Subgrouping of bovine respiratory syncytial virus strains detected in lung tissue

Molecular characterization of G and F protein genes of bovine respiratory syncytial virus detected from dead calves caused by severe respiratory syndrome: emergence of novel mutations and their importance

Bovine respiratory syncytial virus (BRSV) is an important viral agent in bovine respiratory disease complex affecting young calves from asymptomatic to fatal. Although BRSV is widely prevalent in Türkiye as in other parts of the world, there are limited molecular studies on BRSV in Türkiye. Therefore, in order to better understand the characteristics of circulating BRSV in Türkiye, a study based on the molecular analysis of both F and G proteins was performed. For this purpose, the presence of BRSV was investigated in 20 calves that died as a result of severe respiratory syndrome in the western region of Türkiye in 2020. Nested PCR was performed for both gene regions, and the products were sequenced. Four samples detected as BRSV positive were identified as genotype III according to both gene regions in molecular analysis. However, they were separated into two distinct clusters due to significant differences in nucleotide (90.09-99.54%) and amino acid (85.42-99.31%) similarities between them. Besides, two positive samples in the same cluster were even more different from previously detected Turkish isolates (90.78-92.17% nt and 87.50-89.58% aa). More over, we detected nine novel aa mutations in the extracellular domain, an immunologically important region in the G protein of the virus, that have not been reported in other world isolates found in Genbank until now. These findings suggest that there may be many different viruses in circulation that have the ability to escape the immune system. We recommend that these findings be taken into account in planning both vaccine and epidemiological studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-023-00846-7.

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.

Molecular characterization of Brazilian wild-type strains of bovine respiratory syncytial virus reveals genetic diversity and a putative new subgroup of the virus

Background

Bovine orthopneumovirus, formerly known as bovine respiratory syncytial virus (BRSV), is frequently associated with bovine respiratory disease (BRD).

Aim

To perform the molecular characterization of the G and F proteins of Brazilian wild-type BRSV strains derived from bovine respiratory infections in both beef and dairy cattle.

Materials and Methods

Ten BRSV strains derived from a dairy heifer rearing unit (n = 3) in 2011 and steers of three other feedlots (n = 7) in 2014 and 2015 were analyzed. For the BRSV G and F partial gene amplifications, RT-nested-PCR assays were performed with sequencing in both directions with forward and reverse primers used.

Results

The G gene-based analysis revealed that two strains were highly similar to the BRSV sequences representative of subgroup III, including the Bayovac vaccine strain. However, the remaining seven Brazilian BRSV strains were diverse when compared with strains representative of the BRSV I to VIII subgroups. The central hydrophobic region of the Brazilian BRSV G gene showed the replacement of conserved cysteines and other residues of importance to antibody reactivity. The deduced F gene amino acid sequences from the Brazilian BRSV strains showed changes that were absent in the representative sequences of the known subgroups. Viral isolation on the nasopharyngeal swab suspensions failed to isolate BRSV.

Conclusion

Results suggest that these strains represent a putative new subgroup of BRSV with mutations observed in the immunodominant region of the G protein. However, further studies on these Brazilian BRSV strains should be performed to establish their pathogenic potential.

Occurrence and phylogenetic analysis of bovine respiratory syncytial virus in outbreaks of respiratory disease in Norway

Background

Bovine respiratory syncytial virus (BRSV) is one of the major pathogens involved in the bovine respiratory disease (BRD) complex. The seroprevalence to BRSV in Norwegian cattle herds is high, but its role in epidemics of respiratory disease is unclear. The aims of the study were to investigate the etiological role of BRSV and other respiratory viruses in epidemics of BRD and to perform phylogenetic analysis of Norwegian BRSV strains.

Results

BRSV infection was detected either serologically and/or virologically in 18 (86%) of 21 outbreaks and in most cases as a single viral agent. When serology indicated that bovine coronavirus and/or bovine parainfluenza virus 3 were present, the number of BRSV positive animals in the herd was always higher, supporting the view of BRSV as the main pathogen. Sequencing of the G gene of BRSV positive samples showed that the current circulating Norwegian BRSVs belong to genetic subgroup II, along with other North European isolates. One isolate from an outbreak in Norway in 1976 was also investigated. This strain formed a separate branch in subgroup II, clearly different from the current Scandinavian sequences. The currently circulating BRSV could be divided into two different strains that were present in the same geographical area at the same time. The sequence variations between the two strains were in an antigenic important part of the G protein.

Conclusion

The results demonstrated that BRSV is the most important etiological agent of epidemics of BRD in Norway and that it often acts as the only viral agent. The phylogenetic analysis of the Norwegian strains of BRSV and several previously published isolates supported the theory of geographical and temporal clustering of BRSV.

Immunogenetic responses in calves to intranasal delivery of bovine respiratory syncytial virus (BRSV) epitopes encapsulated in poly (DL-lactide-co-glycolide) microparticles

Bovine respiratory syncytial virus (BRSV) is the principal aetiological agent of the bovine respiratory disease complex. A BRSV subunit vaccine candidate consisting of two synthetic peptides representing putative protective epitopes on BRSV surface glycoproteins in soluble form or encapsulated in poly(lactide-co-glycolide) (PLG) microparticles were prepared. Calves (10 weeks old) with diminishing levels of BRSV-specific maternal antibody were intranasally administered a single dose of the different peptide formulations. Peptide-specific local immune responses (nasal secretion IgA), but not systemic humoral (serum IgG) or cellular responses (serum IFN-γ), were generated by all forms of peptide. There was a significant reduction in occurrence of respiratory disease in the animals inoculated with all peptide formulations compared to animals given PBS alone. Furthermore no adverse effects were observed in any of the animals post vaccination. These results suggest that intranasal immunisation with the peptide subunit vaccine does induce an as yet unidentified protective immune response.

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.

In vivo evidence for quasispecies distributions in the bovine respiratory syncytial virus genome

We analysed the genetic evolution of bovine respiratory syncytial virus (BRSV) isolate W2-00131, from its isolation in bovine turbinate (BT) cells to its inoculation in calves. Results showed that the BRSV genomic region encoding the highly variable glycoprotein G remained genetically stable after virus isolation and over 10 serial infections in BT cells, as well as following experimental inoculation in calves. This remarkable genetic stability led us to examine the mutant spectrum of several populations derived from this field isolate. Sequence analysis of molecular clones revealed an important genetic heterogeneity in the G-coding region of each population, with mutation frequencies ranging from 6.8 to 10.1×10−4substitutions per nucleotide. The non-synonymous mutations of the mutant spectrum mapped preferentially within the two variable antigenic regions of the ectodomain or close to the highly conserved domain. These results suggest that BRSV populations may evolve as complex and dynamic mutant swarms, despite apparent genetic stability.

Bovine respiratory syncytial virus infection

Bovine respiratory syncytial virus (BRSV) belongs to the pneumovirus genus within the family Paramyxoviridae and is a major cause of respiratory disease in young calves. BRSV is enveloped and contains a negative sense, single-stranded RNA genome encoding 11 proteins. The virus replicates predominantly in ciliated respiratory epithelial cells but also in type II pneumocytes. It appears to cause little or no cytopathology in ciliated epithelial cell cultures in vitro, suggesting that much of the pathology is due to the host's response to virus infection. RSV infection induces an array of pro-inflammatory chemokines and cytokines that recruit neutrophils, macrophages and lymphocytes to the respiratory tract resulting in respiratory disease. Although the mechanisms responsible for induction of these chemokines and cytokines are unclear, studies on the closely related human (H)RSV suggest that activation of NF-kappaB via TLR4 and TLR3 signalling pathways is involved. An understanding of the mechanisms by which BRSV is able to establish infection and induce an inflammatory response has been facilitated by advances in reverse genetics, which have enabled manipulation of the virus genome. These studies have demonstrated an important role for the non-structural proteins in anti-interferon activity, a role for a virokinin, released during proteolytic cleavage of the fusion protein, in the inflammatory response and a role for the SH and the secreted form of the G protein in establishing pulmonary infection. Knowledge gained from these studies has also provided the opportunity to develop safe, stable, live attenuated virus vaccine candidates.

Phylogenetic relationships of Brazilian bovine respiratory syncytial virus isolates and molecular homology modeling of attachment glycoprotein

Bovine respiratory syncytial virus (BRSV) causes lower respiratory tract disease in young cattle. Recently, it was possible to determine the sequence of the G protein gene, which plays a role in the attachment of BRSV particles to the cells, from three distinct Brazilian isolates. The phylogenetic analysis conducted here using those sequences compared to other worldwide distributed isolates of BRSV allow us to allocate Brazilian strains within the subgroup B, which was no longer found in the world since the 1970s. One of the Brazilian strains has a major mutation between amino acid residues 173 and 178, within the central hydrophobic conserved region, exactly on the site of two of the four cysteine-noose forming cysteine residues. Homology modeling with the previously determined NMR structure of this protein domain was made to check whether these mutations altered the three-dimensional conformation of this immunodominant region. Possible consequences on the biological effects induced by such mutation on the G protein are discussed.

Real Time RT-PCR for the detection and quantitation of bovine respiratory syncytial virus

A quantitative Real Time RT-PCR assay was developed to detect and quantify bovine respiratory syncytial virus (BRSV) in the respiratory tract of infected animals. A pair of primers and a TaqMan probe targeting conserved regions of the nucleoprotein gene of BRSV were designed. The detection limit of the assay was shown to be 10(3) RNA copies and standard curve demonstrated a linear range from 10(3) to 10(8) copies as well as an excellent reproducibility. The efficiency of the BRSV Real Time RT-PCR was then assessed by detecting BRSV in lungs, tracheas and bronchoalveaolar fluids (BAL) samples of experimentally infected calves. The assay was shown to be 100 times more sensitive than conventional RT-PCR and was more efficient for BRSV diagnosis. Finally, the Real Time RT-PCR was used to quantify BRSV load in BAL fluids of four experimentally infected calves for 14 days. The high sensitivity, rapidity and reproducibility of the BRSV Real Time RT-PCR make this method suitable for diagnostic and for the evaluation of the efficiency of new vaccines.

Restriction enzyme analysis of RT-PCR amplicons as a rapid method for detection of genetic diversity among bovine respiratory syncytial virus isolates

Our current knowledge of antigenic variability of the bovine respiratory syncytial virus (BRSV) is quite limited and is mainly dependent on the use of monoclonal antibodies (mAb). In this study, we present not only analysis of the antigenic, but also of the genetic variability of BRSV. Using a panel of BRSV-specific mAb we distinguished five main reactivity patterns, three of which corresponded to the previously established subgroups A, B and AB. A single viral strain yielded the fourth pattern, while four viral strains did not react with any of the used mAbs forming the fifth pattern. To investigate the genetic basis for the antigenic heterogeneity of the BRS virus G protein, DNA of 11 BRSV isolates was directly sequenced. The comparison of the obtained nucleotide or amino acid sequences to those BRSV strains present in the GenBank revealed 88.1-99.4% and 77.7-98.4% similarity, respectively. These results supported the previously stated suggestion to type BRSV isolates according to their genetic relationship. In order to introduce a rapid and simple method to study the genetic variability of BRSV, we utilized the restriction enzyme analysis of RT-PCR products derived from mRNAs corresponding to the most variable region of the BRSV glycoprotein G ectodomain. Using this restriction enzyme analysis we were able to identify genetic variability among BRSV isolates. The detected non-synonymous mutations led frequently to a change in digestion pattern and were predominantly located in two mucin-like regions of the G protein gene. A correlation has been found between grouping of isolates in the phylogenetic tree and their restriction patterns clustering together isolates with the same restriction profiles. However, viruses placed distant in the tree sharing the same restriction patterns were detected supposing that phylogenetic analysis should be necessary for BRSV typing. Thus, we propose to use DNA restriction polymorphism for a rapid detection of genetic variants among BRSV isolates circulating in cattle population and as a preliminary tool for their typing.

Genetic and Antigenic Analyses of Bovine Respiratory Syncytial Virus Detected in Japan

Genetic and antigenic analyses of bovine respiratory syncytial virus were conducted on 12 field strains from Tohoku and Hokuriku districts in Japan during from 2002 to 2004. On the phylogenetic tree of the nucleotide sequences of the glycoprotein region, the examined strains fell in the same cluster as the strain isolated in Nebraska and were classified as the subgroup III. The examined strains were subdivided into 2 lineages (A, B). Isoleucine 200 of the epitope domain was replaced by threonine as a feature of the lineage B strains. The examined strains showed the nucleotide sequence homologies of 88.3-93.3% with the known Japanese strains classified as the subgroup II and of 86.1-96.6% with those in the subgroup III. No significant difference was found on the neutralization index between the examined strain and the 52-163-13 phylogenetically similar to the Japanese vaccine one. The results suggest that the subgroup III strains have existed in Japan and that epidemics of the strains could be protected due to the present vaccination.

Recent isolates of bovine respiratory syncytial virus from Britain are more closely related to isolates from USA than to earlier British and current mainland European isolates

Eight isolates of Bovine respiratory syncytial virus (BRSV) were made from calves with severe respiratory disease on seven farms in one region of Britain. Genetic analysis of the viruses showed that seven, which were isolated between 1997 and 1999 were almost identical and were distinguishable from an earlier 1991 isolate. When compared with the available sequences of BRSVs from other countries, the recent British isolates were more closely related to US isolates than to earlier British and current mainland European isolates.

Evolution of bovine respiratory syncytial virus

Until now, the analysis of the genetic diversity of bovine respiratory syncytial virus (BRSV) has been based on small numbers of field isolates. In this report, we determined the nucleotide and deduced amino acid sequences of regions of the nucleoprotein (N protein), fusion protein (F protein), and glycoprotein (G protein) of 54 European and North American isolates and compared them with the sequences of 33 isolates of BRSV obtained from the databases, together with those of 2 human respiratory syncytial viruses and 1 ovine respiratory syncytial virus. A clustering of BRSV sequences according to geographical origin was observed. We also set out to show that a continuous evolution of the sequences of the N, G, and F proteins of BRSV has been occurring in isolates since 1967 in countries where vaccination was widely used. The exertion of a strong positive selective pressure on the mucin-like region of the G protein and on particular sites of the N and F proteins is also demonstrated. Furthermore, mutations which are located in the conserved central hydrophobic part of the ectodomain of the G protein and which result in the loss of four Cys residues and in the suppression of two disulfide bridges and an alpha helix critical to the three-dimensional structure of the G protein have been detected in some recent French BRSV isolates. This conserved central region, which is immunodominant in BRSV G protein, thus has been modified in recent isolates. This work demonstrates that the evolution of BRSV should be taken into account in the rational development of future vaccines.

Bovine respiratory syncytial virus (BRSV): a review

Bovine respiratory syncytial virus (BRSV) infection is the major cause of respiratory disease in calves during the first year of life. The study of the virus has been difficult because of its lability and very poor growth in cell culture. However, during the last decade, the introduction of new immunological and biotechnological techniques has facilitated a more extensive study of BRSV as illustrated by the increasing number of papers published. Despite this growing focus, many aspects of the pathogenesis, epidemiology, immunology etc. remain obscure. The course and outcome of the infection is very complex and unpredictable which makes the diagnosis and subsequent therapy very difficult. BRSV is closely related to human respiratory syncytial virus (HRSV) which is an important cause of respiratory disease in young children. In contrast to BRSV, the recent knowledge of HRSV is regularly extensively reviewed in several books and journals. The present paper contains an updated review on BRSV covering most aspects of the structure, molecular biology, pathogenesis, pathology, clinical features, epidemiology, diagnosis and immunology based on approximately 140 references from international research journals.

A bovine respiratory syncytial virus strain with mutations in subgroup-specific antigenic domains of the G protein induces partial heterologous protection in cattle

Bovine respiratory syncytial virus (BRSV) strains are tentatively divided in subgroups A, AB and B, based on antigenic differences of the G protein. A Dutch BRSV strain (Waiboerhoeve: WBH), could not be assigned to one of the subgroups, because the strain did not react with any monoclonal antibody against the G protein. We describe here that the WBH strain has accumulated critical mutations in subgroup-specific domains of the G protein gene, which also occur but then independently in G protein genes of BRSV subgroup A or B strains. Although the comparison of nucleotide residues 256-792 of the G gene of the WBH strain with those of subgroup A and B strains showed that the G gene of the WBH strain is different from that of BRSV subgroup A and B strains, the sequence divergence was not more than observed within the G genes of human respiratory syncytial virus subgroup A or B strains. The WBH strain did not induce severe disease after experimental infection of calves, and induced partial protection against a heterologous challenge. Despite the dissimilarity of the conserved central regions of the G protein of the WBH strain and that of the challenge strain, a secondary antibody response against this region was induced in WBH-infected calves after challenge. We conclude that complete BRSV virus can partially protect against a BRSV infection with a strain that contains an antigenic dissimilar G protein.

Serological and genetic characterisation of bovine respiratory syncytial virus (BRSV) indicates that Danish isolates belong to the intermediate subgroup: no evidence of a selective effect on the variability of G protein nucleotide sequence by prior cell culture adaption and passages in cell culture or calves

Danish isolates of bovine respiratory syncytial virus (BRSV) were characterised by nucleotide sequencing of the G glycoprotein and by their reactivity with a panel of monoclonal antibodies (MAbs). Among the six Danish isolates, the overall sequence divergence ranged between 0 and 3% at the nucleotide level and between 0 and 5% at the amino acid level. Sequence divergences of 7-8%, 8-9% and 2-3% (nucleotide) and 9-11%, 12-16% and 4-6% (amino acid) were obtained in the comparison made between the group of Danish isolates and the previously sequenced 391-2USA, 127UK and 220-69Bel isolates, respectively. Phylogenetic analysis showed that the Danish isolates formed three lineages within a separate branch of the phylogenetic tree. Nevertheless, the Danish isolates were closely related to the 220-69Bel isolate, the prototype of the intermediate antigenic subgroup. The sequencing of the extracellular part of the G gene of additional 11 field BRSV viruses, processed directly from lung samples without prior adaption to cell culture growth, revealed sequence variabilities in the range obtained with the propagated virus. In addition, several passages in cell culture and in calves had no major impact on the nucleotide sequence of the G protein. These findings indicated that the previously established variabilities of the G protein of RS virus isolates were not attributable to mutations induced during the propagation of the virus. The reactivity of the Danish isolates with G protein-specific MAbs were similar to that of the 220-69Bel isolate. Furthermore, the sequence of the immunodominant region was completely conserved among the Danish isolates on one side and the 220-69Bel isolate on the other. When combined, these data strongly suggested that the Danish isolates belong to the intermediate subgroup.

Antigenic structure of the central conserved region of protein G of bovine respiratory syncytial virus

Epitopes were resolved at the amino acid level for nine monoclonal antibodies (MAbs) directed against the central conserved region of protein G of bovine respiratory syncytial virus (BRSV-G). Peptide binding studies showed which amino acids in the epitope contributed to antibody binding. The details of the epitopes were compared with the high-resolution structure of a synthetic peptide corresponding to the central conserved region of BRSV-G, and this indicated which face of the central conserved region is the antigenic structure. The major linear epitope of the central conserved region of BRSV-G is located at the tip of the loop, overlapping a relatively flat surface formed by a double disulfide-bonded cystine noose. At least one, but possibly two sulfur atoms of a disulfide bridge that line the conserved pocket at the center of the flat surface, is a major contributor to antibody binding. Some of the residue positions in the epitope have mutated during the evolution of RSV-G, which suggests that the virus escaped antibody recognition with these mutations. Mutations that occur at positions 177 and 180 may have only a local effect on the antigenic surface, without influencing the structure of the backbone, whereas mutations at positions 183 and 184 will probably have major structural consequences. The study explains the antigenic, structural, and functional importance of each residue in the cystine noose which provides information for peptide vaccine design. Additionally, analysis of the epitopes demonstrated that two point mutations at positions 180 and 205 define the preliminary classification of BRSV subgroups.