Efficacy of a live bovine herpesvirus type 1 marker vaccine under field conditions in three countries

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.

Assessment of Different Infectious Bovine Rhinotracheitis Marker Vaccines in Calves

Three commercially available infectious bovine rhinotracheitis (IBR) live marker vaccines were evaluated for their ability to provide clinical protection to vaccinated calves against wild-type (wt) Bovine alphaherpesvirus-1 (BoHV-1) challenge and their possible effect on wt BoHV-1 latency reactivation following the challenge. On 35 post-vaccination days (PVDs), all animals were challenged with wt BoHV-1. Only the calves in the control group developed severe forms of IBR. The reactivation of latent BoHV-1 was induced by dexamethasone (DMS) treatment on 28 post-challenge days (PCDs). All animals showed IBR clinical signs on three post-DMS treatment days (PDTDs). On PVD 14, all vaccinated animals developed neutralizing antibodies (NAs), whereas in control animals, the NAs appeared post-challenge. The positivity for glycoprotein-B (gB) was detected using real-time polymerase chain reactions in all animals from PCDs 1 to 7. In contrast, the gB-positivity was observed in the immunized calves from PDTDs 3 to 10. Positive expression of gD and gE was observed in nasal swabs of all calves on PDTD 7. These findings suggested that the IBR marker vaccines evaluated in this study protected against wt BoHV-1-induced disease but not against wt BoHV-1-induced latency reactivation, indicating the necessity of developing new products to protect animals from wt BoHV-1-induced latency.

Control programs for infectious bovine rhinotracheitis (IBR) in European countries: an overview

Infectious bovine rhinotracheitis (IBR), caused by Bovine alphaherpesvirus 1 (BoHV-1), is a disease of cattle responsible for significant economic losses worldwide. IBR is under certain communitarian regulations. Every member state can approve its own national IBR control program for the entire territory – or part of it – and can demand additional guarantees for bovids destined to its territory; therefore, every member state can be officially declared as entirely or partly IBR-free. The aim of this review is to provide an overview of IBR control and eradication programs in European countries. BoHV-1 control schemes were first introduced in the late 1970s, mainly in Northern and Central Europe. Depending on the seroprevalence rate, control strategies rely on identification and removal of seropositive animals or the use of glycoprotein E (gE)-deleted marker vaccines in infected herds. The implementation of a novel law for disease eradication at the EU level and of a European IBR data flow could make the goal of IBR eradication in all European countries easier to achieve.

Impact of Overuse and Sexually Transmitted Infections on Seminal Parameters of Extensively Managed Bulls

Natural service remains the main breeding method in extensively managed beef herds. Although the bull might be the most important factor in determining herd fertility, its importance has been largely overlooked, focusing instead on female fertility. Management of the bull is critical to maximize the opportunities for cow conception. Infectious bovine rhinotracheitis (IBR) and bovine viral diarrhea (BVD) are infections associated with reduced conception rates. This study aimed to determine the effect of both IBR and BVD infection, and bull: cow ratio on seminal parameters in the bull and herd fertility. The presence of antibodies to IBR and BVD, seminal parameters (volume, concentration, mass, and progressive motility), and herd fertility were analyzed in 158 extensively managed bulls. Sperm concentration and mass motility, as well as herd fertility, were significantly lower in BVD-positive bulls. No significant differences were found between IBR-positive and -negative bulls in any reproductive parameter. Sperm concentration was negatively affected by BVD infection in both Charolais and Limousin bulls, whereas mass motility and herd fertility were reduced in Limousin bulls only. No differences were observed in the cow: bull ratio between BVD+ and BVD- bulls. A significant negative correlation was detected between the number of cows per bull and herd fertility, which was negatively affected when herds had more than 40 cows per bull. In conclusion, BVD and bull overuse negatively affect the reproductive performance of the herd.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): infectious bovine rhinotracheitis (IBR)

Infectious bovine rhinotracheitis (IBR) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of IBR to be listed, Article 9 for the categorisation of IBR according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to IBR. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, IBR can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria in Sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The assessment here performed on compliance with the criteria as in Section 3 of Annex IV referred to in point (c) of Article 9(1) is inconclusive. The animal species to be listed for IBR according to Article 8(3) criteria belong to the order Artiodactyla.

Bovine herpesvirus glycoprotein D: a review of its structural characteristics and applications in vaccinology

The viral envelope glycoprotein D from bovine herpesviruses 1 and 5 (BoHV-1 and -5), two important pathogens of cattle, is a major component of the virion and plays a critical role in the pathogenesis of herpesviruses. Glycoprotein D is essential for virus penetration into permissive cells and thus is a major target for virus neutralizing antibodies during infection. In view of its role in the induction of protective immunity, gD has been tested in new vaccine development strategies against both viruses. Subunit, DNA and vectored vaccine candidates have been developed using this glycoprotein as the primary antigen, demonstrating that gD has the capacity to induce robust virus neutralizing antibodies and strong cell-mediated immune responses, as well as protection from clinical symptoms, in target species. This review highlights the structural and functional characteristics of BoHV-1, BoHV-5 and where appropriate, Human herpesvirus gD, as well as its role in viral entry and interactions with host cell receptors. Furthermore, the interactions of gD with the host immune system are discussed. Finally, the application of this glycoprotein in new vaccine design is reviewed, taking its structural and functional characteristics into consideration.

Epidemiology and control of bovine herpesvirus 1 infection in Europe

Bovine herpesvirus 1 (BHV-1) causes infectious bovine rhinotracheitis (IBR), infectious pustular vulvovaginitis, abortion and balanoposthitis, as well as neurological and systemic disease in cattle. The virus is endemic in cattle populations worldwide although in Europe six countries and several regions in other countries have achieved 'IBR-free' status by implementing control measures. According to European Union (EU) directives, all member states must comply with specific requirements related to BHV-1 infection status in semen and embryos. The requirement that 'IBR-free' states restrict the importation of cattle from endemically infected regions has motivated several European countries to instigate disease eradication programmes. Despite such control measures within the EU, outbreaks of IBR persist in 'IBR-free' states contiguous with infected countries. This review presents a summary of recent research on the epidemiology of BHV-1, highlights the control measures and surveillance systems in place, and discusses the challenges facing eradication schemes.

Aspects of bovine herpesvirus-1 infection in dairy and beef herds in the Republic of Ireland

Background

Infection with bovine herpesvirus-1 (BHV-1) causes a wide range of disease manifestations, including respiratory disease and abortion, with world-wide distribution. The primary objective of the present study was to describe aspects of BHV-1 infection and control on Irish farms, including herd-level seroprevalence (based on pooled sera) and vaccine usage.

Methods

The characteristics of a diagnostic indirect BHV-1 antibody ELISA test when used on serum pools were evaluated using laboratory replicates for use in the seroprevalence study. The output from this indirect ELISA was expressed as a percentage positivity (PP) value. A proposed cut off (PCO) PP was applied in a cross-sectional study of a stratified random sample of 1,175 Irish dairy and beef cattle herds in 2009, using serum pools, to estimate herd seroprevalence. The study was observational, based primarily on the analysis of existing samples, and only aggregated results were reported. For these reasons, ethical approval was not required. Bulk milk samples from a subset of 111 dairy herds were analysed using the same ELISA. Information regarding vaccine usage was determined in a telephone survey.

Results

A PCO PP of 7.88% was determined to give 97.1% sensitivity and 100% specificity relative to the use of the ELISA on individual sera giving maximization of the prevalence independent Youden's index, on receiver operating characteristics analysis of replicate results. The herd-level BHV-1 seroprevalence was 74.9% (95% CI - 69.9%-79.8%), with no significant difference between dairy and beef herds. 95.5% agreement in herd classification was found between bulk milk and serum pools. Only 1.8 percent of farmers used BHV-1 marker vaccine, 80% of which was live while 75% of vaccinated herds were dairy.

A significant association was found between herd size (quartiles) and seroprevalence (quartiles).

Conclusions

The results from this study indicate BHV-1 infection is endemic, although BHV-1 vaccines are rarely used, in the cattle population in Ireland.