Function of bovine CD46 as a cellular receptor for bovine viral diarrhea virus is determined by complement control protein 1

The pestivirus bovine viral diarrhea virus (BVDV) was shown to bind to the bovine CD46 molecule, which subsequently promotes entry of the virus. To assess the receptor usage of BVDV type 1 (BVDV-1) and BVDV-2, 30 BVDV isolates including clinical samples were assayed for their sensitivity to anti-CD46 antibodies. With a single exception the infectivity of all tested strains of BVDV-1 and BVDV-2 was inhibited by anti-CD46 antibodies, which indicates the general usage of CD46 as a BVDV receptor. Molecular analysis of the interaction between CD46 and the BVD virion was performed by mapping the virus binding site on the CD46 molecule. Single complement control protein modules (CCPs) within the bovine CD46 were either deleted or replaced by analogous CCPs of porcine CD46, which does not bind BVDV. While the epitopes recognized by anti-CD46 monoclonal antibodies which block BVDV infection were attributed to CCP1 and CCP2, in functional assays only CCP1 turned out to be essential for BVDV binding and infection. Within CCP1 two short peptides on antiparallel beta strands were identified as crucial for the binding of BVDV. Exchanges of these two peptide sequences were sufficient for a loss of function in bovine CD46 as well as a gain of function in porcine CD46. Determination of the size constraints of CD46 revealed that a minimum length of four CCPs is essential for receptor function. An increase of the distance between the virus binding domain and the plasma membrane by insertion of one to six CCPs of bovine C4 binding protein exhibited only a minor influence on susceptibility to BVDV.     

Isolation of bovine herpesvirus-1 (BHV-1) and bovine viral diarrhea virus (BVDV) in association with the in vitro production of bovine embryos

The purpose of this study was to determine whether oocytes obtained from bovine ovaries collected at commercial abattoirs for use in in vitro fertilization programs would be contaminated with bovine herpesvirus-1 (BHV-1) and/or bovine viral diarrhea virus (BVDV). In total, of 85 samples tested containing 759 embryos produced by in vitro fertilization, 2 (2.4%) were positive for BHV-1 while none were positive for BVDV. The follicular fluid collected during oocyte aspiration tested positive in 11.8% for BVH-1 and in 4.7% for BVDV. Oviductal cells used to co-culture zygotes/embryos tested positive for BHV-1 and BVDV in 6.2% and 1.2% samples respectively.     

Role of the low-density lipoprotein receptor in entry of bovine viral diarrhea virus

Among several proposed cellular receptors for bovine viral diarrhea virus (BVDV), the low-density lipoprotein (LDL) receptor is of special interest because it is also considered a receptor for the related hepatitis C virus. It has been reported that an anti-LDL receptor monoclonal antibody blocked the infection of bovine cells by BVDV and that the resistance of bovine CRIB cells (cells resistant to infection with BVDV) (E. F. Flores and R. O. Donis, Virology 208:565-575, 1995) to BVDV infection was due to a lack of the LDL receptor (V. Agnello et al., Proc. Natl. Acad. Sci. USA 96:12766-12771, 1999). In connection with our studies on BVDV entry, we reevaluated the putative role of the LDL receptor as a cellular receptor for BVDV. It was first clearly demonstrated that neither of two monoclonal antibodies against the LDL receptor inhibited BVDV infection of two bovine cell lines. Furthermore, the LDL receptor was detected on the surface of CRIB cells. The functionality of the LDL receptor on CRIB cells was demonstrated by the internalization of fluorescently labeled LDL. In conclusion, at present no experimental evidence supports an involvement of the LDL receptor in BVDV invasion.     

Inactivation of bovine herpesvirus-1 and bovine viral diarrhea virus in association with preimplantation bovine embryos using photosensitive agents

Hematoporphyrin (HP), hematoporphyrin derivative (HPD), and thiopyronine (TP) are photosensitive agents (PSA) that have a germicidal effect when they are activated by light: helium neon laser (He Ne ) light (HP, HPD), white light (HP, HPD), and yellow-green light (TP). Experiments were conducted with appropriate controls to determine the effect of photosensitive agents a) for inactivating bovine herpesvirus-1 (BHV-1; titre 10(6) TCID(50) /ml) and bovine viral diarrhea virus (BVDV; titre 10(6) TCID(50) /ml); b) for disinfecting Day-7, zona pellucida-intact (ZP-I) bovine embryos that had been exposed to BHV-1 (titre 10(6) TCID(50) /ml) or BVDV (titre 10(6) TCID(50) /ml); and c) on the in vitro development of embryos. Exposure to HP, HPD and TP followed by light irradiation inactivated BHV-1 and BVDV. Embryos exposed to BHV-I were disinfected by HP or HPD (5 mug/ml) in combination with He Ne light, or by HP or HPD (10 mug/ml) in combination with white light. Embryos exposed to BVDV were disinfected by HPD (5 and 10 mug/ml) followed by He Ne or white light irradiation. Exposure of embryos to light alone or to light and HP or HPD had no detrimental effect on their in vitro development; however, exposure of embryos to TP (5 mug/ml) followed by irradiation caused embryonic degeneration. Exposure of embryos to 5 mug of HPD followed by He Ne light, or 10 mug/ml of HP or HPD, followed by white light, is simple methods of disinfecting them of BHV-I and BVDV.     

Washing and trypsin treatment of in vitro derived bovine embryos exposed to bovine viral diarrhea virus

Gametes, somatic cells and materials of animal origin in media are potential sources for introducing bovine viral diarrhea virus (BVDV) into systems for production of IVF bovine embryos. Further, the efficacy of washing and trypsin treatment for removal of BVDV from IVF embryos is questionable. Washing and trypsin treatments recommended by the International Embryo Transfer Society for in vivo-derived embryos were applied to in vitro-derived, virus-exposed, bovine embryos in this side-by-side comparison of treatments. Embryos for the study were produced in a virus-free system in which follicular oocytes were matured and fertilized in vitro and presumptive zygotes were co-cultured with bovine uterine tubal cells for 7 d. A total of 18 trials was performed, 9 using a noncytopathic BVDV and 9 using a cytopathic BVDV. In each trial, 4 equal groups of 10 or less, zona pellucida-intact embryos/ova were assembled, including 2 groups of morulae and blastocysts (M/B) and 2 groups of nonfertile or degenerated ova (NFD). Each group was prewashed and exposed to 10(4) to 10(6) TCID50/mL of either noncytopathic (SD-1) or cytopathic (NADL) BVDV for 2 h. Following in vitro viral exposure, one group of M/B and one group of NFD were washed. The other groups of M/B and NFD were trypsin-treated. Both treatments were consistent with IETS guidelines. After in vitro exposure to noncytopathic BVDV and washing, viral assays of 100% (9/9) and 78% (7/9) of the groups of M/B and NFD ova, respectively, were positive. After in vitro exposure to cytopathic BVDV and washing, viral assay of 33% (3/9) of the groups of both M/B and NFD ova were positive. After in vitro exposure to noncytopathic BVDV and trypsin treatment, viral assay of 44% (4/9) of groups of M/B and 67% (6/9) of groups of NFD ova were positive. Finally, after in vitro exposure to cytopathic BVDV and trypsin treatment, viral assay of 22% (2/9) of the groups of M/B and 44% (4/9) of the groups of NFD ova were positive. Contingency table analysis, in which data was stratified by embryo type and virus biotype, was used to compare results. While a difference existed between results of the 2 treatments of groups of M/B within the noncytopathic biotype (P = 0.01, Mantel Haenszel Chi-square), no difference was observed between comparison of treatment between all groups in both biotypes (P > 0.05).     

Cell-protective monoclonal antibodies to bovine enterovirus-3 and partial or no activity against other serotypes.

Preparation of monoclonal antibodies to bovine virus diarrhea virus (BVDV) yielded some hybridoma cells that secreted monoclonal antibodies against the Madin-Darby bovine kidney cells. The anti-cellular monoclonal antibodies reacted with other bovine cells (bovine turbinate and testicle) but not with cell lines derived from other animal species. Subclones derived from one hybridoma partially blocked the infectivity of BVDV, possibly through the binding of the monoclonal antibodies with an epitope close to the receptor site of BVDV and not by way of steric hindrance. Unexpectedly, these same subclones completely blocked the infectivity of bovine enterovirus-3 (BEV-3) strain 240A and partially blocked the infectivity of BEV-2 and BEV-3 (ATCC strain) but not that of other serotypes. Other subclones derived from two other hybridomas, although cell membrane specific, did not have a protective activity against BEV or BVDV.     

Intrauterine inoculation of seronegative heifers with bovine viral diarrhea virus concurrent with transfer of in vivo-derived bovine embryos

Bovine viral diarrhea virus (BVDV) has been shown to be associated with single transferable in vivo-derived bovine embryos despite washing and trypsin treatment. Hence, the primary objective was to evaluate the potential of BVDV to be transmitted via the intrauterine route at the time of embryo transfer. In vivo-derived bovine embryos (n = 10) were nonsurgically collected from a single Bos tarus donor cow negative for BVDV. After collection and washing, embryos were placed into transfer media containing BVDV (SD-1; Type 1a). Each of the 10 embryos was individually loaded into an 0.25-mL straw, which was then nonsurgically transferred into the uterus of 1 of the 10 seronegative recipients on Day 0. The total quantity of virus transferred into the uterus of each of the 10 Bos tarus recipients was 878 cell culture infective doses to the 50% end point (CCID₅₀)/mL. Additionally, control heifers received 1.5 × 10⁶ CCID₅₀ BVDV/.5 mL without an embryo (positive) or heat-inactivated BVDV (negative). The positive control heifer and all 10 recipients of virus-exposed embryos exhibited viremia by Day 6 and seroconverted by Day 15 after transfer. The negative control heifer did not exhibit a viremia or seroconvert. At 30 d after embryo transfer, 6 of 10 heifers in the treatment group were pregnant; however, 30 d later, only one was still pregnant. This fetus was nonviable and was positive for BVDV. In conclusion, the quantity of BVDV associated with bovine embryos after in vitro exposure can result in viremia and seroconversion of seronegative recipients after transfer into the uterus during diestrus.     

CD46 is a cellular receptor for bovine viral diarrhea virus

Various monoclonal antibodies (MAbs) that recognize cell surface proteins on bovine cells were previously shown to efficiently block infection with bovine viral diarrhea virus (BVDV) (C. Schelp, I. Greiser-Wilke, G. Wolf, M. Beer, V. Moennig, and B. Liess, Arch. Virol. 140:1997-2009, 1995). With one of these MAbs, a 50- to 58-kDa protein was purified from calf thymus by immunoaffinity chromatography. Microchemical analysis of two internal peptides revealed significant sequence homology to porcine and human CD46. The cDNA of bovine CD46 (CD46(bov)) was cloned and further characterized. Heterologously expressed CD46(bov) was detected by the MAb used for purification. A putative function of CD46(bov) as a BVDV receptor was studied with respect to virus binding and susceptibility of nonpermissive cells. While the expression of CD46(bov) correlated well with the binding of [(3)H]uridine-labeled BVDV, the susceptibility of cells nonpermissive for BVDV was not observed. However, the expression of CD46(bov) resulted in a significant increase in the susceptibility of porcine cells to BVDV. These results provide strong evidence that CD46(bov) serves as a cellular receptor for BVDV.     

Alteration in ultrastructural morphology of bovine embryos following subzonal microinjection of bovine viral diarrhea virus (BVDV)

The aim of the present study was to evaluate the development and ultrastructure of preimplantation bovine embryos that were exposed to bovine viral diarrhea virus (BVDV) in vitro.The embryos were recovered from superovulated and fertilized Holstein-Friesian donor cows on day 6 of the estrous cycle. Compact morulae were microinjected with 20 pl of BVDV suspension (10(5.16) TCID(50)/ml viral stock diluted 1:4) under the zona pellucida (ZP), then washed in SOF medium and cultured for 24-48 h. Embryos were evaluated for developmental stages and then processed immunocytochemically for the presence of viral particles, using fluorescent anti-BVDV-FITC conjugate. Ultrastructure of cellular organelles was analysed by transmission electron microscopy (TEM).After microinjection of BVDV under the ZP, significantly more (p<0.001) embryos (83.33%) were arrested at the morula stage compared with the intact control (30.33%). Immunocytochemical analysis localized the BVDV-FITC signal inside the microinjected embryos. TEM revealed: (i) the presence of virus-like particles in the dilated endoplasmic reticulum and in cytoplasmic vacuoles of the trophoblast and embryoblast cells; (ii) the loss of microarchitecture: and (iii) abnormal disintegrated nuclei, which lacked reticular structure and the heterochromatin area. In all, the embryo nuclear structure was altered and the microarchitecture of the nucleolus had disappeared when compared with the nuclei from control embryos. Dilatation of the intercellular space and the loss of the intercellular gap junctions were often observed in bovine BVDV-exposed embryos.These findings provide evidence for the adverse effect of BVDV virus on the development of bovine embryos, which is related to irreversible changes in the ultrastructure of cell organelles.     

Recovery of cytopathogenic and noncytopathogenic bovine viral diarrhea viruses from cDNA constructs.

After cDNA cloning of the genome of bovine viral diarrhea virus (BVDV) isolate CP7, a full-length cDNA clone was constructed. RNA transcribed in vitro from this construct was shown to direct the generation of infectious BVDV upon transfection into bovine cells. To confirm the de novo generation of infectious BVDV from cloned cDNA a genetically tagged virus was constructed. In comparison with parental BVDV, the recombinant virus was slightly retarded in growth. The NS2 coding region of the CP7 genome contains a duplication of 27 nucleotides which is not present in the genome of its noncytopathogenic counterpart, NCP7. Exchange of a small fragment harboring this insertion against the corresponding part of the NCP7 sequence led to recovery of noncytopathogenic BVDV. Alteration of the construct by introduction of a fragment derived from a cytopathogenic BVDV defective interfering particle resulted in a chimeric defective interfering particle which exhibits a cytopathogenic phenotype. These findings confirm the hypothesis that the recombination-induced alterations in the genomes of cytopathogenic BVDV are responsible for the induction of cell lysis.     

Viremia and virus shedding in elk infected with type 1 and virulent type 2 bovine viral diarrhea virus

In order to determine whether elk (Cervus elaphus) could be infected with and shed bovine viral diarrhea virus (BVDV) and to determine whether BVDV could cause disease in elk, two groups of five yearling elk each and two control cattle were experimentally inoculated intranasally with type 1 Singer strain or a virulent type 2 isolate of BVDV, strain 24515. Virulence of the type 2 isolate was confirmed by inoculation of a control bovine cow which developed diarrhea, dehydration, severe thrombocytopenia, hemorrhages, and enteritis with intestinal necrosis. None of the elk inoculated with type 1 or type 2 BVDV developed clinical signs of illness. However, all elk became infected as demonstrated by viremia, nasal shedding, and/or seroconversion. One uninoculated, in-contact elk contracted type 1 BVDV and seroconverted. Thus, although BVDV does not appear capable of producing disease in nonpregnant elk, the species is susceptible to infection and can shed and transmit BVDV.     

Detection of bovine viral diarrhea virus (BVDV) in single or small groups of preimplantation bovine embryos

The objectives of this study were to develop techniques to detect BVDV associated with single or small groups of bovine embryos contained in small aliquots of medium using either virus isolation (VI) or real time quantitative polymerase chain reaction (RT-QPCR) assays. In vivo-derived and in vitro-produced bovine embryos at 7 d post-fertilization were exposed to SD-1, a high affinity strain of BVDV, for 2 h and then processed according to the International Embryo Transfer Society (IETS) guidelines prior to testing. Groups of five or two in vivo-derived embryos, and single in vivo-derived embryos, were VI positive for BVDV 100, 50, and 33% of the time, and were RT-QPCR positive 100, 75, and 42% of the time, respectively. The virus was detected by the VI technique in all of the groups of five or two in vitro-produced embryos and in all of the single in vitro-produced embryos, and it was detected in 100, 80, and 50%, using RT-QPCR. Techniques for RT-QPCR were sufficiently sensitive to detect 10 copies of viral RNA in a sample and to detect BVDV associated with single embryos. Application of this new technology, RT-QPCR, will facilitate additional studies to further assess the risk of transmission of BVDV through embryo transfer.     

我国牛病毒性腹泻流行现状与防控策略

我国牛病毒性腹泻病(Bovine viral diarrhea,BVD)的流行比较复杂,其病原BVDV (BVDV-1和BVDV-2)不仅仅局限于已知易感动物牛群感染,其他动物种群中感染BVDV-1和BVDV-2的现象也值得注意,如猪群中BVDV感染很大程度上混淆了猪瘟等病原的监测,从而加剧病程发展。牛病毒性腹泻病毒(Bovine viral diarrhea virus,BVDV)可致持续感染(Persistent infection,PI),这一特性导致该病的净化面临巨大困难,对整个养殖场的健康发展形成了严峻威胁。BVDV抗原变异速率非常快,目前BVDV-1已有22个亚型,BVDV-2有4个亚型,鉴于病原在自然界的适应和演进特性,对该病的防控措施迟后其病原的变异速度。因此,定期摸清BVDV-1和BVDV-2在我国的流行现状是实施疫病净化的第一步和关键步骤,进一步借鉴国外BVD净化成功经验,综合考虑我国国情,采取适宜的防控策略,逐步净化该病原感染,有助于促进国内养殖业的健康发展。     

A sensitive and efficient detection method for bovine viral diarrhea virus (BVDV) in single preimplantation bovine embryos

The objective was to develop a method to accurately and efficiently detect minute amounts of bovine viral diarrhea virus (BVDV) associated with a single embryo. There are two major challenges for BVDV detection in a single embryo: the test sensitivity and the efficiency of viral molecule recovery. These become even more critical when attempts are made to detect BVDV infections that occurred naturally, not through artificial exposure of the embryos to high affinity BVDV strains. We have developed a one-step sample preparation method that has increased the viral molecule recovery rate compared to the standard RNA isolation procedure by 7-100-fold. Instead of using the traditional virus exposure approach, we generated BVDV positive embryos via somatic cell nuclear transfer (SCNT) technology using BVDV positive donor cells. By combining the highly efficient sample preparation procedure with a sensitive one-step, real-time PCR system, we have developed a sensitive test that allows detection of as low as two copies of BVDV in a single embryo. This method will allow systematic risk assessment for BVDV transmission during in vitro embryo production via IVF or SCNT procedures.     

Acid-resistant bovine pestivirus requires activation for pH-triggered fusion during entry

The route of internalization of the pestivirus bovine viral diarrhea virus (BVDV) was studied by using different chemical and biophysical inhibitors of endocytosis. Expression of the dominant-negative mutant Dyn(K44A) of the GTPase dynamin in MDBK cells, as well as the treatment of the cells with chlorpromazine and beta-methyl-cyclodextrin inhibited BVDV entry. BVDV infection was also abolished by potassium (K+) depletion, hyperosmolarity, and different inhibitors of endosomal acidification. We conclude that BVDV likely enters the cell by clathrin-dependent endocytosis and that acidification initiates fusion with the endosomal membrane. Further studies revealed that BVDV was unable to undergo "fusion from without" at low pH. The finding that low pH is not sufficient to force adsorbed BVDV into fusion with the plasma membrane is compatible with the remarkable resistance of pestiviruses to inactivation by low pH. The importance of the abundant intra- and intermolecular disulfide bonds in BVDV glycoproteins for virus stability was studied by the use of reducing agents. The combination of dithiothreitol and acidic pH led to partial inactivation of BVDV and allowed fusion from without at low efficiency. Evidence is provided here that acid-resistant BVDV is destabilized during endocytosis to become fusogenic at an endosomal acidic pH. We suggest that destabilization of the virion occurs by breakage of disulfide bonds in the glycoproteins by an unknown mechanism.     

Laboratory diagnosis of bovine viral diarrhea virus

The control and eventual eradication of bovine viral diarrhea virus (BVDV) have been defined as objectives to reduce the economic losses due to the presence of this virus in the cattle population. These goals could not be envisioned without the significant achievements in the diagnostic procedures employed to detect the infection in its various manifestations. The tests that are currently available are fully capable of supporting the ACVIM consensus statement for the control and eradication of BVDV. In point of fact diagnostic testing is the essential component of any control program. What is now currently lacking is full implementation of the ACVIM recommendations.     

Noncytopathic bovine viral diarrhea virus in a system for in vitro production of bovine embryos

Techniques for in vitro production of bovine embryos have evolved to the extent that applications for the commercial production of calves have been proposed. However, little is known about the epidemiological implications of the procedures. One concern is the introduction of noncytopathic bovine viral diarrhea virus (BVDV). In this study, follicular oocytes (n=247) collected from 10 cows were matured and fertilized in vitro and presumptive zygotes were cultured for 7 d. Primary cultures of bovine oviductal epithelial cells for use during in vitro fertilization and culture were divided into 2 groups. Treated oviductal cells were infected with BVDV while control cells were not exposed to the virus. Two approximately equal groups of mature oocytes from each cow were inseminated, and the presumptive zygotes were cultured with infected or noninfected oviductal cells. After 7 d in culture, zona pellucida-intact morulae/blastocysts and degenerated ova were washed, sonicated and assayed for the presence of virus. The rates of cleavage and development were also compared by Chi-square analysis. After washing, virus was not isolated from morulae and blastocysts but was isolated from some groups of degenerated ova. Infections of oviductal cells were inapparent and did not significantly (P>0.05) affect rates of cleavage or development.