The persistence of bovine viral diarrhea virus.

Bovine viral diarrhoea virus (BVDV) has a unique capacity to cause persistent infections of foetuses exposed within the first 150 days of gestation. Preventing foetal BVDV infection will aid in improved control. This unique ability gives BVDV a selective advantage allowing continual mutation and antigenic variation within cattle populations. Therefore, BVDV has become widespread and causes economic losses due to respiratory, reproductive and enteric disease. Vaccination (modified-live or killed) can provide some protection from acute disease and the development of persistently infected foetuses. However, vaccination programmes alone cannot control or eliminate BVDV. In naturally exposed and vaccinated herds, BVDV infections are not self-limiting and may persistent over time. This underscores the ability of the BVDV genome to remain fluid and adapt under selective pressures. Factors influencing persistence of BVDV infections in cattle populations include: non-lytic infections; evasion of host immune responses; foetal infections; acute infections; management practices; contaminated biologics; secondary hosts; defective replicated intermediates; antigenic variation; and replication in privileged anatomical sites.     

An Experimental Study of a Concurrent Primary Infection with Bovine Respiratory Syncytial Virus (BRSV) and Bovine Viral Diarrhoea Virus (BVDV) in Calves

Experimental infections with bovine respiratory syncytial virus (BRSV) and bovine viral diarrhoea virus (BVDV) were performed to study the effect of concurrent BRSV and BVDV infections. Twelve seronegative calves, in 3 groups, were inoculated on a single occasion with pure BRSV (group A), BRSV and noncytopathogenic BVDV (group B) or mock infected (group C). Mild respiratory symptoms were recorded 4 to 5 days post inoculation (dpi) in group A and group B calves. One calf in group A was severely affected and required medical treatment. In group B, fever (40.7-41.4 °C) was prominent 7 to 8 dpi. Only calves in group B were BVDV positive in purified lymphocytes at 2 to 14 dpi and showed increased serum interferon levels, with a peak at 4 dpi, indicating BVDV to be responsible for inducing the rise. BRSV was detected in lung lavage fluids up to 7 dpi for group A calves, compared to 11 dpi for group B and calves in this group also seroconverted later displaying lower BRSV titers. The time lag before an antibody response and the titers recorded in group B, indicated that the duration of BVDV infection in lymphocytes negatively influenced the capacity to mount a BRSV antibody response. kw|Keywords|k]cattle; k]respiratory disease; k]interferon; k]PCR     

Bovine maternal,fetal and neonatal responses to bovine viral diarrhea virus infections

Due to the affinity of BVDV for the fetus and for cells of lymphatic organs of infected cattle, reproductive failure or immunosuppression, respectively, are likely consequences of BVDV infections of susceptible cattle. Infection of susceptible pregnant cattle with noncytopathic (ncp) BVDV results in transplacental infection with induction of maternal and fetal innate and adaptive immune responses. Differences in maternal innate and adaptive immune responses are evident in late gestation between cows carrying fetuses persistently-infected (PI) with BVDV and cows with fetuses transiently-infected with BVDV. Fetal innate and adaptive immune responses to ncp BVDV infection are defined by fetal age and developmental stage of the fetal immune system. Since a functional fetal adaptive immune response does not occur in the early fetus, immunotolerance to ncp BVDV is established, virus replicates unrestricted in fetal tissues and calves are born immunotolerant and PI with the virus. In the last trimester of gestation, the fetal immune system is adequately developed to respond in an efficacious manner, most commonly resulting in the birth of a clinically normal calf with pre-colostral antibodies. Immunosuppression due to postnatal acute ncp BVDV infections of susceptible calves may contribute to the occurrence and severity of multi-factorial respiratory tract and enteric diseases.     

Seroepidemiology of bovine viral diarrhoea virus (BVDV) in the Adamawa Region of Cameroon and use of the SPOT test to identify herds with PI calves

Bovine viral diarrhoea, caused by the bovine viral diarrhoea virus (BVDV) in the Pestivirus genus of the Flaviviridae, is one of the most important diseases of cattle world wide causing poor reproductive performance in adult cattle and mucosal disease in calves. In addition it causes immunosuppression and increased susceptibility to other infections, the impact of which is uncertain, particularly in sub-Saharan Africa where animals are exposed to a much wider range and higher intensity of infections compared to Europe. There are no previous estimates of the seroprevalence of BVDV in cattle in Cameroon. This paper describes the serological screening for antibodies to BVDV and antigen of BVDV in a cattle population in the Adamawa Region of Cameroon in 2000. The estimates of herd-level and within herd seroprevalences adjusted for test imperfections were 92% and 30% respectively and 16.5% of herds were classed as having a persistently infected calf (PI) in the herd within the last year based on the "spot" test approach. There was evidence of clustering of herds with PI calves across the north and west of the Region which corresponds with the higher cattle density areas and of self-clearance of infection from herds. A multivariable model was developed for the risk of having a PI calf in the herd; proximity to antelope, owning a goat, mixing with > 10 other herds at grazing and the catchment area of the veterinary centre the herd was registered at were all significant risk factors. Very little is known about BVDV in sub-Saharan Africa and these high seroprevalences suggest that there is a large problem which may be having both direct impacts on fertility and neonate mortality and morbidity and also indirect effects through immunosuppression and susceptibility to other infections. Understanding and accounting for BVDV should be an important component of epidemiological studies of other diseases in sub-Saharan Africa.     

Detection and Characterization of Pestivirus Contaminations in Human Live Viral Vaccines

In view of the use of potentially contaminated foetal calf serum (FCS) in cell cultures pestiviruses may be present in live viral vaccines. Thirty-six lots of human live viral vaccines produced by three manufacturers were tested for the presence of pestiviruses. Bovine viral diarrhoea virus (BVDV) RNA was detected in 33% of the vaccine lots. All positive results were caused by the mumps component of a single manufacturer. Partial sequences of the 5' untranslated region of BVD viral RNA were determined. The sequences were closely related to that of the NADL strain of BVDV. The amount of BVDV RNA in the vaccines was determined by real-time RT-PCR using the LightCycler. Between 3.3*10(2) and 6.2*10(5) RNA copies per dose were found to be present in the vaccine samples.Additionally, culture tests were done with FCS and human diploid cells used in the vaccine production of the manufacturer whose vaccines were positive by PCR. All attempts to detect virus antigen in MRC-5 human diploid cells or to infect these cells with BVDV failed. This suggests that BVDV RNA detected in human live viral vaccines represents passive carry over of BVDV from contaminated FCS rather than active virus replication in human diploid cells. Our results indicate that contamination with BVDV of FCS used in vaccine production does not appear to be of immediate concern to human health. Furthermore, our results indicate that gamma-irradiation of FCS destroys BVDV particles and is also effective in preventing the presence of BVDV RNA in the vaccines.     

BVDV and innate immunity.

Infection with bovine viral diarrhea virus (BVDV) is prevalent in the cattle population worldwide. The virus exists in two biotypes, cytopathic and non-cytopathic, depending on the effect of the viruses on cultured cells. BVDV may cause transient and persistent infections which differ fundamentally in the host's antiviral immune response. Transient infection may be due to both cytopathic and non-cytopathic biotypes of BVDV and leads to a specific immune response. In contrast, only non-cytopathic BVD viruses can establish persistent infection as a result of infection of the embryo early in its development. Persistent infection is characterized by immunotolerance specific for the infecting viral strain. In this paper we discuss the role of innate immune responses in the two types of infection. In general, both transient and persistent infections are associated with an increased frequency of secondary infections. Associated with the increased risk of such infections are, among others, impaired bacteria killing and decreased chemotaxis. Interestingly, non-cytopathic BVDV fails to induce interferon type I in cultured bovine macrophages whereas cytopathic biotypes readily trigger this response. Cells infected with non-cytopathic BVDV are also resistant to induction of interferon by double stranded RNA, a potent interferon inducer signalling the presence of viral replication in the cell. Thus, non-cytopathic BVDV may dispose of a mechanism suppressing a key element of the antiviral defence of the innate immune system. Since interferon is also important in the activation of the adaptive immune response, suppression of this signal may be essential for the establishment of persistent infection and immunotolerance.     

Immunology of chronic BVDV infections

Bovine viral diarrhea virus can maintain prolonged infections within immunoprivileged sites after an otherwise transient infection of a cow, calf, or bull. Various sites provide unique niches for viral replication which are not susceptible to the complete surveillance commonly provided by the bovine immune system. Evidence indicates that pestiviral infections may be significantly prolonged within ovarian tissue, testicular tissue, central nervous system tissue, and circulating white blood cells. Within avascular portions of the ovarian follicle, granulosa cells and oocytes may maintain BVDV infections which cannot be attacked by cell-mediated immunity. When infections occur within seminiferous tubules in testicular tissue, similar protection from the immune system is provided for BVDV by the blood-testes barrier. Likewise, the blood-brain barrier has been hypothesized to provide protection for BVDV in a case involving neuropathology associated with immunohistochemical detection of BVDV. Furthermore, infections of circulating white blood cells may perturb their stimulation of an adaptive immune response and facilitate chronic infection of these cells. Thus, BVDV has demonstrated an ability to maintain prolonged viral infections in immunoprivileged sites within its natural host. The role of chronic infections in maintaining and disseminating BVDV within the cattle population and heterologous host species remains to be fully understood.     

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。     

Bovine viral diarrhea infections in new world camelids—A review

Bovine virus diarrhea virus (BVDV) has recently been identified as an important infectious disease of new world camelids (NWC) particularly alpacas. Both sub-genotypes 1a, 1b and genotype 2 have been isolated. However, non-cytopathic BVDV 1b is reported to be primarily implicated in cases of BVDV in NWC's. Although suspected a BVDV strain unique to camelids have not been isolated. The most important source of BVDV is the immuno-tolerant persistently infected cria. Natural transient infection of BVDV in NWCs is reported to go almost undetected except for vague signs of illness, including lethargy and anorexia. Diarrhea does not appear to be a constant finding. Embryonal/fetal disease in NWC's includes early pregnancy loss, abortion and premature birth or the birth of persistently infected crias. Persistently infected disease can occur in both acute and chronic forms. In NWCs the chronic form of the condition is most commonly reported. Signs include chronic ill-thrift, poor weight gain or being underweight, intermittent illness, chronic diarrhea, joint swelling and episodes of nasal discharge and pneumonia despite antibiotic treatment. The mortality rate in NWCs appears to be close to 100%. Seroprevalence of BVDV in NWCs ranged from 2.05% to 11.11% however the possibility that the correct (homologous) BVDV strain is not being used in serological assays need to be considered. The importance of cattle as a source of BVDV for camelids is unclear although there is consensus of a spill-over from cattle to NWC's. Assays available for BVDV in cattle appear to work for camelids. An antigen ELISA which is the usual method for detecting BVD in cattle has not been validated in NWC's.     

Evaluation of risks of viral transmission to recipients of bovine embryos arising from fertilisation with virus-infected semen

This scientific review was prompted by recent legislation to curtail the use of semen from potentially virus-infected bulls to produce embryos for import into the European Union. From studies in laboratory animals, humans and horses, it is apparent that viruses may sometimes attach to, or be integrated into, spermatozoa, although in domestic livestock, including cattle, this seems to be a rare phenomenon, and carriage of virus through the zona pellucida into the oocyte by fertilising sperm has never been described in these species. Four specific viruses; enzootic bovine leukosis (EBLV), bovine herpesvirus-1 (BoHV-1), bovine viral diarrhoea virus (BVDV) and bluetongue virus (BTV), all of which tend to cause subclinical infections in cattle, but which can occur in bovine semen, are examined with regard to the risks that use of infected semen might lead to production of infected embryos. With regard to in vivo-derived embryos, when internationally approved embryo processing protocols are used, the risks from EBLV- and BTV-infected semen are negligible, and the same is almost certainly true for semen infected with BoHV-1 if the embryos are also treated with trypsin. For BVDV, there is insufficient data on how the virus is carried in semen and how different BVDV strains can interact with sperm, oocytes and embryos. There is a potential, at least, that in vivo-derived embryos resulting from infected semen might carry BVDV, although field studies so far suggest that this is very unlikely. With regard to in vitro-produced embryos, use of semen infected with any of the four viruses, with the probable exception of EBLV, will often lead to contaminated embryos, and virus removal from these embryos is difficult even when the internationally approved embryo processing protocols are used. However, it has never been demonstrated that such embryos have resulted in transmission of infection to recipients or offspring.     

Bovine viral diarrhoea virus antigen in foetal calf serum batches and consequences of such contamination for vaccine production.

A protocol to test foetal calf serum (FCS) for contamination with bovine viral diarrhoea virus (BVDV) is described. Following this protocol, which combines cell culture methods and detection of pestivirus RNA, seven batches of FCS were tested. Infectious BVDV was detected in four of those batches. One of the remaining batches contained a relatively high number of non-infectious BVDV particles. A sample of this batch was formulated with aluminium hydroxide and aluminium phosphate as adjuvant into an experimental vaccine preparation. This product was injected twice into BVDV seronegative cattle with a 4 week interval. Blood samples taken 4 weeks after the second application were negative for BVDV specific antibodies. Our data stress that detection of BVDV RNA is not sufficient for a complete risk assessment on FCS. Discrimination between infectious and non-infectious BVDV is essential. This can only be achieved by cell culture methods.     

Immune response to vaccination with DNA encoding the bovine viral diarrhea virus major glycoprotein gp53 (E2)

Bovine viral diarrhea virus (BVDV) is a worldwide pathogen in cattle which has not been controlled by classical vaccination. The region encoding the BVDV major glycoprotein gp53 (E2) known to possess virus-neutralizing activity was cloned into a mammalian expression vector under the human cytomegalovirus (CMV) intermediate early promoter. Intramuscular and intradermal administration of the recombinant plasmid DNA into BALB/c mice induced BVDV gp53-specific antibody responses to both biotypes (cytopathic and noncytopathic) of BVDV genotype 1, and to cytopathic BVDV genotype 2. BVDV-neutralizing antibodies were generated against BVDV genotype 1 strains and they also persisted 6 months after the last injection.     

Diva vaccines that reduce virus transmission.

This brief review deals with the effect of diva (Differentiating Infected from VAccinated individuals) vaccines (also termed marker vaccines) on transmission of herpesviruses and pestiviruses in swine and cattle. Pseudorabies and bovine herpesvirus 1 diva vaccines have been demonstrated to reduce transmission of wild-type virus in populations of pigs and cattle in the laboratory as well as in the field. A subunit diva vaccine based on the immunodominant E2 protein of classical swine fever virus that is expressed in the baculovirus system may reduce transmission of wild-type virus among pigs and also transmission from mother to foetuses. A similar diva vaccine against bovine virus diarrhoea infections protected sheep against transplacental transmission of antigenically homologous wild-type virus. Diva vaccines along with their companion diagnostic tests can play a role in control of infections, ultimately leading to eradication of viruses.     

Molecular and in vitro Characterization of Field Isolates of Bovine Herpesvirus-1

Bovine Herpesvirus-1 (BoHV-1) is distributed worldwide and is a major pathogen in cattle, being the causal agent of a variety of clinical syndromes. The aim of this study was to isolate and to characterize (molecular and biological characterization) BoHV-1 from 29 immunosuppressed animals. It was possible to obtain 18 isolates, each from a different animal, such as from the respiratory and reproductive tracts. In some cases the cytopathic effect was visible 12 hours post-inoculation, and became characteristic after 36-48 hours. Biological characteristics were evaluated and compared with Iowa and Colorado-1 reference strains, and differences were found in plaque size, virus titer measured by TCID50 and PFU/mL, and one step virus curves. These results showed that some isolates had a highly virulent-like behavior in vitro, compared to the reference strains, with shorter eclipse periods, faster release of virus into the supernatants, and higher burst size and viral titer. There were no differences in glycoprotein expression of BoHV-1 isolates, measured by Western blot on monolayers. Moreover, using restriction endonucleases analysis, most of the viruses were confirmed as BoHV-1.1 and just one of them was confirmed as BoHV-1.2a subtype. These findings suggest that some wild-type BoHV-1 isolates could be useful as seeds to develop new monovalent vaccines.     

Preparation of chicken IgY against recombinant E2 protein of bovine viral diarrhea virus (BVDV) and development of ELISA and ICA for BVDV detection

Bovine viral diarrhea virus (BVDV) infects cattle and may lead to persistent infection (PI). The PI animals harbor BVDV throughout their life and become immune tolerant against BVDV. Thus, diagnosis of this virus in herd is highly important. Recombinant E2 protein expression (using pET-32a in Escherichia coli) was confirmed by SDS-PAGE and Western blotting; then purified by Ni⁺ affinity chromatography. Chickens were immunized with BVDV-E2 protein, and IgY antibodies were extracted from egg yolk by PEG-6000. The peak titer of anti-BVDV-E2-IgY was 1:128,000 after the fifth immunization. IgY-based enzyme-linked immuno sorbent assay (ELISA) and immunochromatographic assay (ICA) were further developed. Coincidence of ELISA and ICA test with RT-PCR was 95.45 and 90.91%, respectively. The anti-BVDV-E2 IgY could be used in routine screening of BVDV infection. Besides, it can also be applicable while licensing and/or using live vaccines; screening of imported products containing bovine serum and strong surveillance of BVDV outbreaks.     

Characterization of Immune Responses Induced by Immunization with the HA DNA Vaccines of Two Antigenically Distinctive H5N1 HPAIV Isolates

The evolution of the H5N1 highly pathogenic avian influenza virus (HPAIV) has resulted in high sequence variations and diverse antigenic properties in circulating viral isolates. We investigated immune responses induced by HA DNA vaccines of two contemporary H5N1 HPAIV isolates, A/bar-headed goose/Qinghai/3/2005 (QH) and A/chicken/Shanxi/2/2006 (SX) respectively, against the homologous as well as the heterologous virus isolate for comparison. Characterization of antibody responses induced by immunization with QH-HA and SX-HA DNA vaccines showed that the two isolates are antigenically distinctive. Interestingly, after immunization with the QH-HA DNA vaccine, subsequent boosting with the SX-HA DNA vaccine significantly augmented antibody responses against the QH isolate but only induced low levels of antibody responses against the SX isolate. Conversely, after immunization with the SX-HA DNA vaccine, subsequent boosting with the QH-HA DNA vaccine significantly augmented antibody responses against the SX isolate but only induced low levels of antibody responses against the QH isolate. In contrast to the antibody responses, cross-reactive T cell responses are readily detected between these two isolates at similar levels. These results indicate the existence of original antigenic sin (OAS) between concurrently circulating H5N1 HPAIV strains, which may need to be taken into consideration in vaccine development against the potential H5N1 HPAIV pandemic.