Identification of subgroups of bovine respiratory syncytial virus

Investigation of viral pathogens in cattle with bovine respiratory disease complex in Inner Mongolia, China

As a multifactor disease, the bovine respiratory disease complex (BRDC) causes high morbidity and mortality that is devastating to the cattle industry. To assess viral infections in beef cattle suffering from respiratory diseases in Inner Mongolia, 302 nasal swabs and serum samples were randomly collected from cattle with mild respiratory symptoms between March 2018 and May 2019. Our results showed that the rate of RT-PCR results positive for nucleic acids of viral pathogens in 6 cities was between 54 and 80%.The rates of bovine viral diarrhea virus (BVDV), bovine herpesvirus 1 (BHV-1), bovine parainfluenza virus type 3(BPIV3), and bovine respiratory syncytial virus(BRSV)infections were 44.70% (135/302), 24.83% (75/302), 5.63% (17/302), and 6.95% (21/302),respectively. There are also 8.94% (27/302) of samples were positive for BVDV and BHV-1, and 3.97% (12/302) of samples were positive for BPIV3 and BRSV. In addition, the RT-PCR products were sequenced, and phylogenetic analysis based on these sequences was performed. The results indicated that: a) all of the BVDV isolates were BVDV-1 and were classified as BVDV-1a (66.67%) and BVDV-1b (33.33%); b) all of the BHV-1 isolates were classified as subtype 1.1; 44.44% of the isolates were closely related to modified live viral vaccine strains, and 55.56% of the isolates were closer to epidemic strains; c) all of the BPIV3 isolates belonged to BPIV3c; d) all of the BRSV isolates were classified into subgroup III. It is suggested that an important cause of respiratory diseases for beef cattle is viral infection, and phylogenetic analysis can help us choose the proper strain to develop a vaccine.

Epidemiology, molecular epidemiology and evolution of bovine respiratory syncytial virus

The bovine respiratory syncytial virus (BRSV) is an enveloped, negative sense, single-stranded RNA virus belonging to the pneumovirus genus within the family Paramyxoviridae. BRSV has been recognized as a major cause of respiratory disease in young calves since the early 1970s. The analysis of BRSV infection was originally hampered by its characteristic lability and poor growth in vitro. However, the advent of numerous immunological and molecular methods has facilitated the study of BRSV enormously. The knowledge gained from these studies has also provided the opportunity to develop safe, stable, attenuated virus vaccine candidates. Nonetheless, many aspects of the epidemiology, molecular epidemiology and evolution of the virus are still not fully understood. The natural course of infection is rather complex and further complicates diagnosis, treatment and the implementation of preventive measures aimed to control the disease. Therefore, understanding the mechanisms by which BRSV is able to establish infection is needed to prevent viral and disease spread. This review discusses important information regarding the epidemiology and molecular epidemiology of BRSV worldwide, and it highlights the importance of viral evolution in virus transmission.

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.

Analysis of ruminant respiratory syncytial virus isolates by RNAse protection of the G glycoprotein transcripts

Two different respiratory syncytial virus (RSV) radiolabeled probes were used to characterize the genetic heterogeneity of 25 ruminant RSV isolates by the ribonuclease protection assay. A 32P-radiolabeled antisense RNA probe was transcribed from cloned ovine and bovine RSV G glycoprotein genes and then hybridized with total RNA isolated from infected cells with various ruminant RSV isolates. The results of this study, along with previously published nucleotide sequence data of the ovine RSV G glycoprotein gene, suggest the presence of at least 2 ruminant RSV subgroups. One subgroup is represented by RSV isolated from respiratory disease outbreaks from calves and goats, and the other is represented by RSV isolated from sheep.

A comparison of diagnostic methods for the detection of bovine respiratory syncytial virus in experimental clinical specimens

Virus shedding was monitored in nasal secretions of 12 calves experimentally infected with bovine respiratory syncytial virus (BRSV) using an antigen capture enzyme-linked immunosorbent assay (ELISA) detecting the nucleoprotein (NP) antigen of BRSV, by a polymerase chain reaction (PCR) amplifying the fusion protein of BRSV, and by a microisolation assay combined with immunoperoxidase staining for the F protein of BRSV. Under the conditions of this study, similar limits of detection and quantitative results were obtained from all three assays. BRSV was detected in nasal secretions of all calves for a minimum of 4 d. Virus shedding began on Day 2 after infection, peaked on Days 3-5, and was cleared in most calves by Day 8. The PCR, and to a lesser extent the ELISA, may detect virus shedding for a longer period after infection than virus isolation, possibly due to neutralization of the virus by rising mucosal antibody. Simulated environmental conditions likely to be experienced during transport of clinical field specimens markedly reduced the sensitivity of virus isolation but had a minimal effect on the results of the NP ELISA. Actual field transport conditions (overnight on ice) had minimal apparent effect on the results of the PCR assay. The less stringent specimen handling requirements, combined with low limits of detection, of both the nucleoprotein ELISA and PCR, indicate either of these assays are more suitable for diagnostic applications than virus isolation.

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.

Bovine respiratory syncytial virus

Since the first report of BRSV in the 1970s, the understanding of this agent and its respective disease has increased dramatically. Current evidence supports a major role for this virus in bovine respiratory disease. Advances in diagnostics have increased the ability to demonstrate this virus in field outbreaks of respiratory disease. The clinical signs and pathologic features have been well described, and vaccines are available to aid in prevention and control. Still, many questions remain to be answered with respect to BRSV. It appears there may be antigenic subgroups of BRSV, but the epidemiologic significance and relevance to immunization of this remains unknown. The question of differences in virulence among isolates of this virus has yet to be addressed. From an epidemiologic standpoint, the means by which BRSV perpetuates in the cattle population has yet to be elucidated. Although progress has been made in understanding the pathogenesis and immune response to BRSV, the mechanism of disease production and immune protection is incomplete. Lastly, efficacy testing of existing vaccines need to continue, as well as the development of new vaccines and new approaches to vaccination.

Analysis of the bovine respiratory syncytial virus fusion protein (F) using monoclonal antibodies

Seven monoclonal antibodies (MAbs) directed against bovine respiratory syncytial virus (BRSV) fusion (F) protein were produced and characterized by radioimmunoprecipitation and immunofluorescence assays. These seven MAbs together with the previously described MAbs (Beeler and Van Wyke Coelingh, 1989) to the F protein of human respiratory syncytial virus (HRSV) were used to study the antigenic variation of 12 strains of ungulate RSV. All except one MAbs specific for the HRSV-F protein reacted with ungulate RSV strains less efficiently, indicating that some epitopes are conserved, and others are not conserved on the F proteins of HRSV and BRSV strains. Three MAbs specific to the BRSV-F protein neutralized virus infectivity and reacted with all the ungulate RSV strains, suggesting that these epitopes are well conserved. Based on the reactivity of three other MAbs specific to the BRSV-F protein, ungulate RSVs could be grouped into two subgroups. The results indicated that there are antigenic variations in the F protein among ungulate RSV strains.

Immunization with a peptide derived from the G glycoprotein of bovine respiratory syncytial virus (BRSV) reduces the incidence of BRSV-associated pneumonia in the natural host

Previous reports demonstrate that synthetic peptides corresponding to the amino acid region 174-187 of G glycoprotein from subgroups A and B human respiratory syncytial virus (HRSV), containing a Cys-->Ser substitution at position 186, confer complete resistance to immunized BALB/c mice against infection with the respective virus. In this report, we show that a Cys186-->Ser substituted peptide (BG/174-187) representing the corresponding region of the bovine (B) RSV G glycoprotein conferred complete protection of mice against BRSV challenge, suggesting that the 174-187 region of RSV G glycoproteins constitutes a dominant protective epitope which has been maintained throughout evolution. Furthermore, immunization of calves with peptide BG/174-187 efficiently induced the production of antibodies capable of recognizing both the parental G glycoprotein and peptide BG/174-187. Following challenge with live BRSV, although none of the animals were protected from upper respiratory tract disease, there were little or no gross pneumonic lesions in the four peptide-immunized calves. In contrast, moderate to extensive pneumonic lesions were observed in 2 out of 3 calves in the control group. Our results thus suggest that peptide BG/174-187 efficiently prevented BRSV-associated pneumonia in the natural host. The use of this system as a model is quite promising with regard to the development of a human synthetic vaccine.

Sequence conservation in the attachment glycoprotein and antigenic diversity among bovine respiratory syncytial virus isolates

Partial nucleotide sequences were determined from the coding regions of the attachment glycoprotein (G) mRNAS of eight isolates of bovine respiratory syncytial virus (BRSV). The antigenic characteristics of 18 field and reference isolates were analyzed using the reactivity patterns of monoclonal antibodies (MAbs) directed against the human respiratory syncytial virus (HRSV) and BRSV G. fusion protein (F), nucleoprotein (N), and phosphoprotein (P), by radioimmunoprecipitation and immunofluorescence assays. The MAb reaction patterns demonstrated some random antigenic differences among the isolates, but for the most part were cross-reactive to the viral protein epitopes, especially on the F protein. Structural differences in the F and P proteins were observed among BRSV isolates; the P protein migrated at three different apparent molecular weights on PAGE gels. Antigenic and structural variation occurs among isolates, however, the structural differences in the P protein did not correlate with the antigenic differences among the F, N and P proteins. The G mRNA nucleotide sequence identities were high, ranging from 94.1 to 99.9%, and the predicted amino acid sequence identities ranged from 89.9 to 99.6%. Variance was due to substitution point mutations. The G protein ectodomains contained areas of sequence divergence flanking a highly conserved region, with four cysteine residues, which is analogous to the putative HRSV receptor binding domain. The high sequence and amino acid identities and random antigenic diversity among the isolates indicates that the BRSV isolates analyzed belong in a monophyletic group.

Subgrouping of bovine respiratory syncytial virus strains detected in lung tissue

Bovine respiratory syncytial virus is an important respiratory pathogen in cattle. Recently, subgroups of BRSV have been identified, based on antigenic differences. However, little is known about subgroups of BRSV that circulate in the cattle population. Therefore, we determined the reactivity of monoclonal antibodies (mAbs), directed against the G, F, or P protein of BRSV, with lung tissue from 47 calves, that suffered from severe respiratory disease. Fourteen animals (30%) proved to be infected with BRSV, because they all reacted with mAbs against the P or F protein, as detected by fluorescent antibody tests. Monoclonal antibodies against the G protein were able to discriminate between the BRSV-positive specimens: 7 strains were identified as subgroup A strains, and 5 strains as subgroup AB, which is introduced as BRSV subgroup in this paper. Two strains could not be identified unambiguously. It is concluded that BRSV subgroup A and AB were associated with severe respiratory disease, and that strains belonging to either subgroup circulated concurrently in the cattle population in the Netherlands.

Severe respiratory disease in dairy cows caused by infection with bovine respiratory syncytial virus

Outbreaks of severe respiratory disease caused by bovine respiratory syncytial virus (BRSV) were recorded in dairy herds throughout Sweden in 1988 and subsequently. The virus was demonstrated in nasopharyngeal swab material from animals in the acute stage of the disease by culture, the polymerase chain reaction (PCR) and by immunofluorescence. Serological data from the herds investigated showed that the cows had seroconverted to BRSV rather than to bovine coronavirus, bovine viral diarrhoea virus or parainfluenza-3 virus. It was predominantly dairy herds in isolated areas that contracted a severe primary BRSV infection, often after the purchase of new animals. A nationwide survey for BRSV antibodies in bulk milk samples showed the highest prevalence, of 84 to 89 per cent, in the southernmost regions of Sweden and the lowest prevalence, of 41 to 51 per cent, in the north of the country. The prevalence of BRSV was highest in areas with the highest populations of cattle.

A model for respiratory syncytial virus (RSV) infection based on experimental aerosol exposure with bovine RSV in calves

Five conventionally kept calves aged between 17 and 24 days were experimentally infected with bovine respiratory syncytial virus (BRSV) by aerosol in order to mimic the natural infection route. The calves were killed and autopsies performed 7 days after the first virus challenge. The BRSV isolate used induced tracheitis, bronchitis and atelectasis in infected calves. The only virus which could be isolated from the lungs of the calves was BRSV. In addition, Mycoplasma bovirhinis was isolated from the lungs or/and trachea of two calves. The clinical and histopathological findings, as well as the detection of BRSV antigens by immunofluorescence in the epithelial cells of lung and trachea, and the reisolation of the virus from bronchoalveolar lavage fluids of all inoculated calves, provided confirmation of successful infection with BRSV.

Development and application of a microneutralization ELISA for the detection of antibodies to bovine respiratory syncytial viruses

A microneutralization enzyme-linked immunosorbent assay (ELISA) was developed to detect specific antibodies to bovine respiratory syncytial viruses (BRSVs) in cattle sera using a monoclonal antibody to the fusion protein of the virus. Serum from 20 naturally exposed, 24 experimentally infected, and 15 immunized cattle were evaluated using 3 different BRSV isolates. Antibody titers determined with the microneutralization ELISA were compared with those derived from a classical virus neutralization assay, an indirect ELISA, and a fusion inhibition assay. These studies demonstrated a high degree of correlation (usually 0.90) among the assays. Furthermore, the results showed that immunization of cattle with one isolate (subgroup) of BRSV induced antibody responses that cross-reacted with at least 2 disparate isolates. These results document the utility of the microneutralization ELISA in assessing functionally important antibody responses to BRSVs in cattle.

Respiratory syncytial virus infections in human beings and in cattle

Respiratory syncytial virus (RSV) causes yearly outbreaks of respiratory disease in human beings and cattle all over the world. Most severe human respiratory syncytial virus (HRSV)-associated disease is observed in children less than 1 year of age while most severe bovine respiratory syncytial virus (BRSV)-associated disease is observed in calves less than 6 months of age. Two subgroups of HRSV have been identified. The existence of two subgroups of BRSV has been repeatedly suggested but is not yet well established. BRSV and HRSV are closely related antigenically but antigenic differences have been observed. Seasonal periodicity of RSV infection is usual with highest incidences in autumn and winter. Stress such as caused by movement, crowding and temperature changes are considered to play a role in bovine outbreaks. Human beings and cattle are the natural hosts of HRSV and BRSV, respectively. Primarily infected individuals are the most important source of RSV during outbreaks. The role of other species in the spread of HRSV and BRSV is unknown. Protective efficacy of maternally derived antibodies is considered to be incomplete. Such antibodies do not reduce shedding of virus after HRSV and BRSV infection. RSV is often transmitted by contact with nasal secretions but may also be transmitted by aerosols. Seroprevalence of HRSV and BRSV among adult human beings and cattle is over 70% and is always higher than it is among younger individuals. Both human beings and cattle of all ages may be reinfected with RSV. During BRSV reinfections, signs of respiratory tract disease and shedding of virus are seldom observed whereas these are common during HRSV reinfections. Persistent HRSV and BRSV infections in human beings and cattle have been suggested but have not so far been reported.

Dynamics of bovine respiratory syncytial virus infections: a longitudinal epidemiological study in dairy herds

To study the epidemiology of respiratory syncytial virus (RSV) infections during the year, the incidences of primary infections and reinfections were monitored by titrating antibodies to bovine RSV (BRSV) in cattle above 2 months of age in 6 dairy herds in the Netherlands. From August 1990 until September 1991, 884 cattle were sampled at one-month intervals. A total of 155 cattle, most under two years of age, had a primary antibody response. Antibody rises were found in 259 cattle of all ages. The highest incidences of BRSV infections were found in one period either in autumn or winter. In other seasons, primary infections were rare, whereas reinfections were not uncommon. In 5 out of the 6 herds, two seronegative sentinel calves were introduced at the end of the winter and none developed specific antibodies before the next winter. The observations strongly suggest that, in spite of regular reinfections, BRSV circulates during spring or summer at a very low level or not at all. Persistent BRSV infection in a number of cows might be a means for the virus to survive during summer, but a steady rate of reinfection of seropositive cows throughout the year at a low level might also maintain a reservoir of infectious virus. This study adds to the knowledge of frequency and timings of primary infections and reinfections of BRSV and it might contribute to the study of these issues of human RSV.

Characteristic differences in reverse transcription-polymerase chain reaction products of ovine, bovine, and human respiratory syncytial viruses

In reverse transcription-polymerase chain reactions (RT-PCR) and DNA hybridizations using primers and an oligonucleotide probe to the fusion (F) protein mRNA of bovine respiratory syncytial virus (BRSV), all the BRSV isolates and a goat isolate could be distinguished from prototype isolates of human respiratory syncytial viruses (HRSV) and ovine (sheep and bighorn sheep) respiratory syncytial viruses (RSV). However, RT-PCR amplifications with primers to sequences of the HRSV F protein mRNA resulted in amplified products of approximately 243 bp if mRNA templates of subgroup A HRSV strains were present and slightly larger amplified products with subgroup B HRSV strains. No amplified products were observed in HRSV-primed RT-PCR with BRSV or goat or ovine RSV mRNA templates. Although the ovine RSV isolates were antigenically cross-reactive with the goat RSV, HRSV and BRSV isolates, they were no amplified with either HRSV- or BRSV-specific primers in RT-PCR. These results confirm previous immunological comparisons suggesting that some ovine RSV isolates should be considered as distinct respiratory syncytial viruses.