatively conserved differences in the nucleotide sequences that encode the major envelope glycoprotein. This second PCR correctly identified 36 of 36 diverse HCV isolates while failing to recognize any of 25 BVDV and BDV isolates. Multiple restriction fragment length analyses confirmed the identities of both external and nested PCR products. The two sets of PCRs may help confirm the generic identity of most pestiviruses and may permit presumptive differential diagnosis of HCV from BVDV and BDV.

Genetic diversity and BVD virus

The various measures of genetic variation of BVD virus was reviewed with emphasis on the implications for future control of virus-induced disease and diagnosis. While experimental data does not support unique serotypes for BVDV, there is substantial antigenic variation among the isolates examined. This variation may permit fetal infections even in animals assumed to be well vaccinated. The genetic differences between cytopathic and noncytopathic strains of BVDV are expressed in infected cells by the production of a p80 protein by cytopathic strains. In addition, cellular gene inserts have been detected in cytopathic strains. Monoclonal antibodies have demonstrated a high degree of diversity with the pestivirus population. Grouping of BVDV isolates by monoclonal antibody analysis is suggestive at best. The use of nucleic acid probes as diagnostic reagents has been compromised by the nucleic acid sequence variation found in the BVDV isolates tested.

Hybridization analysis of genomic variability among isolates of bovine viral diarrhoea virus using cDNA probes

Genomic variability among 28 cytopathic and 37 non-cytopathic isolates of BVDV was evaluated using hybridization analysis. Total RNA, isolated from cell cultures infected with BVDV, was probed with each of three plasmids containing cDNA derived from the cytopathic BVDV-NADL isolate. The three cDNA plasmid probes represented about 40% of the BVDV-NADL genome. The probes originated from the 5' end of the viral genome, the region of the genome coding for the p80 polypeptide and the 3' end of the genome. Three temperatures, 63 degrees C, 53 degrees C and 43 degrees C, were used for hybridization and washing and allowed approximately 29%, 36%, and 43% mismatch, respectively. Fifteen of the BVD viral isolates differed by less than 29% from BVDV-NADL in all three of the regions probed. Seventeen of the BVD viral isolates differed between 36% and 43% from BVDV-NADL in all three of the regions probed. Ten viral isolates differed by more than 43% from BVDV-NADL in all the regions probed. The remaining viral isolates exhibited different levels of similarity to BVDV-NADL in the three areas probed.