Serological Cross-Reactivity Between Bovine alphaherpesvirus 2 and Bovine alphaherpesvirus 1 in a gB-ELISA: A Case Report in Italy

Enhanced immune response with baculovirus-expressed BoHV-1 glycoprotein D in vaccine development

Bovine herpesvirus 1 (BoHV-1), a significant pathogen in the alpha-herpesvirus subfamily, primarily infects cattle and causes the upper respiratory disease known as infectious bovine rhinotracheitis (IBR). In silico studies evaluated the BoHV-1 D protein to be non-allergenic, non-toxic, and highly antigenic, highlighting its potential as an antigen for vaccine development. Therefore, this study aimed to evaluate the efficacy of a subunit vaccine using the ectodomain of glycoprotein D (gD34-380) as an antigen. The truncated gD was successfully cloned and expressed in both Escherichia coli (E. coli, termed EgD) and baculovirus (termed BgD) systems, with expected molecular weights of 65 kDa and 50 kDa, respectively. For the vaccine formulation, the gD proteins were used either alone or in combination with in-house inactivated BoHV-1. Vaccination of mice and bovines showed that baculovirus-expressed gD34-380 accelerated the antibody response. Moreover, the BgD-vaccinated group also showed significantly higher neutralizing antibody levels against BoHV-1 than the control group (p<0.0001). In conclusion, our study found that BgD from BoHV-1 can increase the immune response and enhance vaccine efficacy.

EAVLD 2024 - 7th Congress of the European Association of Veterinary Laboratory Diagnosticians

This abstract book contains the abstracts presented at the 7th Congress of the European Association of Veterinary Laboratory Diagnosticians.

Infectious bovine rhinotracheitis: Unveiling the hidden threat to livestock productivity and global trade

An infectious disease called infectious bovine rhinotracheitis (IBR) can lead to a number of disorders affecting cattle's respiratory system. The disease is caused by bovine alphaherpesvirus type 1 (BoAHV-1). Based on antigenic and genetic characteristics, BoAHV-1 strains are divided into subtypes 1.1, 1.2a, 1.2b, and 1.3. IBR is currently widespread throughout the world, with the exception of a few nations that have achieved eradication. The most significant characteristic of this illness is that, after a clinical or subclinical infection, the virus typically establishes a latent condition that can later be reactivated in the presence of stress, immunosuppressive conditions/substances, or other diseases. Primarily, the virus spreads by direct or indirect contact between animals. It may also be transmitted via the reproductive system, causing infectious balanoposthitis or vulvovaginitis. Most virus subtypes are associated with reproductive failure, such as fetal or embryonic resorption and abortions. The virus may also be transmitted through semen, which could lead to genital transfer. Bovine herpesvirus type 1 (BoHV-1) infection produces a variety of lesions. Lesion in the mucosal surface usually consists of white necrotic material. Regular methods for diagnosing BoHV-1 infections include isolation in cell culture, enzyme linked immunosorbent assay, virus neutralisation test, and methods based on identification of nucleic acids, like PCR. The interplay of several host, pathogen, environmental, and management factors affects the spread of IBR. Through its impacts on health and fitness, IBR can lead to production losses. In order to minimize the severity of clinical signs and stop the infection from spreading, the veterinarian may advise that sick or at-risk animals be placed under immediate isolation and vaccinated (such as intranasal vaccination, including the use of both killed and live attenuated virus vaccines) as soon as an IBR diagnosis is obtained.

The biology and development of vaccines for bovine alphaherpesvirus 1

Bovine alphaherpesvirus type 1 (BoAHV-1) infections lead to compromised herd health and significantly reduced productivity of affected cattle. While BoAHV-1 may cause rhinotracheitis, conjunctivitis, genital infections, and abortions, respiratory tract infections constitute the predominant clinical disease. Immune suppression induced by BoAHV-1 may contribute to co-infections initiating the bovine respiratory disease complex. In this review, the emphasis is to recapitulate the biology and the vaccine technologies currently in use and in development for BoAHV-1, and to discuss the major limitations. Studies on the life cycle and host interactions of BoAHV-1 have resulted in the identification of virulence factors. While several vaccine types, such as vectored vaccines and subunit vaccines, are under investigation, modified live and inactivated BoAHV-1 vaccines are still most frequently used in most areas of the world, whereas attenuated and inactivated marker vaccines are in use in Europe. The knowledge gained from studies on the biology of BoAHV-1 can form a basis for the rational design of future vaccines.

Cattle exposure to bubaline herpesvirus (BuHV-1) in Southern Italy: A hidden threat for IBR eradication?

There is sufficient evidence that both bovine herpesvirus (BoHV-1) and bubaline herpesvirus (BuHV-1) can overcome the species barrier represented by their respective hosts, cattle and buffalo. Although several studies have focused on the impact of BoHV-1 on buffalo, little is known about the impact of BuHV-1 on cattle. In this work, we evaluated the seroprevalence of BuHV-1 in the cattle population in an area where intensive buffalo farming is highly developed (Campania region, Italy). BuHV-1 seroprevalence of cattle sampled in this study was estimated to be 21.4% using a specific commercial ELISA for the detection of antibodies against glycoprotein E of the virus. Risk factor assessment by univariate analysis revealed a correlation between housing type and higher prevalence. Similarly, cattle housed with buffalo and adult animals had a higher likelihood of being seropositive. BoHV-1 vaccination did not prove to be a protective factor against BuHV-1 exposure. The role of age, grazing, and co-living with buffalo in influencing BuHV-1 exposure was also confirmed by multivariate analysis. All BuHV-1 positive animals were also tested with cross-serum neutralization aimed at evaluating the specific antibody titers against BoHV-1 and BuHV-1. We, therefore, assessed the potential cross-reaction between BoHV-1 and BuHV-1, the co-infection rate, and the agreement of the assays used. This study described the presence of BuHV-1 in the cattle population of the Campania region (Italy) and indicated the requirement to take BuHV-1 into consideration for any measures and control and/or eradication plans to be applied against BoHV-1.

Infectious Bovine Rhinotracheitis Post-Eradication Program in the Autonomous Province of Bolzano, Italy: A Retrospective Study on Potential Bovine Herpesvirus Type 2 Cross-Reactivity

Bovine alphaherpesviruses, BoAHV, can cause respiratory, genital and neurological disorders. In particular, bovine alphaherpesvirus type 1 (BoAHV1) is one of the most significant ruminant pathogens worldwide and it can heavily damage the livestock industry. BoAHV1 can cause infectious bovine rhinotracheitis (IBR) along with fertility disorders. Bovine alphaherpesvirus type 2 (BoAHV2) can cause two different conditions as well: pseudo-lumpy skin disease (PSLD) and bovine herpetic mammillitis (BHM). The autonomous province of Bolzano (Italy) has adopted several strategies to control and eradicate IBR, and it was declared in 2000 to be IBR-free by the European Commission. Since 2001, a post-eradication monitoring program has overseen the serological analysis of bulk milk and, in the presence of a positive result, a follow-up examination is performed on the individual blood serum of all bovines older than 24 months that belong to bulk milk-positive herds. Despite the detection of positives in both bulk milk and serum samples, South Tyrol has been declared IBR-free, as these positives have never been confirmed through seroneutralization. Between 2014 and 2022, approximately 41,000 bulk milk (averaging 4300 samples/year) and 3229 serum samples were tested for BoAHV1. The aim of this study was to evaluate the post-eradication program for IBR with a particular focus on the potential cross-reactivity with BoAHV2; for this reason, serum samples were also tested for BoAHV2 antibodies. This study could be of great importance for those countries that submit herds to an IBR monitoring and eradication program; performing further analyses to confirm and explain false positive outcomes would increase the reliability of the obtained results.

Evaluation of an Immunization Protocol Using Bovine Alphaherpesvirus 1 gE-Deleted Marker Vaccines against Bubaline Alphaherpesvirus 1 in Water Buffaloes

European regulations on the control of infectious diseases provide measures to control Bovine alphaherpesvirus 1 (BoHV-1) infection in both cattle and buffalo. Owing to the reported serological cross-reactivity between BoHV-1 and Bubaline alphaherpesvirus 1 (BuHV-1), we hypothesized a new immunization protocol using BoHV-1 gE-deleted marker vaccines could protect water buffalo against BuHV-1. Five water buffaloes devoid of BoHV-1/BuHV-1-neutralizing antibodies were immunized with two commercial BoHV-1 gE-deleted marker vaccines at 0, 30, 210, and 240 post-vaccination days (PVDs). Five additional water buffaloes were used as controls. At 270 PVD (0 post-challenge days (PCDs), all animals were challenged intranasally with wild-type (wt) BuHV-1. The vaccinated animals produced humoral immunity (HI) as early as PVD 30 whereas, in control animals, antibodies were detected on PCD 10. After challenge infection, HI significantly increased in vaccinated animals compared to that in controls. Real-time PCR for gB revealed viral shedding in vaccinated animals from PCDs 2 to 10. In contrast, positive results were observed from PCDs 2 to 15 in the unvaccinated control group. Although the findings indicated the possible protection capabilities of the tested protocol, these findings did not support its protective roles in water buffaloes against wt-BuHV-1.

A retrospective evaluation of pooled serum ELISA testing in the frame of the French eradication program for infectious bovine rhinotracheitis

Pooled serum testing using whole-virus indirect ELISA has been recently recognized as an official method for surveillance of bovine herpesvirus 1 (BoHV1) in cattle herds in Europe. In this study, a retrospective analysis of data from the French BoHV1 surveillance campaign 2018-2019, including 7434 BoHV1-free certified herds and 157 infected herds, was performed in order to evaluate the diagnostic specificity and sensitivity of two pooled serum indirect ELISAs (from IDEXX and IDVet), in comparison with individual testing by blocking ELISAs targeting the gB and gE proteins. Pooled serum testing showed a relative specificity higher than 97.5% and a detection rate of 100% since all gB+/gE+ samples were found in positive pools. At the herd level, no more than one false positive pool was observed in most of BoHV1-free certified herds, leading to a herd relative specificity of 85.1% and 86.0% for the IDEXX and IDVet pooled serum ELISAs, respectively. Among infected herds tested by pool sizes up to 10 sera (n = 122), 46% of herds were detected through pools of size 10 containing a single positive sample, 23% through pools of size 10 containing at least two positive samples, and 31% through pools of smaller sizes. A complementary study based on manually constituted pools revealed that at least one positive sample in 100% and 93.4% of herds could be detected individually by pools of size 10 with the IDEXX and IDVet ELISAs, respectively. However, pooled serum ELISAs were influenced by the level of individual reactivity, since pools composed of either one weak-positive sample or one gB+/gE- sample could yield negative results. Altogether, these results provided the first evidence that pooled serum testing (pool size up to 10) is a suitable strategy for surveillance of BoHV1-free cattle farms.

Validation of a Commercial Indirect ELISA Kit for the Detection of Bovine alphaherpesvirus1 (BoHV-1)-Specific Glycoprotein E Antibodies in Bulk Milk Samples of Dairy Cows

In this study, we validated a commercial indirect enzyme-linked immunosorbent assay (ELISA) to detect antibodies to glycoprotein E (gE) of Bovine alphaherpesvirus 1 (BoHV-1) in bulk milk (BM) samples using the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. The assay performance characteristics were evaluated using a panel of positive (n = 36) and negative (n = 80) samples with known infectious bovine rhinotracheitis (IBR) status. The assay showed adequate repeatability (within-run and between-run), with a coefficient of variability (CV%) of replicates below 30%; only two 1:40 diluted samples had a CV% above 20%. Additionally, an agreement analysis of the qualitative results of replicates led to a Gwet’s agreement coefficient of 0.99 (95% confidence interval (CI): 0.96−1.00, p < 0.001). The estimated diagnostic sensitivity (DSe) and diagnostic specificity (DSp) were 100% (95% CI: 90.3−100%) and 97.5% (95% CI: 91.3−99.7%), respectively. Overall, a good level of agreement was observed between the assay results and the true IBR status of samples (weighted Cohen’s κ: 0.96, 95% CI: 0.78−1.00). The findings demonstrate that the indirect ELISA kit validated here is an easy-to-use and economical method to differentiate infected and gE-deleted marker vaccine-immunised animals using BM samples.

Sero-diagnostic efficacy of various ELISA kits for diagnosis of infectious bovine rhinotracheitis (IBR) in cattle and buffaloes in India

Bovine alphaherpesvirus-1 (BoHV-1), the causative agent of infectious bovine rhinotracheitis (IBR), is an economically important viral pathogen affecting cattle and buffaloes. Serological assays are mostly used for detection of the antibodies, but variation has been detected in the diagnostic performances of the individual assay. In the present study, four commercially available ELISA kits {two indirect ELISA (kits A and B) and two blocking ELISA (kits C and D)} were evaluated for the detection of antibodies against BoHV-1 in Indian cattle and buffaloes (fitness of purpose). The diagnostic sensitivity (dsn) and specificity (dsp) of these kits were determined by three ways; considering virus neutralization test (VNT) as gold standard test, using pre-test information of the samples, and majority of tests. Screening of 200 known negative sera (124 cattle, 76 buffaloes) sourced from IBR free farms revealed gB based ELISA kits are more specific than the indirect ELISA kits. Testing of 125 known positive sera (81 cattle, 44 buffaloes) suggests kit B be most sensitive followed by kit C, A and D. Interestingly, kit D was found to be most sensitive for detection of vaccination-induced BoHV-1 antibodies followed by kit B. Similar trend were also observed in the limit of dilution experiment performed using known infected and vaccinated sera. VNT was found to be the most specific test and its use as the gold standard test revealed all kits to have more than 99 % sensitivity. All the ELISA kits could detect BoHV-1 specific antibodies in the IBR vaccinated calves as early as 11 days post-vaccination. In Kappa statistics, an almost perfect agreement between the ELISA kits was recorded. The overall performance of the kits in serodiagnosis of IBR as determined by the area under curve in ROC analysis was good.