The effect of formalin-inactivated vaccine on respiratory disease associated with bovine respiratory syncytial virus infection in calves

Global estimates on the reports of vaccine-associated myocarditis and pericarditis from 1969 to 2023: Findings with critical reanalysis from the WHO pharmacovigilance database

Due to the limitation of previous studies examining adverse reports of myocarditis and pericarditis associated with vaccines other than the COVID-19 vaccine, there are challenges in establishing a comprehensive understanding of vaccine safety on a global scale. Hence, the objective of this study was to examine the worldwide burden of vaccine-associated pericarditis and myocarditis and the vaccines associated with these indications. This study utilized the World Health Organization international pharmacovigilance database, from which records of vaccine-associated pericarditis and myocarditis between 1969 and 2023 were extracted (over 130 million reports). We calculated global reporting counts, reported odds ratios (RORs), and information components (ICs) to discern the association between 19 vaccines and the occurrence of pericarditis and myocarditis across 156 countries and territories. We identified 49 096 reports (male, n = 30 013) of vaccine-associated pericarditis and myocarditis among 73 590 reports of all-cause pericarditis and myocarditis. There has been a significant increase in reports of vaccine-related cardiac adverse events over time, with a noteworthy surge observed after 2020, attributed to cases of pericarditis associated with COVID-19 mRNA vaccines. Smallpox vaccines were associated with most pericarditis and myocarditis reports (ROR: 73.68 [95% CI, 67.79-80.10]; IC [IC0.25]: 6.05 [5.91]), followed by COVID-19 mRNA vaccine (37.77 [37.00-38.56]; 3.07 [3.05]), anthrax vaccine (25.54 [22.37-29.16]; 4.58 [4.35]), typhoid vaccine (6.17 [5.16-7.38]; 2.59 [2.29]), encephalitis vaccine (2.00 [1.48-2.71]; 0.99 [0.47]), influenza vaccine (1.87 [1.71-2.04]; 0.90 [0.75]), and Ad5-vectored COVID-19 vaccine (1.40 [1.34-1.46]; 0.46 [0.39]). Concerning age and sex-specific risks, reports of vaccine-associated pericarditis and myocarditis were more prevalent among males and in older age groups. The age group between 12 and 17 years exhibited significant sex disproportion. Most of these adverse events had a short time to onset (median time: 1 day) and fatality rate was 0.44%. Our analysis of global data revealed an increase in pericarditis and myocarditis reports associated with vaccines, particularly live vaccines like smallpox and anthrax, notably in young males. While these adverse events are generally rare and mild, caution is warranted, especially for healthcare workers, due to potential myocardial injury-related in-hospital mortality. Further study with validated reporting is crucial to enhance accuracy in evaluating the correlation between vaccines and cardiac conditions for preventive measures.

ChAd155-RSV vaccine is immunogenic and efficacious against bovine RSV infection-induced disease in young calves

Respiratory syncytial virus (RSV) infection causes a substantial lower-respiratory-tract disease burden in infants, constituting a global priority for vaccine development. We evaluated immunogenicity, safety and efficacy of a chimpanzee adenovirus (ChAd)-based vaccine candidate, ChAd155-RSV, in a bovine RSV (bRSV) challenge model. This model closely reproduces the pathogenesis/clinical manifestations of severe pediatric RSV disease. In seronegative calves, ChAd155-RSV elicits robust neutralizing antibody responses against human RSV. Two doses protect calves from clinical symptoms/lung pathological changes, and reduce nasal/lung virus loads after both a short (4-week) and a long (16-week) interval between last immunization and subsequent bRSV challenge. The one-dose regimen confers near-complete or significant protection after short-term or long-term intervals before challenge, respectively. The presence of pre-existing bRSV-antibodies does not affect short-term efficacy of the two-dose regimen. Immunized calves present no clinical signs of enhanced respiratory disease. Collectively, this supports the development of ChAd155-RSV as an RSV vaccine candidate for infants.

Efficacy of Bovine Respiratory Syncytial Virus Vaccines to Reduce Morbidity and Mortality in Calves Within Experimental Infection Models: A Systematic Review and Meta-Analysis

Producers and veterinarians commonly use vaccination as the main strategy to reduce the incidence of bovine respiratory syncytial virus (BRSV) infection in calves; however, supportive evidence of BRSV vaccination efficacy has been inconsistent in the literature. The objective of this meta-analysis was to evaluate data from controlled studies on the efficacy of commercially available BRSV vaccines on reducing calf morbidity and mortality after experimental infection with BRSV. A systematic review and meta-analysis was performed in BRSV experimental challenge studies that reported the efficacy of commercially available modified-live virus (MLV) and inactivated BRSV vaccines on protection against calf morbidity and mortality. The studies included in the analysis were randomized, controlled, clinical trials with clear definitions of calf morbidity and mortality. Risk ratios with 95% confidence intervals and forest plots were generated. Fourteen studies including 29 trials were selected for the analysis. Commercially available MLV BRSV vaccines reduced the risk of calf mortality after experimental infection with BRSV. Modified-live virus vaccines reduced the risk of morbidity in calves with absence of serum maternal antibodies at initial vaccination, but failed to demonstrate significant morbidity reduction when calves were vaccinated in the face of maternal immunity. Results from experimental challenge studies do not always represent the conditions of natural infection and caution should be used when making vaccine recommendations.

A Review of UK-Registered and Candidate Vaccines for Bovine Respiratory Disease

Vaccination is widely regarded as a cornerstone in animal or herd health and infectious disease management. Nineteen vaccines against the major pathogens implicated in bovine respiratory disease are registered for use in the UK by the Veterinary Medicines Directorate (VMD). However, despite annual prophylactic vaccination, bovine respiratory disease is still conservatively estimated to cost the UK economy approximately £80 million per annum. This review examines the vaccine types available, discusses the surrounding literature and scientific rationale of the limitations and assesses the potential of novel vaccine technologies.

Review on bovine respiratory syncytial virus and bovine parainfluenza - usual suspects in bovine respiratory disease - a narrative review

Bovine Respiratory Syncytial virus (BRSV) and Bovine Parainfluenza 3 virus (BPIV3) are closely related viruses involved in and both important pathogens within bovine respiratory disease (BRD), a major cause of morbidity with economic losses in cattle populations around the world. The two viruses share characteristics such as morphology and replication strategy with each other and with their counterparts in humans, HRSV and HPIV3. Therefore, BRSV and BPIV3 infections in cattle are considered useful animal models for HRSV and HPIV3 infections in humans.

The interaction between the viruses and the different branches of the host’s immune system is rather complex. Neutralizing antibodies seem to be a correlate of protection against severe disease, and cell-mediated immunity is thought to be essential for virus clearance following acute infection. On the other hand, the host’s immune response considerably contributes to the tissue damage in the upper respiratory tract.

BRSV and BPIV3 also have similar pathobiological and epidemiological features. Therefore, combination vaccines against both viruses are very common and a variety of traditional live attenuated and inactivated BRSV and BPIV3 vaccines are commercially available.

A Recombinant BCG Vaccine Is Safe and Immunogenic in Neonatal Calves and Reduces the Clinical Disease Caused by the Respiratory Syncytial Virus

The human respiratory syncytial virus (hRSV) constitutes a major health burden, causing millions of hospitalizations in children under five years old worldwide due to acute lower respiratory tract infections. Despite decades of research, licensed vaccines to prevent hRSV are not available. Development of vaccines against hRSV targeting young infants requires ruling out potential vaccine-enhanced disease presentations. To achieve this goal, vaccine testing in proper animal models is essential. A recombinant BCG vaccine that expresses the Nucleoprotein of hRSV (rBCG-N-hRSV) protects mice against hRSV infection, eliciting humoral and cellular immune protection. Further, this vaccine was shown to be safe and immunogenic in human adult volunteers. Here, we evaluated the safety, immunogenicity, and protective efficacy of the rBCG-N-hRSV vaccine in a neonatal bovine RSV calf infection model. Newborn, colostrum-replete Holstein calves were either vaccinated with rBCG-N-hRSV, WT-BCG, or left unvaccinated, and then inoculated via aerosol challenge with bRSV strain 375. Vaccination with rBCG-N-hRSV was safe and well-tolerated, with no systemic adverse effects. There was no evidence of vaccine-enhanced disease following bRSV challenge of rBCG-N-hRSV vaccinated animals, suggesting that the vaccine is safe for use in neonates. Vaccination increased virus-specific IgA and virus-neutralization activity in nasal fluid and increased the proliferation of virus- and BCG-specific CD4+ and CD8+ T cells in PBMCs and lymph nodes at 7dpi. Furthermore, rBCG-N-hRSV vaccinated calves developed reduced clinical disease as compared to unvaccinated control calves, although neither pathology nor viral burden were significantly reduced in the lungs. These results suggest that the rBCG-N-hRSV vaccine is safe in neonatal calves and induces protective humoral and cellular immunity against this respiratory virus. These data from a newborn animal model provide further support to the notion that this vaccine approach could be considered as a candidate for infant immunization against RSV.

NASYM, a live intranasal vaccine, protects young calves from bovine respiratory syncytial virus in the presence of maternal antibodies

BACKGROUND

Bovine respiratory syncytial virus (BRSV) is a major problem for cattle worldwide during their first year of life. The aim of the present study was to evaluate efficacy and longevity of immunity of a live vaccine (NASYM, HIPRA) in the presence of maternally derived antibodies (MDA).

METHOD

Calves (36) were distributed in four groups, based on MDA status and treatment. They received NASYM or a placebo at an early age (less than two weeks) by intranasal route. Eight weeks later, animals were challenged with the Asquith strain of BRSV. Efficacy was assessed by monitoring clinical signs and mortality, PaO₂ , virus shedding and lung lesions. The immunological response was evaluated by measuring IgG in serum and IgA in nasal secretions.

RESULTS

A reduction of mortality, lung lesions, shedding and a higher PaO₂ was achieved in NASYM vaccinated groups, independently of MDA status. An anamnestic IgG response was observed after challenge in vaccinated animals, both in MDA+ and MDA- groups. An IgA response was also observed in vaccinated animals after vaccination and challenge.

CONCLUSION

NASYM protected newborn calves with MDAs during the first 10 weeks of life, against a very virulent challenge that caused extensive pulmonary lesions and deaths in control animals, with just a single intranasal dose.

Applications of Nanovaccines for Disease Prevention in Cattle

Vaccines are one of the most important tools available to prevent and reduce the incidence of infectious diseases in cattle. Despite their availability and widespread use to combat many important pathogens impacting cattle, several of these products demonstrate variable efficacy and safety in the field, require multiple doses, or are unstable under field conditions. Recently, nanoparticle-based vaccine platforms (nanovaccines) have emerged as promising alternatives to more traditional vaccine platforms. In particular, polymer-based nanovaccines provide sustained release of antigen payloads, stabilize such payloads, and induce enhanced antibod- and cell-mediated immune responses, both systemically and locally. To improve vaccine administrative strategies and efficacy, they can be formulated to contain multiple antigenic payloads and have the ability to protect fragile proteins from degradation. Nanovaccines are also stable at room temperature, minimizing the need for cold chain storage. Nanoparticle platforms can be synthesized for targeted delivery through intranasal, aerosol, or oral administration to induce desired mucosal immunity. In recent years, several nanovaccine platforms have emerged, based on biodegradable and biocompatible polymers, liposomes, and virus-like particles. While most nanovaccine candidates have not yet advanced beyond testing in rodent models, a growing number have shown promise for use against cattle infectious diseases. This review will highlight recent advancements in polymeric nanovaccine development and the mechanisms by which nanovaccines may interact with the bovine immune system. We will also discuss the positive implications of nanovaccines use for combating several important viral and bacterial disease syndromes and consider important future directions for nanovaccine development in beef and dairy cattle.

Bovine IgG Prevents Experimental Infection With RSV and Facilitates Human T Cell Responses to RSV

Respiratory syncytial virus (RSV) infections represent a major burden of disease in infants and are the second most prevalent cause of death worldwide. Human milk immunoglobulins provide protection against RSV. However, many infants depend on processed bovine milk-based nutrition, which lacks intact immunoglobulins. We investigated the potential of bovine antibodies to neutralize human RSV and facilitate-cell immune activation. We show cow's milk IgG (bIgG) and Intravenous Immunoglobulin (IVIG) have a similar RSV neutralization capacity, even though bIgG has a lower pre-F to post-F binding ratio compared to human IVIG, with the majority of bIgG binding to pre-F. RSV is better neutralized with human IVIG. Consequently, we enriched RSV specific T cells by culturing human PBMC with a mixture of RSV peptides, and used these T cells to study the effect of bIgG and IVIG on the activation of pre-F-pecific T cells. bIgG facilitated in vitro T cell activation in a similar manner as IVIG. Moreover, bIgG was able to mediate T cell activation and internalization of pathogens, which are prerequisites for inducing an adaptive viral response. Using in vivo mouse experiments, we showed that bIgG is able to bind the murine activating IgG Fc Receptors (FcγR), but not the inhibiting FcγRII. Intranasal administration of the monoclonal antibody palivizumab, but also of bIgG and IVIG prevented RSV infection in mice. The concentration of bIgG needed to prevent infection was ~5-fold higher compared to IVIG. In conclusion, the data presented here indicate that functionally active bIgG facilitates adaptive antiviral T cell responses and prevents RSV infection in vitro and in vivo.

Bovine Respiratory Disease Vaccination Against Viral Pathogens: Modified-Live Versus Inactivated Antigen Vaccines, Intranasal Versus Parenteral, What Is the Evidence?

Vaccination of cattle against viral respiratory pathogens to minimize losses associated with bovine respiratory disease (BRD) is a common practice among producers and veterinarians. Three different calf populations in which BRD is most prevalent (recently weaned beef calves, preweaning beef calves, and young dairy calves) are the principal focus of morbidity and mortality prevention through vaccination; however, the evidence of vaccination efficacy is inconsistent in the literature. This review addresses the evidence of efficacy of vaccination in the prevention or reduction of naturally occurring and experimentally induced BRD in each calf group.

Current Animal Models for Understanding the Pathology Caused by the Respiratory Syncytial Virus

The human respiratory syncytial virus (hRSV) is the main etiologic agent of severe lower respiratory tract infections that affect young children throughout the world, associated with significant morbidity and mortality, becoming a serious public health problem globally. Up to date, no licensed vaccines are available to prevent severe hRSV-induced disease, and the generation of safe-effective vaccines has been a challenging task, requiring constant biomedical research aimed to overcome this ailment. Among the difficulties presented by the study of this pathogen, it arises the fact that there is no single animal model that resembles all aspects of the human pathology, which is due to the specificity that this pathogen has for the human host. Thus, for the study of hRSV, different animal models might be employed, depending on the goal of the study. Of all the existing models, the murine model has been the most frequent model of choice for biomedical studies worldwide and has been of great importance at contributing to the development and understanding of vaccines and therapies against hRSV. The most notable use of the murine model is that it is very useful as a first approach in the development of vaccines or therapies such as monoclonal antibodies, suggesting in this way the direction that research could have in other preclinical models that have higher maintenance costs and more complex requirements in its management. However, several additional different models for studying hRSV, such as other rodents, mustelids, ruminants, and non-human primates, have been explored, offering advantages over the murine model. In this review, we discuss the various applications of animal models to the study of hRSV-induced disease and the advantages and disadvantages of each model, highlighting the potential of each model to elucidate different features of the pathology caused by the hRSV infection.

Utility of the Neonatal Calf Model for Testing Vaccines and Intervention Strategies for Use against Human RSV Infection

Respiratory syncytial virus (RSV) is a significant cause of pediatric respiratory tract infections. It is estimated that two-thirds of infants are infected with RSV during the first year of life and it is one of the leading causes of death in this age group worldwide. Similarly, bovine RSV is a primary viral pathogen in cases of pneumonia in young calves and plays a significant role in bovine respiratory disease complex. Importantly, naturally occurring infection of calves with bovine RSV shares many features in common with human RSV infection. Herein, we update our current understanding of RSV infection in cattle, with particular focus on similarities between the calf and human infection, and the recent reports in which the neonatal calf has been employed for the development and testing of vaccines and therapeutics which may be applied to hRSV infection in humans.

Animal models of respiratory syncytial virus infection

Human respiratory syncytial virus (hRSV) is a major cause of respiratory disease and hospitalisation of infants, worldwide, and is also responsible for significant morbidity in adults and excess deaths in the elderly. There is no licensed hRSV vaccine or effective therapeutic agent. However, there are a growing number of hRSV vaccine candidates that have been developed targeting different populations at risk of hRSV infection. Animal models of hRSV play an important role in the preclinical testing of hRSV vaccine candidates and although many have shown efficacy in preclinical studies, few have progressed to clinical trials or they have had only limited success. This is, at least in part, due to the lack of animal models that fully recapitulate the pathogenesis of hRSV infection in humans. This review summarises the strengths and limitations of animal models of hRSV, which include those in which hRSV is used to infect non-human mammalian hosts, and those in which non-human pneumoviruses, such as bovine (b)RSV and pneumonia virus of mice (PVM) are studied in their natural host. Apart from chimpanzees, other non-human primates (NHP) are only semi-permissive for hRSV replication and experimental infection with large doses of virus result in little or no clinical signs of disease, and generally only mild pulmonary pathology. Other animal models such as cotton rats, mice, ferrets, guinea pigs, hamsters, chinchillas, and neonatal lambs are also only semi-permissive for hRSV. Nevertheless, mice and cotton rats have been of value in the development of monoclonal antibody prophylaxis for infants at high risk of severe hRSV infection and have provided insights into mechanisms of immunity to and pathogenesis of hRSV. However, the extent to which they predict hRSV vaccine efficacy and safety is unclear and several hRSV vaccine candidates that are completely protective in rodent models are poorly effective in chimpanzees and other NHP, such as African Green monkeys. Furthermore, interpretation of findings from many rodent and NHP models of vaccine-enhanced hRSV disease has been confounded by sensitisation to non-viral antigens present in the vaccine and challenge virus. Studies of non-human pneumoviruses in their native hosts are more likely to reflect the pathogenesis of natural hRSV infection, and experimental infection of calves with bRSV and of mice with PVM result in clinical disease and extensive pulmonary pathology. These animal models have not only been of value in studies on mechanisms of immunity to and the pathogenesis of pneumovirus infections but have also been used to evaluate hRSV vaccine concepts. Furthermore, the similarities between the epidemiology of bRSV in calves and hRSV in infants and the high level of genetic and antigenic similarity between bRSV and hRSV, make the calf model of bRSV infection a relevant model for preclinical evaluation of hRSV vaccine candidates which contain proteins that are conserved between hRSV and bRSV.

Systematic review and meta-analysis of the effectiveness of commercially available vaccines against bovine herpesvirus, bovine viral diarrhea virus, bovine respiratory syncytial virus, and parainfluenza type 3 virus for mitigation of bovine respiratory disease complex in cattle

OBJECTIVE

To evaluate and analyze data from controlled studies on the effectiveness of vaccinating cattle with commercially available viral antigen vaccines for mitigation of the effects of bovine respiratory disease complex (BRDC).

DESIGN

Systematic review and meta-analysis.

SAMPLE

31 studies comprising 88 trials.

PROCEDURES

Studies that reported the effectiveness of commercially available bovine herpesvirus-1 (BHV-1), bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV), and parainfluenza type 3 virus (PI3) vaccines for protection of cattle against BRDC or its components were included in the analysis. Studies or trials were categorized as natural exposure or experimental challenge and were further divided by the viral antigen evaluated and vaccine type (modified-live virus [MLV] or inactivated vaccine). Meta-analysis was performed; summary Mantel-Haenszel risk ratios were determined, and Forest plots were generated.

RESULTS

In natural exposure trials, beef calves vaccinated with various antigen combinations had a significantly lower BRDC morbidity risk than did nonvaccinated control calves. In trials evaluating BHV-1 and MLV BVDV vaccines in experimental challenge models, vaccinated calves had a lower BRDC morbidity risk than did control calves; however, in experimental challenge trials evaluating MLV BRSV and PI3 vaccines, no significant difference in morbidity or mortality risk was found between vaccinated and control calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Estimating clinical efficacy from results of experimental challenge studies requires caution because these models differ substantially from those involving natural exposure. The literature provides data but does not provide sufficiently strong evidence to guide definitive recommendations for determining which virus components are necessary to include in a vaccination program for prevention or mitigation of BRDC in cattle.

Brief History and Characterization of Enhanced Respiratory Syncytial Virus Disease

In 1967, infants and toddlers immunized with a formalin-inactivated vaccine against respiratory syncytial virus (RSV) experienced an enhanced form of RSV disease characterized by high fever, bronchopneumonia, and wheezing when they became infected with wild-type virus in the community. Hospitalizations were frequent, and two immunized toddlers died upon infection with wild-type RSV. The enhanced disease was initially characterized as a "peribronchiolar monocytic infiltration with some excess in eosinophils." Decades of research defined enhanced RSV disease (ERD) as the result of immunization with antigens not processed in the cytoplasm, resulting in a nonprotective antibody response and CD4(+) T helper priming in the absence of cytotoxic T lymphocytes. This response to vaccination led to a pathogenic Th2 memory response with eosinophil and immune complex deposition in the lungs after RSV infection. In recent years, the field of RSV experienced significant changes. Numerous vaccine candidates with novel designs and formulations are approaching clinical trials, defying our previous understanding of favorable parameters for ERD. This review provides a succinct analysis of these parameters and explores criteria for assessing the risk of ERD in new vaccine candidates.

Immunology of bovine respiratory syncytial virus in calves

Bovine respiratory syncytial virus (BRSV) is an important cause of respiratory disease in young calves. The virus is genetically and antigenically closely related to human (H)RSV, which is a major cause of respiratory disease in young infants. As a natural pathogen of calves, BRSV infection recapitulates the pathogenesis of respiratory disease in man more faithfully than semi-permissive, animal models of HRSV infection. With the increasing availability of immunological reagents, the calf can be used to dissect the pathogenesis of and mechanisms of immunity to RSV infection, to analyse the ways in which the virus proteins interact with components of the innate response, and to evaluate RSV vaccine strategies. Passively transferred, neutralising bovine monoclonal antibodies, which recognise the same epitopes in the HRSV and BRSV fusion (F) protein, can protect calves against BRSV infection, and depletion of different T cells subsets in calves has highlighted the importance of CD8(+) T cells in viral clearance. Calves can be used to model maternal-antibody mediated suppression of RSV vaccine efficacy, and to increase understanding of the mechanisms responsible for RSV vaccine-enhanced respiratory disease.

Duration of immunity to experimental infection with bovine respiratory syncytial virus following intranasal vaccination of young passively immune calves

OBJECTIVE

To determine whether a combination modified-live bovine respiratory syncytial virus (BRSV) vaccine could stimulate protective immunity in young BRSV-seropositive calves following intranasal administration and determine the duration of clinical immunity.

DESIGN

Controlled challenge study. Animals-84 dairy calves (3 to 11 days old).

PROCEDURES

Responses to BRSV challenge of seronegative calves vaccinated under licensing trial conditions were compared with those of seropositive calves 2 times after vaccination. In experiment 1, young BRSV-seronegative calves were vaccinated intranasally with a minimum immunizing dose of BRSV and challenged with BRSV approximately 7 weeks later. In experiments 2 and 3, young BRSV-seropositive calves were vaccinated intranasally with a commercially available combination modified-live virus vaccine containing the commercial dose of the BRSV fraction and challenged with BRSV 9 weeks or approximately 14 weeks later, respectively.

RESULTS

In experiments 1 and 2, BRSV-vaccinated calves had significantly higher Pao2, significantly fewer lung lesions, and significantly lower mortality rate than did unvaccinated calves subsequent to BRSV challenge. In contrast, in experiment 3, there were no differences in Pao2, lung lesions, or mortality rate between vaccinated and control calves after BRSV challenge approximately 14 weeks after vaccination. Protected calves in experiment 1 consistently had significant anamnestic mucosal and systemic antibody responses after challenge, whereas in experiments 2 and 3, antibody responses after challenge were more variable.

CONCLUSIONS AND CLINICAL RELEVANCE

A combination BRSV vaccine administered intranasally to young calves induced protective immunity in the presence of maternal antibodies. The duration of immune responses induced by intranasal vaccination was short (≤ 4 months). Boosting immunity iatrogenically, or by natural exposure, is probably required to obtain optimal responses to neonatal intranasal vaccination.

Bovine model of respiratory syncytial virus infection

Bovine respiratory syncytial virus (BRSV), which is an important cause of respiratory disease in young calves, is genetically and antigenically closely related to human (H)RSV. The epidemiology and pathogenesis of infection with these viruses are similar. The viruses are host-specific and infection produces a spectrum of disease ranging from subclinical to severe bronchiolitis and pneumonia, with the peak incidence of severe disease in individuals less than 6 months of age. BRSV infection in calves reproduces many of the clinical signs associated with HRSV in infants, including fever, rhinorrhoea, coughing, harsh breath sounds and rapid breathing. Although BRSV vaccines have been commercially available for decades, there is a need for greater efficacy. The development of effective BRSV and HRSV vaccines face similar challenges, such as the need to vaccinate at an early age in the presence of maternal antibodies, the failure of natural infection to prevent reinfection, and a history of vaccine-augmented disease. Neutralising monoclonal antibodies (mAbs) to the fusion (F) protein of HRSV, which can protect infants from severe HRSV disease, recognise the F protein of BRSV, and vice versa. Furthermore, bovine and human CD8(+) T-cells, which are known to be important in recovery from RSV infection, recognise similar proteins that are conserved between HRSV and BRSV. Therefore, not only can the bovine model of RSV be used to evaluate vaccine concepts, it can also be used as part of the preclinical assessment of certain HRSV candidate vaccines.

Respiratory syncytial virus infection in cattle

Bovine respiratory syncytial virus (RSV) is a cause of respiratory disease in cattle worldwide. It has an integral role in enzootic pneumonia in young dairy calves and summer pneumonia in nursing beef calves. Furthermore, bovine RSV infection can predispose calves to secondary bacterial infection by organisms such as Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni, resulting in bovine respiratory disease complex, the most prevalent cause of morbidity and mortality among feedlot cattle. Even in cases where animals do not succumb to bovine respiratory disease complex, there can be long-term losses in production performance. This includes reductions in feed efficiency and rate of gain in the feedlot, as well as reproductive performance, milk production, and longevity in the breeding herd. As a result, economic costs to the cattle industry from bovine respiratory disease have been estimated to approach $1 billion annually due to death losses, reduced performance, and costs of vaccinations and treatment modalities. Human and bovine RSV are closely related viruses with similarities in histopathologic lesions and mechanisms of immune modulation induced following infection. Therefore, where appropriate, we provide comparisons between RSV infections in humans and cattle. This review article discusses key aspects of RSV infection of cattle, including epidemiology and strain variability, clinical signs and diagnosis, experimental infection, gross and microscopic lesions, innate and adaptive immune responses, and vaccination strategies.

The path to an RSV vaccine

Respiratory syncytial virus (RSV) is the greatest remaining unmet infant vaccine need in developed countries and an important unmet infant vaccine need worldwide. More than 40 years of effort have yet to result in a licensed RSV vaccine for humans. Key challenges to RSV vaccine development include a peak of severe disease at 2-3 months of age, problematic biochemical behavior of key vaccine antigens, a history of vaccine-mediated disease enhancement, and reliance on animal models that may not accurately reflect human disease processes. Potential paths to overcome these challenges include maternal immunization, structure-based engineering of vaccine antigens, the design of a novel platform for safe infant immunization, and the development of improved animal models for vaccine-enhanced disease.

Neonatal calf infection with respiratory syncytial virus: drawing parallels to the disease in human infants

Respiratory syncytial virus (RSV) is the most common viral cause of childhood acute lower respiratory tract infections. It is estimated that RSV infections result in more than 100,000 deaths annually worldwide. Bovine RSV is a cause of enzootic pneumonia in young dairy calves and summer pneumonia in nursing beef calves. Furthermore, bovine RSV plays a significant role in bovine respiratory disease complex, the most prevalent cause of morbidity and mortality among feedlot cattle. Infection of calves with bovine RSV shares features in common with RSV infection in children, such as an age-dependent susceptibility. In addition, comparable microscopic lesions consisting of bronchiolar neutrophilic infiltrates, epithelial cell necrosis, and syncytial cell formation are observed. Further, our studies have shown an upregulation of pro-inflammatory mediators in RSV-infected calves, including IL-12p40 and CXCL8 (IL-8). This finding is consistent with increased levels of IL-8 observed in children with RSV bronchiolitis. Since rodents lack IL-8, neonatal calves can be useful for studies of IL-8 regulation in response to RSV infection. We have recently found that vitamin D in milk replacer diets can be manipulated to produce calves differing in circulating 25-hydroxyvitamin D3. The results to date indicate that although the vitamin D intracrine pathway is activated during RSV infection, pro-inflammatory mediators frequently inhibited by the vitamin D intacrine pathway in vitro are, in fact, upregulated or unaffected in lungs of infected calves. This review will summarize available data that provide parallels between bovine RSV infection in neonatal calves and human RSV in infants.

Response to experimentally induced infection with bovine respiratory syncytial virus following intranasal vaccination of seropositive and seronegative calves

OBJECTIVE

To determine whether a combination modified-live bovine respiratory syncytial virus (BRSV) vaccine can stimulate protective immunity in young BRSV-seropositive calves following intranasal (IN) administration.

DESIGN

Controlled challenge study.

ANIMALS

66 Holstein bull calves, 3 to 8 days old.

PROCEDURES

In experiment 1, BRSV-seropositive and -seronegative calves were vaccinated IN with a commercially available combination modified-live virus vaccine formulated for SC administration; calves underwent BRSV challenge 4.5 months later. In experiment 2, BRSV-seronegative calves were vaccinated IN or SC (to examine the effect of route of administration) with the same combination vaccine that instead had a 1/100 dose of BRSV (to examine the effect of dose); calves underwent BRSV challenge 21 days later.

RESULTS

In experiment 1, BRSV challenge resulted in severe respiratory tract disease with low arterial partial pressures of oxygen and lung lesions in most calves from all groups. Maximum change in rectal temperature was significantly greater in seropositive IN vaccinated calves, compared with seronegative IN vaccinated and seropositive control calves. Number of days of BRSV shedding was significantly lower in seronegative IN vaccinated calves than in seropositive IN vaccinated and seropositive control calves. In experiment 2, maximum change in rectal temperature was significantly greater in seronegative control calves, compared with seronegative IN and SC vaccinated calves. Shedding of BRSV was significantly reduced in seronegative IN and SC vaccinated calves, compared with control calves; also, lung lesions were reduced in seronegative IN and SC vaccinated calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Maternal antibodies may inhibit priming of protective responses by IN delivered BRSV vaccines.

Immunogenicity of a modified-live virus vaccine against bovine viral diarrhea virus types 1 and 2, infectious bovine rhinotracheitis virus, bovine parainfluenza-3 virus, and bovine respiratory syncytial virus when administered intranasally in young calves

The immunogenicity of an intranasally-administered modified-live virus (MLV) vaccine in 3-8 day old calves was evaluated against bovine viral diarrhea virus (BVDV) types 1 and 2, infectious bovine rhinotracheitis (IBR) virus, parainfluenza-3 (PI-3) virus and bovine respiratory syncytial virus (BRSV). Calves were intranasally vaccinated with a single dose of a multivalent MLV vaccine and were challenged with one of the respective viruses three to four weeks post-vaccination in five separate studies. There was significant sparing of diseases in calves intranasally vaccinated with the MLV vaccine, as indicated by significantly fewer clinical signs, lower rectal temperatures, reduced viral shedding, greater white blood cell and platelet counts, and less severe pulmonary lesions than control animals. This was the first MLV combination vaccine to demonstrate efficacy against BVDV types 1 and 2, IBR, PI-3 and BRSV in calves 3-8 days of age.

Intranasal immunization of mice with a bovine respiratory syncytial virus vaccine induces superior immunity and protection compared to those by subcutaneous delivery or combinations of intranasal and subcutaneous prime-boost strategies

Bovine respiratory syncytial virus (BRSV) infects cells of the respiratory mucosa, so it is desirable to develop a vaccination strategy that induces mucosal immunity. To achieve this, various delivery routes were compared for formalin-inactivated (FI) BRSV formulated with CpG oligodeoxynucleotide (ODN) and polyphosphazene (PP). Intranasal delivery of the FI-BRSV formulation was superior to subcutaneous delivery in terms of antibody, cell-mediated, and mucosal immune responses, as well as reduction in virus replication after BRSV challenge. Although intranasal delivery of FI-BRSV also induced higher serum and lung antibody titers and gamma interferon (IFN-gamma) production in the lungs than intranasal-subcutaneous and/or subcutaneous-intranasal prime-boost strategies, no significant differences were observed in cell-mediated immune responses or virus replication in the lungs of challenged mice. Interleukin 5 (IL-5), eotaxin, and eosinophilia were enhanced after BRSV challenge in the lungs of subcutaneously immunized mice compared to unvaccinated mice, but not in the lungs of mice immunized intranasally or through combinations of the intranasal and subcutaneous routes. These results suggest that two intranasal immunizations with FI-BRSV formulated with CpG ODN and PP are effective and safe as an approach to induce systemic and mucosal responses, as well to reduce virus replication after BRSV challenge. Furthermore, intranasal-subcutaneous and subcutaneous-intranasal prime-boost strategies were also safe and almost as efficacious. In addition to the implications for the development of a protective BRSV vaccine for cattle, formulation with CpG ODN and PP could also prove important in the development of a mucosal vaccine that induces protective immunity against human RSV.

Pulmonary eosinophils and their role in immunopathologic responses to formalin-inactivated pneumonia virus of mice

Enhanced disease is the term used to describe the aberrant Th2-skewed responses to naturally acquired human respiratory syncytial virus (hRSV) infection observed in individuals vaccinated with formalin-inactivated viral Ags. Here we explore this paradigm with pneumonia virus of mice (PVM), a pathogen that faithfully reproduces features of severe hRSV infection in a rodent host. We demonstrate that PVM infection in mice vaccinated with formalin-inactivated Ags from PVM-infected cells (PVM Ags) yields Th2-skewed hypersensitivity, analogous to that observed in response to hRSV. Specifically, we detect elevated levels of IL-4, IL-5, IL-13, and eosinophils in bronchoalveolar lavage fluid of PVM-infected mice that were vaccinated with PVM Ags, but not among mice vaccinated with formalin-inactivated Ags from uninfected cells (control Ags). Interestingly, infection in PVM Ag-vaccinated mice was associated with a approximately 10-fold reduction in lung virus titer and protection against weight loss when compared with infected mice vaccinated with control Ags, despite the absence of serum-neutralizing Abs. Given recent findings documenting a role for eosinophils in promoting clearance of hRSV in vivo, we explored the role of eosinophils in altering the pathogenesis of disease with eosinophil-deficient mice. We found that eosinophil deficiency had no impact on virus titer in PVM Ag-vaccinated mice, nor on weight loss or levels of CCL11 (eotaxin-1), IFN-gamma, IL-5, or IL-13 in bronchoalveolar lavage fluid. However, levels of both IL-4 and CCL3 (macrophage inflammatory protein-1alpha) in bronchoalveolar lavage fluid were markedly diminished in PVM Ag-vaccinated, PVM-infected eosinophil-deficient mice when compared with wild-type controls.

Understanding the mechanisms of viral induced asthma: new therapeutic directions

Asthma is a common and debilitating disease that has substantially increased in prevalence in Western Societies in the last 2 decades. Respiratory tract infections by respiratory syncytial virus (RSV) and rhinovirus (RV) are widely implicated as common causes of the induction and exacerbation of asthma. These infections in early life are associated with the induction of wheeze that may progress to the development of asthma. Infections may also promote airway inflammation and enhance T helper type 2 lymphocyte (Th2 cell) responses that result in exacerbations of established asthma. The mechanisms of how RSV and RV induce and exacerbate asthma are currently being elucidated by clinical studies, in vitro work with human cells and animal models of disease. This research has led to many potential therapeutic strategies and, although none are yet part of clinical practise, they show much promise for the prevention and treatment of viral disease and subsequent asthma.

Human and bovine respiratory syncytial virus vaccine research and development

Human (HRSV) and bovine (BRSV) respiratory syncytial viruses (RSV) are two closely related viruses, which are the most important causative agents of respiratory tract infections of young children and calves, respectively. BRSV vaccines have been available for nearly 2 decades. They probably have reduced the prevalence of RSV infection but their efficacy needs improvement. In contrast, despite decades of research, there is no currently licensed vaccine for the prevention of HRSV disease. Development of a HRSV vaccine for infants has been hindered by the lack of a relevant animal model that develops disease, the need to immunize immunologically immature young infants, the difficulty for live vaccines to find the right balance between attenuation and immunogenicity, and the risk of vaccine-associated disease. During the past 15 years, intensive research into a HRSV vaccine has yielded vaccine candidates, which have been evaluated in animal models and, for some of them, in clinical trials in humans. Recent formulations have focused on subunit vaccines with specific CD4+ Th-1 immune response-activating adjuvants and on genetically engineered live attenuated vaccines. It is likely that different HRSV vaccines and/or combinations of vaccines used sequentially will be needed for the various populations at risk. This review discusses the recent advances in RSV vaccine development.

Immunization strategies for the prevention of pneumovirus infections

Pneumoviruses, which are viruses of the family Paramyxoviridae, subfamily Pneumovirinae, are pathogens that infect the respiratory tract of their host species. The human pneumovirus pathogen, human respiratory syncytial virus (RSV), has counterparts that infect cows (bovine RSV), sheep (ovine RSV), goats (caprine RSV) and rodents (pneumonia virus of mice). Each pneumovirus is host specific and results in a spectrum of disease, ranging from mild upper-respiratory illness to severe bronchiolitis and pneumonia with significant morbidity and mortality. Given the public health burden caused by human RSV and the concomitant agricultural impact of bovine RSV, these two viruses are considered as prime targets for the development of safe and effective vaccines. In this review, we describe the strategies used to develop vaccines against human and bovine RSV and introduce the pneumonia virus mouse model as a novel and invaluable tool for preclinical studies and new vaccine strategies.

Immunopathology of RSV infection: prospects for developing vaccines without this complication

Respiratory syncytial virus is the most important cause of lower respiratory tract infection in infants and young children. RSV clinical disease varies from rhinitis and otitis media to bronchiolitis and pneumonia. An increased incidence of asthma later in life has been associated with the more severe lower respiratory tract infections. Despite its importance as a pathogen, there is no licensed vaccine against RSV. This is due to a number of factors complicating the development of an effective and safe vaccine. The immunity to natural RSV infection is incomplete as re-infections occur in all age groups, which makes it challenging to design a protective vaccine. Second, the primary target population is the newborn infant, which has a relatively immature immune system and maternal antibodies that can interfere with vaccination. Finally, some vaccines have resulted in a predisposition for exacerbated pulmonary disease in infants, which was attributed to an imbalanced Th2-biased immune response, although the exact cause has not been elucidated. This makes it difficult to proceed with vaccine testing in infants. It is likely that an effective and safe vaccine needs to elicit a balanced immune response, including RSV-specific neutralising antibodies, CD8 T-cells, Th1/Th2 CD4 T-cells and preferably secretory IgA. Subunit vaccines formulated with appropriate adjuvants may be adequate for previously exposed individuals. However, intranasally delivered genetically engineered attenuated or vectored vaccines are currently most promising for newborns, as they are expected to induce a balanced immune response similar to that elicited to natural infection and not be subject to interference from maternal antibodies. Maternal vaccination may be the optimal strategy to protect the very young infants.

Response of calves to challenge exposure with virulent bovine respiratory syncytial virus following intranasal administration of vaccines formulated for parenteral administration

OBJECTIVE

To determine whether single-fraction and combination modified-live bovine respiratory syncytial virus (BRSV) vaccines commercially licensed for parenteral administration could stimulate protective immunity in calves after intranasal administration.

DESIGN

Randomized controlled trial.

ANIMALS

39 calves.

PROCEDURES

Calves were separated from dams at birth, fed colostrum with a minimal concentration of antibodies against BRSV, and maintained in isolation. In 2 preliminary experiments, 9-week-old calves received 1 (n = 3) or 2 (3) doses of a single-component, modified-live BRSV vaccine or no vaccine (8 control calves in each experiment), and were challenged with BRSV 21 days after vaccination. In a third experiment, 2-week-old calves received combination modified-live virus (MLV) vaccines with or without BRSV and calves were challenged with BRSV 8 days later. Calves were euthanized, and lung lesions were measured. Immune responses, including serum and nasal antibody and nasal interferon-alpha concentrations, were assessed.

RESULTS

BRSV challenge induced signs of severe clinical respiratory tract disease, including death and pulmonary lesions in unvaccinated calves and in calves that received a combination viral vaccine without BRSV. Pulmonary lesions were significantly less severe in BRSV-challenged calves that received single or combination BRSV vaccines. The proportion of calves that shed virus and the peak virus titer was decreased, compared with control calves. Protection was associated with mucosal IgA antibody responses after challenge.

CONCLUSIONS AND CLINICAL RELEVANCE

Single and combination BRSV vaccines administered intranasally provided clinical protection and sparing of pulmonary tissue similar to that detected in response to parenteral delivery of combination MLV and inactivated BRSV vaccines previously assessed in the same challenge model.

Effects of experimental inoculation of bovine respiratory syncytial virus in different inbred mice lineages: Establishment of a murine model for BRSV infection

Bovine respiratory syncytial virus (BRSV), a member of the subfamily Pneumovirinae, family Paramyxoviridae, is a major cause of respiratory disorders in young cattle. A number of studies were conducted to validate a reliable animal model for the infection, since BRSV inoculation on the natural host is costly and often unsuccessful. Unfortunately, after inoculation of BRSV in Balb/C mice, viral replication may be detected; however, evident pathological alterations are absent on the experimentally infected animals. In order to establish a mice model that could be used further for preliminary studies of pathological and immunological aspects of BRSV infection, three mice inbred lineages (Balb/C, A/J and C57BL6), possessing different genetic backgrounds, were tested about its susceptibility to the inoculation with BRSV. Animals were inoculated through the nasal and ocular routes and were observed after inoculation. At 7 days post-inoculation (dpi) animals were necropsied and virological (virus isolation and viral nucleic acid amplification) as well as histopathological examinations were performed. A/J and C57BL6 showed interstitial pneumonia, when compared to the Balb/C group. These findings shows that mice may constitute a suitable model for the study of BRSV infections, depending on the mice strain used for experimental inoculations.

Immune responses and disease enhancement during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is one of the commonest and most troublesome viruses of infancy. It causes most cases of bronchiolitis, which is associated with wheezing in later childhood. In primary infection, the peak of disease typically coincides with the development of specific T- and B-cell responses, which seem, in large part, to be responsible for disease. Animal models clearly show that a range of immune responses can enhance disease severity, particularly after vaccination with formalin-inactivated RSV. Prior immune sensitization leads to exuberant chemokine production, an excessive cellular influx, and an overabundance of cytokines during RSV challenge. Under different circumstances, specific mediators and T-cell subsets and antibody-antigen immune complex deposition are incriminated as major factors in disease. Animal models of immune enhancement permit a deep understanding of the role of specific immune responses in RSV disease, assist in vaccine design, and indicate which immunomodulatory therapy might be beneficial to children with bronchiolitis.

Bovine respiratory syncytial virus ISCOMs--protection in the presence of maternal antibodies

The protection induced by immunostimulating complexes (ISCOMs) against bovine respiratory syncytial virus (BRSV) was evaluated and compared to that of a commercial inactivated vaccine (CV) in calves with BRSV-specific maternal antibodies. Following experimental challenge, controls (n = 4) and animals immunized with CV (n = 5) developed moderate to severe respiratory disease, whereas calves immunized with ISCOMs (n = 5) remained clinically healthy. BRSV was re-isolated from the nasopharynx of all controls and from all calves immunized with CV, but from none of the calves immunized with ISCOMs. BRSV-RNA was detected by real-time PCR from a single animal in this group. Significantly higher BRSV-specific nasal IgG, serum IgG1 and IgG2 titers were detected before and after challenge in animals immunized with ISCOMs versus CV. In conclusion, the ISCOMs overcame the suppressive effect of maternal antibodies in calves and induced strong clinical and virological protection against a BRSV challenge.

Evaluation of efficacy of an inactivated vaccine against bovine respiratory syncytial virus in calves with maternal antibodies

OBJECTIVE

To assess short- and long-term efficacy of an inactivated bovine respiratory syncytial virus (BRSV) vaccine administered i.m. to calves with maternally derived antibodies.

ANIMALS

28 two-week-old calves with neutralizing, maternally derived antibodies against BRSV.

PROCEDURE

For evaluation of short-term efficacy, 6 calves were vaccinated i.m. at 2 and 6 weeks of age and challenged intranasally and intratracheally along with a matched group of 4 unvaccinated control calves at 10 weeks of age. For evaluation of long-term efficacy, 2 groups of 6 calves each were vaccinated i.m. at 2, 6, and 18 weeks of age or 14 and 18 weeks of age; these calves were challenged intranasally and intratracheally along with 6 matched unvaccinated control calves at 43 weeks of age. Serum virus neutralizing antibody titer, clinical reactions, and virus shedding in nasal mucus and lung washings were assessed.

RESULTS

None of the vaccination regimens resulted in a significant increase in serum virus neutralizing antibody titer. As judged by virus shedding in nasal mucus and lung washings, vaccinated calves were protected against challenge, compared with unvaccinated control groups. Clinical signs attributable to challenge were coughing (short-term efficacy study) and tachypnea and dyspnea (long-term efficacy study). The severity and incidence of disease were significantly lower in the vaccinated groups, compared with that in the unvaccinated groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Through vaccination, it is possible to protect vulnerable calves with maternal antibodies against BRSV infection and reduce respiratory tract disease.

Animal pneumoviruses: molecular genetics and pathogenesis

Pneumoviruses are single-stranded, negative-sense, nonsegmented RNA viruses of the family Paramyxoviridae, subfamily Pneumovirinae, and include pathogens that infect humans (respiratory syncytial virus and human metapneumovirus), domestic mammals (bovine, ovine, and caprine respiratory syncytial viruses), rodents (pneumonia virus of mice), and birds (avian metapneumovirus). Among the topics considered in this review are recent studies focused on the roles of the individual virus-encoded components in promoting virus replication as well as in altering and evading innate antiviral host defenses. Advances in the molecular technology of pneumoviruses and the emergence of recombinant pneumoviruses that are leading to improved virus-based vaccine formulations are also discussed. Since pneumovirus infection in natural hosts is associated with a profound inflammatory response that persists despite adequate antiviral therapy, we also review the recent experimental treatment strategies that have focused on combined antiviral, anti-inflammatory, and immunomodulatory approaches.

Cytotoxic T lymphocyte activity and cytokine expression in calves vaccinated with formalin-inactivated bovine respiratory syncytial virus prior to challenge

The development of effective, safe vaccines for human and bovine respiratory syncytial virus (RSV) has been problematic. Inactivated RSV vaccines are of variable efficacy; poor efficacy may be related to induction of ineffective cell-mediated immunity (CMI). To characterize CMI in calves vaccinated with formalin inactivated (FI) BRSV, 11 calves were vaccinated twice with FI-BRSV (n=5) or mock vaccine (n=6) at a 2 week interval and challenged 1 month later. Prior to challenge a cannula was placed in the efferent lymphatic of the caudal mediastinal lymph node of each calf; lymph derived lymphocytes (LDL) were collected for analysis of CMI. Cytotoxic T lymphocyte (CTL) activity by LDL and/or peripheral blood mononuclear cells (PBMC) was measured by 51Cr release on days 5, 7, 9, and 10 post-challenge. Messenger RNA for interferon gamma (IFN-gamma), interleukin 2 (IL-2) and IL-4 was measured on days 0-10 by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) of RNA of LDL. BRSV-specific IFN-gamma production by PBMC was measured on days 0 and 10 by ELISA. Clinical signs and postmortem changes following challenge were evaluated. There was no difference between groups in clinical signs, postmortem changes, CTL activity, cytokine message expression, or IFN-gamma production. For both groups, percentage lysis by CTL peaked on days 7-10 and ranged from 11 to 25%. Failure of vaccination to prevent disease following challenge was likely associated with failure to prime for improved CMI responses.

Vaccine-induced immunopathology during bovine respiratory syncytial virus infection: exploring the parameters of pathogenesis

The bovine and human respiratory syncytial viruses cause severe lower respiratory tract infections. Effective vaccines against the respiratory syncytial viruses have been lacking since vaccine failures in the 1960s and 1970s. In this report, we describe a bovine respiratory syncytial virus (bRSV) challenge model in which both classical bRSV respiratory infection and vaccine-enhanced immune pathology were reproduced. The classical, formalin-inactivated (FI) bRSV vaccine that has been associated with vaccine failure was efficient in inducing high antibody titers and reducing viral loads but also primed calves for a far more serious enhanced respiratory disease after a bRSV challenge, thereby mimicking the enhanced clinical situation in FI human RSV (hRSV)-immunized and hRSV-infected infants in the 1960s. We show that immunization with FI-bRSV mainly primes a Th2-like inflammatory response that is characterized by a significant eosinophilic influx in the bronchial alveolar lung fluid and lung tissues and high levels of immunoglobulin E serum antibodies. The current model may be useful in the evaluation of new bRSV candidate vaccines for potency and safety.

Rapid onset of protection following vaccination of calves with multivalent vaccines containing modified-live or modified-live and killed BHV-1 is associated with virus-specific interferon gamma production

The objective of this study was to determine the effect of vaccination with commercially-available multivalent vaccines containing either modified-live (MLV) bovine herpesvirus-1 (BHV-1) (Bovishield) or MLV plus killed (MLV + K) BHV-1 (Reliant Plus) on protection against challenge at 5 days after a single vaccination. An additional objective was to determine whether cell-mediated immunity as measured by virus-specific interferon gamma (IFN-gamma) production by peripheral blood mononuclear cells (PBMC) was associated with any early protection induced by vaccination. Clinical signs, serum neutralizing (SN) titers, and nasal virus isolation (VI) titers were also measured. The 12-16-week-old dairy cross-calves seronegative for antibodies to BHV-1 were vaccinated with a multivalent vaccine containing MLV BHV-1 (n = 19), a multivalent vaccine containing MLV + K BHV-1 (n = 19), or a control multivalent vaccine not containing BHV-1 (n = 10) on day 0 and challenged intranasally on day 5. PBMC were isolated on days 0, 3, 5, 8, 10, 14 and 19. PBMC were incubated in vitro with spent media, live BHV-1, or heat-inactivated BHV-1 for 72 h. Supernatants were assayed for bovine IFN-gamma by ELISA. Bovine herpesvirus-1-specific IFN-gamma production was expressed as percent of the kit positive control, with value for spent media subtracted. Clinical signs were monitored daily. Serum VN titers were measured on days 0-5 and 19. Nasal VI titer was measured every other day from days 5 to 19. Interferon gamma production was higher on day 5, and was significantly increased post-challenge, in both vaccine groups compared to controls. There was no difference between vaccine groups on any day. There was no significant difference in SN titer among groups on any day. Virus isolation titer was significantly higher in controls on days 6 and 8 compared to both vaccine groups. Temperatures were significantly higher and nasal discharge was present more often post-challenge in controls compared to vaccine groups. Vaccination 5 days prior to challenge with commercially-available vaccine containing MLV or MLV + K BHV-1 was associated with increased BHV-1-specific IFN-gamma production, decreased viral shedding, lower temperatures and less nasal discharge post-challenge. Cell mediated immune responses as measured by IFN-gamma production are stimulated rapidly following BHV-1 vaccination of calves.

An experimental infection model for reproduction of calf pneumonia with bovine respiratory syncytial virus (BRSV) based on one combined exposure of calves

Bovine respiratory syncytial virus (BRSV) has been recognised as an important pathogen in calf pneumonia for 30 years, but surprisingly few effective infection models for studies of the immune response and the pathogenesis in the natural host have been established. We present a reproducible experimental infection model for BRSV in 2-5-month-old, conventionally reared Jersey calves. Thirty-four colostrum-fed calves were inoculated once by aerosol and intratracheal injection with BRSV. Respiratory disease was recorded in 91% of the BRSV-inoculated calves, 72% had an accompanying rise in rectal temperature and 83% exhibited >5% consolidation of the lung tissue. The disease closely resembled natural outbreaks of BRSV-related pneumonia, and detection of BRSV in nasal secretions and lung tissues confirmed the primary role of BRSV. Nine mock-inoculated control calves failed to develop respiratory disease. This model is a valuable tool for the study of the pathogenesis of BRSV and for vaccine efficacy studies.

Mucosal immunization with live recombinant bovine respiratory syncytial virus (BRSV) and recombinant BRSV lacking the envelope glycoprotein G protects against challenge with wild-type BRSV

Recombinant bovine respiratory syncytial virus (rBRSV) and an rBRSV deletion mutant lacking the G gene (rBRSVDeltaG) were characterized in calves with respect to replication competence, attenuation, and protective efficacy as live-attenuated BRSV vaccines. Both recombinant viruses were safe and induced protection against a BRSV challenge infection. rBRSV replicated efficiently in the upper respiratory tract. Intranasal immunization with rBRSVDeltaG led to infection but not to mucosal virus replication. Neutralizing antibodies were induced by rBRSV and rBRSVDeltaG. Thus, the BRSV attachment glycoprotein G seems to be dispensable in vaccinating calves against BRSV.

T-cell populations responsive to bovine respiratory syncytial virus in seronegative calves

Calves lacking detectable serum antibodies against bovine respiratory syncytial virus (BRSV) were screened for virus-specific T-cell memory. Peripheral blood mononuclear cells were cultured in vitro with live BRSV and analyzed by dual-color flow cytometry for surface expression of CD25 on CD4(+), CD8(+), and gammadeltaT-cells. Significant recall responses were detected in some of the seronegative calves. Modified live BRSV vaccine was administered to these and to a group of non-responding calves. Following vaccination, virus-specific IgG, virus neutralizing antibody, and T-cell recall responses were all elevated more rapidly in the group with BRSV-sensitive T-cells than in the T-cell-negative group, which suggested that calves in the first group were previously exposed to BRSV. This demonstrates that exposure to BRSV can induce T and B cell memory in young calves without causing seroconversion. The calves were presumably exposed to BRSV while they had maternal antibody, which inhibited the calves from developing an antibody response.

The immunology of the bovine respiratory disease complex

The bovine respiratory disease complex continues to be an economically important syndrome in an era when immunologic control is likely to become increasingly important. Recent studies have yielded a better understanding of the interaction, at the molecular level, of various pathogens with the bovine immune system. Improved challenge models for important viral pathogens such as bovine viral diarrhea virus and bovine respiratory syncytial virus have provided evidence of the efficacy of immune responses stimulated by vaccination. This article highlights recent advances in understanding of the role of the immune response in the pathogenesis and prophylaxis of bovine respiratory disease complex.

Efficacy of an inactivated respiratory syncytial virus vaccine in calves

OBJECTIVE

To determine whether an inactivated bovine respiratory syncytial virus (BRSV) vaccine would protect calves from infection with virulent BRSV.

DESIGN

Randomized controlled trial.

ANIMALS

27 nine-week-old calves seronegative for BRSV exposure.

PROCEDURE

Group-1 calves (n = 9) were not vaccinated. Group-2 calves (n = 9) were vaccinated on days 0 and 21 with an inactivated BRSV vaccine containing a minimum immunizing dose of antigen. Group-3 calves (n = 9) were vaccinated on days 0 and 21 with an inactivated BRSV vaccine containing an amount of antigen similar to that in a commercial vaccine. All calves were challenged with virulent BRSV on day 42. Clinical signs and immune responses were monitored for 8 days after challenge. Calves were euthanatized on day 50, and lungs were examined for lesions.

RESULTS

Vaccination elicited increases in BRSV-specific IgG and virus neutralizing antibody titers and in production of interferon-gamma. Virus neutralizing antibody titers were consistently less than IgG titers. Challenge with BRSV resulted in severe respiratory tract disease and extensive pulmonary lesions in control calves, whereas vaccinated calves had less severe signs of clinical disease and less extensive pulmonary lesions. The percentage of vaccinated calves that shed virus in nasal secretions was significantly lower than the percentage of control calves that did, and peak viral titer was lower for vaccinated than for control calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that the inactivated BRSV vaccine provided clinical protection from experimental infection with virulent virus and decreased the severity of pulmonary lesions. Efficacy was similar to that reported for modified-live BRSV vaccines.

The efficacy of modified-live bovine respiratory syncytial virus vaccines in experimentally infected calves

The efficacy of modified-live (MLV) bovine respiratory syncytial virus (BRSV) vaccines and the correlates of vaccine-induced immunity were investigated in calves using a virulent experimental infection. Clinical disease and pulmonary pathology were significantly reduced, relative to unvaccinated controls, in calves vaccinated according to label directions with commercial multivalent MLV BRSV vaccines. In vitro assays of cellular immunity were more consistent correlates of vaccine associated protection than presence of post vaccination serum antibody. Most vaccinated calves shed virus, but peak virus titre was suppressed compared to unvaccinated controls, with clearance coincident with the simultaneous appearance of mucosal antibody, cytotoxic cells in the lung and anamnestic or primary serum antibody responses. Virus clearance in unvaccinated calves was coincident with the appearance of BRSV specific cytotoxic cells, before mucosal antibody was detected.