Impact of three inactivated bovine viral diarrhoea virus vaccines on bulk milk p80 (NS3) ELISA test results in dairy herds

Exploring viral diversity and metagenomics in livestock: insights into disease emergence and spillover risks in cattle

Cattle have a significant impact on human societies in terms of both economics and health. Viral infections pose a relevant problem as they directly or indirectly disrupt the balance within cattle populations. This has negative consequences at the economic level for producers and territories, and also jeopardizes human health through the transmission of zoonotic diseases that can escalate into outbreaks or pandemics. To establish prevention strategies and control measures at various levels (animal, farm, region, or global), it is crucial to identify the viral agents present in animals. Various techniques, including virus isolation, serological tests, and molecular techniques like PCR, are typically employed for this purpose. However, these techniques have two major drawbacks: they are ineffective for non-culturable viruses, and they only detect a small fraction of the viruses present. In contrast, metagenomics offers a promising approach by providing a comprehensive and unbiased analysis for detecting all viruses in a given sample. It has the potential to identify rare or novel infectious agents promptly and establish a baseline of healthy animals. Nevertheless, the routine application of viral metagenomics for epidemiological surveillance and diagnostics faces challenges related to socioeconomic variables, such as resource availability and space dedicated to metagenomics, as well as the lack of standardized protocols and resulting heterogeneity in presenting results. This review aims to provide an overview of the current knowledge and prospects for using viral metagenomics to detect and identify viruses in cattle raised for livestock, while discussing the epidemiological and clinical implications.

Milk as a diagnostic fluid to monitor viral diseases in dairy cattle

BACKGROUND

Infectious viral diseases in dairy cattle have substantial implications for milk production, quality and overall animal health. Diagnostic tools providing reliable results are crucial for effective disease control at the farm and industry level. Pooled or bulk tank milk (BTM) can be used as a cost-effective aggregate sample to assess herd disease status in dairy farms.

FINDINGS

Detection of pathogens or specific antibodies in milk can be used for monitoring endemic diseases within-farm, region or country-level disease surveillance and to make informed decisions on farm management. The suitability of assays applied to pooled milk samples relies on validation data of fit-for-purpose tests to design an optimal testing strategy. Diverse approaches and variable scope of studies determining test accuracy need to be critically appraised before sourcing the parameters to design sampling strategies and interpreting surveys. Determining if BTM or pooled milk is the best approach for a disease management programme should carefully consider several aspects that will impact the accuracy and interpretation, for example, the size of the lactating herd, the risk of infection in the lactating and non-lactating groups, the expected within-herd prevalence, the duration of infection, the duration and concentration of antibodies in milk and use of vaccination.

CONCLUSIONS

There are examples of tests on BTM samples providing efficient assessments of the herd disease status and supporting disease control programmes for viral diseases. However, challenges arise in pooled milk testing due to the need for accurate estimates of the imperfect sensitivity and specificity of the assays. Integration of new biotechnologies could enhance multiplexing and data interpretation for comprehensive surveillance. The development of highly sensitive assays is necessary to meet the demands of larger dairy herds and improve disease detection and assessment.

A scoping review of the testing of bulk tank milk to detect nonbacterial pathogens or herd exposure to nonbacterial pathogens in dairy cattle

In this scoping review, we characterized the literature reporting on the testing of bulk milk samples to detect microorganisms other than bacteria that can cause diseases in dairy cattle, including viruses, helminths, algae, and protozoa. A search strategy was completed by screening databases, conference proceedings, animal health agency websites, disease surveillance program websites, and handbooks of cattle-related diagnostic tests for potentially relevant articles. Two reviewers independently screened articles in English, Portuguese, or Spanish; original studies reporting on the testing of farm-level, unprocessed bulk milk samples for presence of pathogens or specific antibodies against agents other than bacteria that can cause diseases in cows were retained. From all studies, we used spreadsheets to extract relevant information, including pathogen screened, test used, and country of origin of bulk milk samples. Additionally, for studies reporting sufficient data to estimate test characteristics, we extracted detailed information about herd eligibility, testing protocol, and herd-level infection definition. A total of 8,829 records were identified, from which 1,592 were retained and assessed for eligibility, and 306 were included. Bovine viral diarrhea virus, Fasciola hepatica, Ostertagia ostertagi, and bovine herpesvirus 1 were the most frequently screened agents, reported from 107, 45, 45, and 33 studies, respectively. Sensitivity of bulk milk ELISA to detect herds with animals infected by bovine herpesvirus 1 ranged from 2 to 100%, and was affected mostly by antigen selection, cut-off adopted, herd vaccination status, and seroprevalence of lactating cows. Bulk milk ELISA had very high specificity to detect herds free of bovine leukemia virus, and varying sensitivity to detect herds with infected animals, which depended on the within-herd seroprevalence of lactating cattle. As for bovine viral diarrhea virus, in general, the sensitivity of bulk milk ELISA was moderate to high (>80%) when infection status was defined based on presence of persistently infected cattle or a high proportion of seropositive lactating cattle. Nevertheless, bulk milk ELISA was not able to distinguish infected and noninfected herds based on presence of seropositive unvaccinated weanlings. The PCR or quantitative PCR protocols employed had very low sensitivities (<40%) and very high specificities (>95%) to classify bovine viral diarrhea virus infection status of dairy herds. Sensitivity and specificity of bulk milk ELISA to classify herds with regards to presence of F. hepatica- or O. ostertagi-parasitized cattle were generally high and driven mostly by the definition of herd infection status. Conversely, bulk milk ELISA demonstrated varying characteristics to detect herds with or without Dictyocaulus viviparus-parasitized cattle, depending primarily on the antigen selected and presence of cattle with clinical signs of lungworm infection.

Efficacy and durability of bovine virus diarrhea (BVD) virus killed vaccine adjuvanted with monolaurin

The bovine virus diarrhea virus (BVDV) causes reproductive, enteric, and respiratory diseases. Vaccination is essential in increasing herd resistance to BVDV spread. The selection of an adjuvant is an important factor in the success of the vaccination process. Monolaurin or glycerol monolaurate is a safe compound with an immunomodulatory effect. This study aimed to evaluate the efficacy of monolaurin as a novel adjuvant. This was examined through the preparation of an inactivated BVDV (NADL strain) vaccine adjuvanted with different concentrations of monolaurin and compared with the registered available locally prepared polyvalent vaccine (Pneumo-4) containing BVD (NADL strain), BoHV-1 (Abou Hammad strain), BPI3 (strain 45), and BRSV (strain 375L), and adjuvanted with aluminum hydroxide gel. The inactivated BVDV vaccine was prepared using three concentrations, 0.5%, 1%, and 2%, from monolaurin as adjuvants. A potency test was performed on five groups of animals. The first group, which did not receive vaccination, served as a control group while three other groups were vaccinated using the prepared vaccines. The fifth group received the Pneumo-4 vaccine. Vaccination response was monitored by measuring viral neutralizing antibodies using enzyme-linked immunosorbent assay (ELISA). It was found that the BVD inactivated vaccine with 1% and 2% monolaurin elicited higher neutralizing antibodies that have longer-lasting effects (nine months) with no reaction at the injection site in comparison to the commercial vaccine adjuvanted by aluminum hydroxide gel.

To Vaccinate or Not: Impact of Bovine Viral Diarrhoea in French Cow-Calf Herds

Bovine viral diarrhoea (BVD) remains an issue despite control programs implemented worldwide. Virus introduction can occur through contacts with neighbouring herds. Vaccination can locally protect exposed herds. However, virus spread depends on herd characteristics, which may impair vaccination efficiency. Using a within-herd epidemiological model, we compared three French cow-calf farming systems named by their main breed: Charolaise, Limousine, and Blonde d’Aquitaine. We assessed vaccination strategies of breeding females assuming two possible protections: against infection or against vertical transmission. Four commercial vaccines were considered: Bovilis^®, Bovela^®, Rispoval^®, and Mucosiffa^®. We tested various virus introduction frequency in a naïve herd. We calculated BVD economic impact and vaccination reward. In Charolaise, BVD economic impact was 113€ per cow over 5 years after virus introduction. Irrespective of the vaccine and for a high enough risk of introduction, the yearly expected reward was 0.80€ per invested euro per cow. Vaccination should not be stopped before herd exposure has been decreased. In contrast, the reward was almost nil in Blonde d’Aquitaine and Limousine. This highlights the importance of accounting for herd specificities to assess BVD impact and vaccination efficiency. To guide farmers’ vaccination decisions against BVD, we transformed this model into a French decision support tool.

Temporal trends in bulk tank milk antibody ELISA and PCR test results for bovine viral diarrhoea in New Zealand pastoral dairy herds

Aims: To describe temporal trends in bulk milk antibody ELISA and PCR testing for bovine viral diarrhoea (BVD) in New Zealand pastoral dairy herds and to assess the use of historical accession data to predict herd-level BVD incursions. Methods: Data on all diagnostic testing of bulk milk for BVD performed by the Livestock Improvement Corporation (Hamilton, NZ) over eight lactation seasons from 1 June 2010 to 31 May 2018 were analysed. This included anonymised herd identification, geographic location, herd size, sample collection date, sample to positive (S/P) ratio for antibody ELISA results, and cycle threshold values for PCR detecting viral RNA. Multivariable logistic regression was used to explore the relationship between historical accession data and the risk of herds having at least one positive bulk milk PCR test result in the 2017 season. Results: There were 156,034 bulk milk BVD diagnostic testing accessions for 10,495 uniquely identified dairy herds over the 8-season period. The prevalence of tested herds with at least one positive bulk milk PCR test result decreased from 14.6% (407/2,786) in the 2010 season to 5.6% (355/6,309) in the 2017 season with similarly marked declines in S/P ratios. In the 2017 season, 2,961/6,309 (46.9%) herds had S/P ratios greater than the 0.75 cut-off value indicating recent or active BVD virus transmission within the herd while 1,422/6,309 (22.5%) herds were classified as having negative or low S/P ratios. Herds that cleared BVD from the milking herd experienced a mean decline in S/P ratio of 0.11 units per year (min 0.05; max 0.18). In the multivariable analysis, the overall incidence risk of herds experiencing a BVD incursion in the 2017 season was 3.8% (146/3,848) and there were three significant predictors in the final model: herd size, PCR status in the 2014 season, and change in S/P ratio between the 2014 and 2015 seasons. The area under the receiver operating curve for the final model was 0.695 indicating poor discrimination. Conclusions and clinical relevance: The prevalence of dairy herds in New Zealand with positive bulk milk PCR test results and high S/P ratios has decreased over time, suggesting fewer herds are actively infected with BVD and that herd immunity may also be declining. Although monitoring trends in bulk milk test results provides useful information on changes in individual herd status, it is difficult to accurately predict when new incursions will occur and farmers should continue to maintain good biosecurity.

Genetic analysis of NS5B gene from bovine viral diarrhea virus-infected cattle in Central and East Java, Indonesia

Background and Aim:

A previous study divided Indonesian bovine viral diarrhea virus (BVDV)-1 into subgenotypes BVDV-1a to BVDV-1d based on the partial NS5B gene using strain Bega as reference for BVDV-1a. In fact, it is clustered into BVDV-1c with strain Bega-like Australia. BVDV genotyping has been done on isolates from Jakarta, West and Central Java, but East Java isolates have not been genotyped. This study aimed to analyze genetic variability and amino acid residues in the nucleotide-binding pocket of the NS5B gene from infected cattle.

Materials and Methods:

Samples were obtained from the Sera Bank originating from active and passive surveillance of cattle that had been tested for BVDV antigen from 2013 to 2017. Detection of the p80 antibody and BVDV genotyping was carried out using ELISA and nested-multiplex-polymerase chain reaction (PCR), respectively. We defined 15 nested PCR products for partial sequencing of NS5B. Those field samples were selected from each location and year using proportional calculation as a representative sample. Homological and phylogenetic analyses of the partial NS5B gene were performed using BLAST and MEGA version 6.

Results:

Based on the phylogenetic tree analysis using 360 nucleotides as the partial NS5B gene, Indonesian BVDV-1 isolates from Central and East Java were subdivided to BVDV-1a (n=9), BVDV-1b (n=1), and BVDV-1c (n=5). In the present study, the homology of BVDV subgenotype -1a, -1b, and -1c was compared to the BVDV GenBank data and found 90-93%, 93%, and 92-95% respectively with the average pairwise distance of 0.207. A point mutation was shown at R283K of all BVDV isolates based on the sequence of three amino acid residues R283, R285, and I287 in the nucleotide-binding pocket as a part of the encoded RNA-dependent RNA polymerase.

Conclusion:

This study revealed the genetic variability of BVDV infecting cattle in Central Java and East Java, Indonesia, the subtypes BVDV-1a, BVDV-1b, BVDV-1c, and a point mutation at the R283K residue.

Assessing the use of diagnostic laboratory accession data to support national bovine viral diarrhoea control in New Zealand

Aims: To assess the suitability of using existing national diagnostic laboratory testing data to support national bovine viral diarrhoea (BVD) research, surveillance, and control in New Zealand. Methods: Data on laboratory accessions for BVD diagnostic testing in New Zealand from 1 January 2015 to 31 December 2017 were provided by four commercial veterinary diagnostic companies. The data were integrated into a single dataset containing the unique accession number, sample submission date, farm location (territorial authority level), test type (bulk milk antibody-ELISA, bulk milk PCR, serum antibody-ELISA, blood/serum/tissue antigen-ELISA, or blood/serum/tissue PCR), and test results. Estimates for the number of registered cattle farms in each territorial authority were generated from the National Animal Identification and Tracing database. Results were summarised for July 2015 to June 2016 and July 2016 to June 2017. Results: There was a total of 59,007 unique BVD diagnostic test accessions including 39,920 (67.6%) for bulk milk antibody-ELISA, 27,832 (47.2%) for bulk milk PCR, 3,229 (5.5%) for serum antibody-ELISA, 9,132 (15.5%) for blood/serum/tissue antigen-ELISA, and 7,122 (12.1%) for blood/serum/tissue PCR. Of the 17,946 accessions for blood/serum/tissue samples, 4,316 (24.0%) were missing the herd production type and 6,678 (37.2%) were missing the animals age. Approximately 7,000/10,958 (65%) dairy herds and 1,600/43,611 (4%) beef herds were conducting annual BVD screening tests. In 2016/2017, the prevalence of accessions with ≥1 BVD-positive result was 40.6% for bulk milk antibody, 6.4% for bulk milk PCR, 45.6% for serum antibody, and 9.8% for blood/serum/tissue antigen-ELISA or PCR tests. There was substantial regional variation in both the percentage of herds testing for BVD and the prevalence of positive accessions. Following pooled serum antibody-ELISA, only 175/604 (29.0%) beef herds and 177/566 (31.3%) dairy herds had recorded follow-up testing. Conclusions and Clinical Relevance: Laboratory diagnostic accession data has the potential to provide valuable insights about BVD epidemiology in New Zealand, but there are significant limitations in the data collected and discrepancies in the different systems that each laboratory uses to measure, interpret, and record diagnostic data. There is a strong need to develop a more consistent national system for recording and sharing BVD test results to support BVD management at farm and industry levels. Abbreviations: BVD: Bovine viral diarrhoea; Ct: Cycle threshold; NAIT: National Animal Identification and Tracing; NZVP: New Zealand Veterinary Pathology; PI: Persistently infected; S/P: Sample to positive control.

Evaluation of 16 commercial antibody ELISAs for the detection of bovine viral diarrhea virus–specific antibodies in serum and milk using well-characterized sample panels

We performed a thorough fit-for-purpose evaluation of commercial ELISAs for the detection of bovine viral diarrhea virus (BVDV)-specific antibodies in serum and in milk by testing 2 panels of well-characterized serum and milk samples. Sixteen ELISAs from 9 different manufacturers, available on the Belgian market at the time of our study, were assessed for their diagnostic and analytical sensitivity (DSe and ASe, respectively), diagnostic specificity (DSp), and repeatability relative to the virus neutralization (VN) test considered to be the gold standard assay. Using serum as a matrix, DSe was much lower for competitive (c)ELISAs (min. 45%, max. 65%) than for indirect (i)ELISAs (min. 85%, max. 100%), partly because of the lower detection of positive samples from vaccinated animals included in the panel. ASe was also better for iELISAs; DSp was >95% for all but 2 ELISAs. Repeatability, expressed as coefficients of variation (CV) of optical densities, was generally good, although 3 ELISAs had a mean CV >10%. With milk samples, as observed for serum, DSe was lower for cELISAs (min. 57%, max. 75%) than for iELISAs (min. 61%, max. 89%), and DSp was high for all ELISAs (min. 94%, max. 100%). Both DSe and ASe were lower when testing milk samples compared to serum samples. These results confirm that serologic monitoring of BVDV-free herds should be performed using serum samples of unvaccinated animals to avoid interference of vaccination and to maximize the chance of detecting seroconversion linked to BVDV infection. Further investigations using a larger collection of field samples are recommended.

Selection and characterization of specific nanobody against bovine virus diarrhea virus (BVDV) E2 protein

Bovine viral diarrhea-mucosal disease (BVD-MD) is caused by bovine viral diarrhea virus (BVDV), and results in abortion, stillbirth, and fetal malformation in cows. Here, we constructed the phage display vector pCANTAB 5E-VHH and then transformed it into Escherichia coli TG1-competent cells, to construct an initial anti-BVDV nanobody gene library. We obtained a BVDV-E2 antigen epitope bait protein by prokaryotic expression using the nucleotide sequence of the E2 gene of the BVDV-NADL strain published in GenBank. Phage display was used to screen the anti-BVDV nanobody gene library. We successfully constructed a high quality phage display nanobody library, with an initial library capacity of 4.32×105. After the rescue of helper phage, the titer of the phage display nanobody library was 1.3×1011. The BVDV-E2 protein was then expressed in Escherichia coli (DE3), and a 49.5 kDa band was observed with SDS-PAGE analysis that was consistent with the expected nanobody size. Thus, we were able to isolate one nanobody that exhibits high affinity and specificity against BVDV using phage display techniques. This isolated nanobody was then used in Enzyme Linked Immunosorbent Assay and qRT-PCR, and ELISA analyses of BVDV infection of MDBK cells indicated that the nanobodies exhibited good antiviral effect.