A monoclonal ELISA for bovine viral diarrhoea pestivirus antigen detection in persistently infected cattle

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.

A single amino acid is critical for the expression of B-cell epitopes on the helicase domain of the pestivirus NS3 protein

Truncated NS3 proteins, expressed by recombinant baculoviruses, were used to investigate the location of conserved B-cell epitopes on this non-structural bovine viral diarrhoea virus (BVDV) protein. A goat anti-pestivirus antiserum, and a panel of anti-NS3 monoclonal antibodies, including the BVDV-1 specific antibody P1D8, were used to verify the presence or absence of the epitopes. Interestingly, the monoclonal antibodies reacted only with the truncated protein encompassing the helicase domain of NS3. Expression of the B-cell epitopes was dependent on, but not within, a 57 amino acid sequence at the carboxy-terminal end of this protein, supporting observations that these conserved epitopes are conformational in nature. A comparison of deduced amino acid sequences of the helicase domain from BVDV-1, BVDV-2, BDV and CSFV isolates highlighted a single amino acid that appeared to be unique to P1D8-reactive BVDV-1 isolates. Site-directed mutagenesis studies confirmed that this amino acid is critical for the expression of the BVDV-1 specific NS3 epitope recognised by the P1D8 monoclonal antibody. Surprisingly, the amino acid was also important for an epitope recognised by two group-specific monoclonal antibodies, P1H11 and P4A11. Protein modelling studies, based on the structure of the hepatitis C NS3 helicase domain, indicated that this amino acid occupies a prominent position on the surface of the protein.

Evaluation of a new sandwich enzyme-linked immunosorbent assay for detection of bovine viral diarrhea virus in unprocessed fetal bovine serum

A new sandwich enzyme-linked immunosorbent assay (S-ELISA) kit that uses raw (unprocessed) fetal bovine serum (FBS) as the testing sample was evaluated for upstream bovine viral diarrhea virus (BVDV) testing. Pooled FBS samples (n = 84) were tested using the S-ELISA. Thirty serum samples originating from persistently infected (PI) calves that had been confirmed by virus isolation (VI) as BVDV positive and another 30 samples previously confirmed by VI as BVDV negative were also evaluated. Of the 84 field samples, the S-ELISA detected 13 (15.5%) BVDV-positive specimens. When these 13 positive samples were tested by VI and immunofluorescent assay, 11 (84.6%) were positive and 2 (15.4%) were negative. The S-ELISA was positive for all 30 PI samples (100%) and negative for all 30 negative samples (100%). These data indicate that the new kit is a relatively reliable diagnostic tool and can be considered for upstream detection of BVDV-contaminated raw FBS pools.

Evaluation of a new sandwich ELISA kit that uses serum for detection of cattle persistently infected with BVD virus

Cattle immunotolerant to and persistently infected (PI) with bovine viral diarrhea (BVD) virus (BVDV) constitute the mechanism by which BVDV persists in and spreads among cattle herds. Detection and elimination of PI cattle are necessary for control of BVD. Serum is an excellent specimen for BVD PI testing because of high survivability of BVDV in serum and ease of collection, storage, and handling. Currently, microtiter virus isolation (VI) employing serum and sandwich ELISAs (S-ELISA) on tissues or leukocytes are used for BVDV PI screening. This paper evaluates a new S-ELISA kit that uses serum as the diagnostic sample. Cattle sera (n = 408) were tested using VI and the S-ELISA. The VI detected 172 BVDV-positive sera. Of these, 18 were confirmed PI cattle. The S-ELISA was positive on all PI samples. Considering only the PI animals, and using VI as the gold standard, the relative sensitivity of S-ELISA was 100%. The overall relative sensitivity was 93.6% and the agreement quotient (kappa) was 0.94. The relative specificity of the kit, based on 236 VI-negative sera, was 100%. These data indicate that the new kit is very adequate for detection of BVDV PI cattle.

Laboratory diagnostic investigations for bovine viral diarrhoea virus infections in cattle

There are no pathognomonic clinical signs of infection with bovine viral diarrhoea virus (BVDV) in cattle. Diagnostic investigations therefore rely on laboratory-based detection of the virus, or of virus-induced antigens or antibodies in submitted samples. In unvaccinated dairy herds, serological testing of bulk milk is a convenient method for BVDV prevalence screening. Alternatively, serological testing of young stock may indicate if BVDV is present in a herd. In BVDV positive herds, animals persistently infected (PI) with BVDV can be identified by combined use of serological and virological tests for examination of blood samples. ELISAs have been used for rapid detection of both BVDV antibodies and antigens in blood, but should preferably be backed up by other methods such as virus neutralization, virus isolation in cell cultures or amplification of viral nucleic acid. Detailed knowledge of the performance of the diagnostic tests in use, as well as of the epidemiology of bovine virus diarrhoea is essential for identification of viremic animals in affected herds.

Evaluation of the suitability of a commercial bovine viral diarrhoea virus antigen capture ELISA for diagnostic testing

The suitability of a commercial bovine viral diarrhoea virus (BVDV) antigen capture enzyme-linked immunosorbent assay (ELISA) for routine diagnostic testing of bovine serum samples was evaluated by comparing the ELISA results of 214 sera with those obtained after two passages in roller tube cultures of fetal bovine lung cells and immunofluorescent staining using fluorescein isothiocyanate-conjugated hyperimmune BVDV anti-serum. In addition, 208 of these samples were tested by virus isolation in a microtitre system followed by indirect immunoperoxidase staining using a pool of two non-competing pestivirus specific monoclonal antibodies. The sensitivity of the ELISA compared with virus isolation followed by immunofluorescent and immunoperoxidase staining was 47.8 and 45.8%, respectively. The corresponding figures of specificity and overall correlation were 95.3 and 95.1%, and 90.2 and 89.4%. Twenty-two of 24 pestivirus isolates from the positive blood samples were typed as BVDV-like by monoclonal antibodies, indicating that the poor sensitivity of the ELISA was not due to the presence of atypical pestiviruses in the test sample. These results suggest that this ELISA is not suitable for testing blood samples for BVDV in a diagnostic laboratory.

Relationship between abortions and seroprevalences to selected infectious agents in dairy cows

The aim of this study was to determine whether the occurrence of abortion is related to the seroprevalence of abortion-causing infectious agents. In a cross-sectional study, cattle from dairy farms in Switzerland that were defined as having an abortion problem were divided into two groups: cows with a history of abortion within the previous 3 months (cases) and cows without a history of abortion (controls). A positive titre to Leptospira spp. was associated with an increased probability of being a case (OR = 1.74, 95% CI = 1.21-2.47). There were interactions between Coxiella burnetti titre and parity, and between Chlamydia psittaci and C. burnetti titre and breed. Multiparous cases after the second lactation with a positive titre to C. burnetti were less likely (OR = 0.42, 95% CI = 0.22-0.82) to be cases. Swiss Browns (Swiss Braunvieh and Brown Swiss) with a positive titre to C. psittaci and Swiss Browns with a positive titre to C. burnetti were more likely (OR = 1.63, 95% CI = 1.13-2.37 and OR = 1.79, 95% CI = 1.15-2.78, respectively) to be cases. Parity alone was not associated with the occurrence of abortion.

Microtiter virus isolation and enzyme immunoassays for detection of bovine viral diarrhea virus in cattle serum

Cattle immunotolerant to and persistently infected (PI) with bovine viral diarrhea (BVD) virus (BVDV) constitute the mechanism by which BVDV persists in cattle herds. Two procedures for using serum to detect PI cattle were developed and evaluated. BVDV was found to remain viable for 7 days in serum samples stored at room temperature. The tests use cell culture virus isolation (VI) in 96-well microtiter plates, followed by immunostaining of cell monolayers with monoclonal antibodies. One technique, the immunoperoxidase monolayer assay (IPMA), forms a red intracellular precipitate while the other, the monolayer enzyme-linked immunosorbent assay (M-ELISA) produces a yellow color in solution. The optimal incubation period for microtiter VI was determined to be 4 days. Optimal IPMA staining was obtained by fixing cell monolayers with 20 to 30% acetone, whereas a simple dry-rehydrate-dry cycle provided optimal M-ELISA staining. The M-ELISA and IPMA had the same sensitivities and specificities, but the M-ELISA was a more rapid procedure and use of a spectrophotometer for reading samples allowed for greater objectivity. When compared to standard VI with routine samples submitted for the diagnosis of BVD, M-ELISA and IPMA had a relative sensitivity of 85% and a relatively specificity of 100%. When only samples from cattle suspected of being PI were considered, these two parameters were 100% for both IPMA and M-ELISA. The two procedures, especially the M-ELISA, are suitable for whole-herd testing to identify PI cattle. The appeal of these tests is derived from the convenience of using serum as a diagnostic sample and the ability to rapidly screen large numbers of samples at low cost.

Antigenic differences among pestiviruses

Monoclonal antibody typing of pestiviruses, supplemented with genetic sequence comparisons, has shown that at least four antigenic clusters can be identified within the genus. One cluster represents "classic" bovine viral diarrhea strains, which also have been isolated occasionally from sheep and pigs, whereas a second group corresponds to classic swine fever (hog cholera) strains. A distinct group of "true" border disease isolates is found in sheep and has been isolated occasionally from swine. The fourth group is antigenically quite distinct form the others and has been isolated from sheep, pigs, and cattle. It includes recent American isolates from cases of acute severe hemorrhagic disease. The implications of these findings for diagnosis and control are discussed.

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.

Evaluation of an antigen-capture ELISA for detection of bovine viral diarrhea virus in cattle blood samples

From blood samples routinely received for bovine viral diarrhea (BVD) diagnosis, 860 samples without antibodies to BVD virus were examined in both virus isolation and in an antigen-detecting enzyme-linked immunosorbent assay (ELISA) based on monoclonal antibodies (MAbs) against the nonstructural BVD virus protein p125/p80. A total of 843 samples (98%) were positive (n = 170, 20%) or negative (n = 673, 78%) in both tests, corresponding to an agreement of kappa = 0.94. Among 17 samples with diverging results, 3 were from animals transiently infected with BVD virus, and 5 came from clinically affected animals. The reactivity of the MAbs was controlled against 387 field isolates of BVD virus. All were detected by the MAbs, thereby confirming the general view that the p125 virus protein is highly conserved among different BVD viruses.

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.

Epidemiological evaluation of a monoclonal ELISA detecting bovine viral diarrhoea pestivirus antigens in field blood samples of persistently infected cattle

An enzyme-linked immunosorbent assay (ELISA), using monoclonal antibodies for capture and detection, was developed for detecting bovine viral diarrhoea virus (BVDV) antigens in blood samples. The test was evaluated using 761 field samples of known status (viraemic or not). When an appropriate cut-off value was chosen, the sensitivity, specificity, and predictive values of the assay were 100%, higher than the values obtained by classical virus isolation. Correlation with the latter technique exceeded 90%. The ELISA is a good candidate for replacing virus isolation as a reference method for BVDV antigen detection in persistently infected carriers. A method based on the mean of the standard deviation ratio can be used to choose the cut-off value in order to optimise reproducibility.