Evaluation of a commercial Erns-capture ELISA for detection of BVDV in routine diagnostic cattle serum samples

The Epidemiology of Bovine Viral Diarrhea Virus in Low- and Middle-Income Countries: A Systematic Review and Meta-Analysis

Introduction

Bovine viral diarrhea virus (BVDV) causes reproductive inefficiencies and negatively impacts the economy of low- and middle-income countries (LMICs). It is characterized by a combination of syndromes that result in poor production performance and calf morbidity and mortality. BVDV control is possible by introduction of biosecurity measures, test-and-cull, and vaccination programs as accomplished in high-income countries. Knowledge of BVDV epidemiology is limited in many LMICs, which hinders implementation of effective control programs. We carried out a systematic review and meta-analysis to estimate the burden of BVDV, identify risk factors related to its occurrence, and health and economic impacts on production systems.

Materials and Methods

Relevant BVD articles were collated from library databases; 690 abstracts and full texts were found in an initial search followed by filtering of 59 manuscripts. We accounted for quality and risk of bias in the meta-analysis. Prevalence, exposure, and current infection at regional, production, and farming system levels were estimated using logistic random-effects meta-regression models. Finally, we calculated the proportion of studies that addressed risk factors and health and economic impacts across different production systems to inform future preventative strategies in LMICs.

Results

Seroprevalence was high and varied between regions. Mean weighted prevalence was 39.5% (95% CI 25-56.1), 45.2% (95% CI 35.9-54.8), 49.9% (95% CI 25.5-74.3), and 21.6% (95% CI 0.5-56) for sub-Saharan Africa, South America, Middle East, and Asia, respectively. Seroprevalence varied across farming systems, with smallholder farming showing the highest values. Herdsize was the most frequently reported risk factor, and the percentage of articles that reported herdsize as a risk factor were 20.6%, 33.3%, and 38.4% for dairy, beef and mixed systems respectively. Abortion (13.7% of articles) was the main reported health impact in dairy systems. Some articles reported milk drop (4.6% of articles), but no article investigated the economic cost of BVDV in farming systems.

Conclusion

Animal-level seroprevalence varied across all regions. Most of the studies focused on BVDV seroprevalence. There were some articles that investigated risk factors and health impacts, and there were even less that investigated economic impacts. Future studies should focus on identifying risk factors and quantifying health and economic impacts across systems. Understanding these aspects is crucial to develop management strategies to apply across diverse production systems in LMICs.

Immunization with recombinant Erns-LTB fusion protein elicits protective immune responses against bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV), a major infectious pathogen and is associated with major economic losses and significant impact on animal welfare worldwide. Here, recombinant E^rns-LTB protein vaccine containing MF59 adjuvant was prepared and assessed using a mouse model. The recombinant plasmid (pET32a-E^rns-LTB) was constructed and transformed into BL21 (DE3) cells to produce E^rns-LTB protein. The E^rns-LTB protein was formulated with MF59 adjuvant, when delivered intraperitoneally in mice, exhibited higher immunogenic and induced superior levels of anti-BVDV IgG compared with the MF59 adjuvanted E^rns protein. Importantly, after challenged with different BVDV BJ175170 and BJ1305 isolate strains, mice inoculated with E^rns-LTB protein displayed alleviated pathological damage and decreased plasma virus shedding compared with mice inoculated with E^rns protein. The enhanced protection from E^rns-LTB protein is mediated by T cell immunity and primarily based on CD4⁺ T helper (Th) and CD8⁺ cytotoxic T lymphocyte (CTL), these results suggest that E^rns-LTB protein has potential to protect against a broad range of BVDV strains thereby providing a novel direction for developing broadly protective vaccines.

Replicon Particle Expressing the E2 Glycoprotein of Bovine Viral Diarrhea Virus Immunization and Evaluation of Antibody Response

The objective of this study was to develop a new antigen delivery system using an alphavirus replicon particle (RP) to induce humoral antibody responses against bovine viral diarrhea virus (BVDV) recombinant antigen produced from envelope glycoprotein E2. An alphavirus RP expressing the E2 glycoprotein of BVDV was used for immunization of pigs. A fluorescent microsphere immunoassay (FMIA) has been applied to detect BVDV E2 antigen-specific antibody isotype in pig immunized with alphavirus RP. Full-length BVDV E2 (aa 1-375) was cleaved into several pieces, eight E2 DNA fragments, including full-length DNA, were cloned into expression vector pHUE, and the recombinant proteins expressed in BL-21 (DE3) Escherichia coli. After successful conjugation of purified proteins with microsphere beads, a multiplex FMIA platform was constructed, and BVDV E2 alphavirus-based RP-immunized animal serum samples were tested in the presence of bead-bound antigen targets. The results were represented as mean fluorescence intensity (MFI); the MFI values were converted to sample value/positive value (S/P) ratios. BVDV E2 (aa 1-183) showed the highest MFI values of eight recombinant E2 fragments when the specific activity of each fragment was tested. In immunized animals, data for BVDV E2-specific IgA, IgG, and IgM in serum and only IgG and IgA in oral fluids were recorded. The MFI values for the positive serum sample showed a 100-fold increase compared with the negative serum sample. Antibody isotype to BVDV E2 antigens showed that IgG > IgM > IgA in serum, whereas IgG > IgA > IgM in oral fluids. The data presented in this study suggested that boosting with the same doses of alphavirus RP in 3-week intervals may potentially enhance antibody response. The experimental results demonstrate that alphavirus RP-expressing BVDV E2 antigen induces antibody response in pig.

Roles of bta-miR-29b promoter regions DNA methylation in regulating miR-29b expression and bovine viral diarrhea virus NADL replication in MDBK cells

MicroRNAs (miRNAs) are an important class of small, non-coding RNAs that control target genes expression by degradation of target mRNAs or by inhibiting protein translation in many biological processes and cellular pathways. In a previous study, we found that miR-29b interfered with bovine viral diarrhea virus (BVDV) replication. However, the mechanisms of regulation of miR-29b expression are not well known. DNA methylation is an important epigenetic mechanism for silencing gene transcription, and plays an important role in promoter choice, protein expression, and regulation of miRNAs expression. In this study, we focused on the roles of DNA methylation of miR-29b promoter in regulating miR-29b expression and investigated the effects of DNA (cytosine-5) methyltransferase 1 (DNMT1) knockdown on miR-29b expression and BVDV (strain NADL) replication. Our results showed that methylation levels of miR-29b promoter were significantly decreased in BVDV NADL-infected MDBK cells. Furthermore, DNMT1 silencing significantly decreased the methylation levels of miR-29b promoter, up-regulated miR-29b expression and inhibited BVDV NADL replication, which supports the important roles of DNA methylation in regulating miRNA expression and further proves an evidence for our previous views.

Evaluation of envelope glycoprotein E(rns) of an atypical bovine pestivirus as antigen in a microsphere immunoassay for the detection of antibodies against bovine viral diarrhea virus 1 and atypical bovine pestivirus

Atypical bovine pestiviruses are related antigenically and phylogenetically to bovine viral diarrhea viruses (BVDV-1 and BVDV-2), and may cause the same clinical manifestations in animals. Glycoprotein E(rns) of an atypical bovine pestivirus Th/04_KhonKaen was produced in a baculovirus expression system and was purified by affinity chromatography. The recombinant E(rns) protein was used as an antigen in a microsphere immunoassay for the detection of antibodies against BVDV-1 and atypical bovine pestivirus. The diagnostic performance of the new method was evaluated by testing a total of 596 serum samples, and the assay was compared with enzyme-linked immunosorbent assay (ELISA). Based on the negative/positive cut-off median fluorescence intensity (MFI) value of 2800, the microsphere immunoassay had a sensitivity of 100% and specificity of 100% compared to ELISA. The immunoassay was able to detect antibodies against both BVDV-1 and the atypical pestivirus. This novel microsphere immunoassay has the potential to be multiplexed for simultaneous detection of antibodies against different bovine pathogens in a high-throughput and economical way.

The diagnosis and prevalence of persistent infection with bovine viral diarrhoea virus in South African feedlot cattle

Bovine viral diarrhoea virus (BVDV) infection is an important viral infection affecting the cattle industry today. The prevalence of this infection in South African feedlots is unknown. Ear notch biopsies were collected from chronic poor doers and animals that appeared unthrifty upon entering feedlots, as well as animals entering the hospital pen with respiratory disease for the first time. A total of 1690 samples were collected: 1074 from the former category and 616 from the latter. A routine immunohistochemistry staining protocol showed that 49 animals tested positive, of which 43 (4%) came from the feedlot entry group and six (1%) from the hospitalised group. The prevalence of persistently infected cattle from this selected, nonrandom sample entering six large South African feedlots was found to be 2.9%, which is higher than the international rule of thumb that 0.5% of all cattle entering feedlots are persistently infected. There was no clear correlation between persistent infection and respiratory disease. Serum samples were also collected when possible and 10 positive cases were found. Results from enzyme-linked immunosorbent assays for antigen and antibody performed on these sera correlated well with those from the immunohistochemistry staining method in six cases, but in four cases the animals tested falsely positive owing to nonspecific staining. Immunohistochemistry staining on ear notch biopsies is thus a reliable diagnostic method to identify persistently infected animals with BVDV, but the pathologist should be aware of nonspecific positive staining.

Multiple diagnostic tests to identify cattle with Bovine viral diarrhea virus and duration of positive test results in persistently infected cattle

Several tests for Bovine viral diarrhea virus (BVDV) were applied to samples collected monthly from December 20, 2005, through November 27, 2006 (day 0 to day 342) from 12 persistently infected (PI) cattle with BVDV subtypes found in US cattle: BVDV-1a, BVDV-1b, and BVDV-2a. The samples included clotted blood for serum, nasal swabs, and fresh and formalin-fixed ear notches. The tests were as follows: titration of infectious virus in serum and nasal swabs; antigen-capture (AC) enzyme-linked immunosorbent assay (ELISA), or ACE, on serum, nasal swabs, and fresh ear notches; gel-based polymerase chain reaction (PCR) testing of serum, nasal swabs, and fresh ear notches; immunohistochemical (IHC) testing of formalin-fixed ear notches; and serologic testing for BVDV antibodies in serum. Of the 12 animals starting the study, 3 died with mucosal disease. The ACE and IHC tests on ear notches had positive results throughout the study, as did the ACE and PCR tests on serum. There was detectable virus in nasal swabs from all the cattle throughout the study except for a few samples that were toxic to cell cultures. The serum had a virus titer > or = log(10) 1.60 in all samples from all the cattle except for 3 collections from 1 animal. Although there were several equivocal results, the PCR test most often had positive results. The BVDV antibodies were due to vaccination or exposure to heterologous strains and did not appear to interfere with any BVDV test. These findings illustrate that PI cattle may be identified by several tests, but differentiation of PI cattle from cattle with acute BVDV infection requires additional testing, especially of blood samples and nasal swabs positive on initial testing. Also, calves PI with BVDV are continual shedders of infectious virus, as shown by the infectivity of nasal swabs over the 11-mo study.