Bovine respiratory syncytial virus: host range in laboratory animals and cell cultures

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.

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.

Structural difference in the fusion protein among strains of bovine respiratory syncytial virus

The polypeptides of different strains of bovine respiratory syncytial virus (RSV) were compared. Altered electrophoretic migrations were observed in the G, F, P, M and 22 kDa polypeptides. The molecular weight of the F2 fragment in human RSV (Long strain) and bovine RSV (A51908 and Md-X strains) was approximately 20 kDa whereas it was approximately 15.5 kDa in caprine RSV and bovine RSV (FS-1 and VC-464 strains). The size difference of the F2 subunit was due to difference in the extent of glycosylation.

Gene junction sequences of bovine respiratory syncytial virus

The nucleotide sequences of seven gene junctions (N-P, P-M, M-SH, SH-G, G-F, F-M2 and M2-L) of bovine respiratory syncytial virus (BRSV) strain A51908 were determined by dideoxynucleotide sequencing of cDNAs from polytranscript mRNAs and from genomic RNA. By comparison with the consensus sequences derived from human respiratory syncytial virus (HRSV) mRNAs, gene-start and gene-end sequences were found in all BRSV mRNAs. There was a perfect match between the BRSV and HRSV in all gene-start sequences, except for the sequence of the SH gene which contained one nucleotide difference compared to HRSV A2; and the gene-start sequence of the L gene, which was one nucleotide shorter than the corresponding sequence of HRSV. Analysis of the intergenic regions showed a high degree of divergence in the nucleotide sequence between BRSV and HRSV. However, the length of the nucleotides in the intergenic sequences was similar for a given gene junction. As in the case of HRSV, the M2 and L genes of BRSV overlap by 68 nucleotides, suggesting a similar transcription attenuation mechanism. The sequences of the overlap, corresponding to the 3' end of the L gene, were almost identical between BRSV and HRSV.

Molecular cloning and sequence analysis of bovine respiratory syncytial virus mRNA encoding the major nucleocapsid protein

The nucleotide sequence of the gene encoding the major nucleocapsid (N) protein of bovine respiratory syncytial virus (BRSV) has been determined. The N mRNA is 1196 nucleotides long with a single, large open reading frame. The derived polypeptide has 391 amino acids corresponding to a calculated molecular weight of 42,600 Da. This is in agreement with the molecular weight of 43,000 Da determined for the BRSV N protein by SDS-polyacrylamide gel electrophoresis (PAGE). Comparison of the nucleotide sequence of BRSV N gene with the sequence of the N gene of human respiratory syncytial virus (HRSV) revealed a homology of 80.7%. There is a 93.3% homology at the amino acid level between the N proteins of BRSV and HRSV. The 5'- and 3'-terminal untranslated sequences that are conserved among HRSV mRNAs were also identified in the N mRNA of BRSV. The results indicate that the N genes are highly conserved in the bovine and human strains of respiratory syncytial virus.

Nucleotide sequence analysis and expression from recombinant vectors demonstrate that the attachment protein G of bovine respiratory syncytial virus is distinct from that of human respiratory syncytial virus

Bovine respiratory syncytial (BRS) virus causes a severe lower respiratory tract disease in calves similar to the disease in children caused by human respiratory syncytial (HRS) virus. While there is antigenic cross-reactivity among the other major viral structural proteins, the major glycoprotein, G, of BRS virus and that of HRS virus are antigenically distinct. The G glycoprotein has been implicated as the attachment protein for HRS virus. We have carried out a molecular comparison of the glycoprotein G of BRS virus with the HRS virus counterparts. cDNA clones corresponding to the BRS virus G glycoprotein mRNA were isolated and analyzed by dideoxynucleotide sequencing. The BRS virus G mRNA contained 838 nucleotides exclusive of poly(A) and had a major open reading frame coding for a polypeptide of 257 amino acid residues. The deduced amino acid sequence of the BRS virus G polypeptide showed only 29 to 30% amino acid identity with the G protein of either the subgroup A or B HRS virus. However, despite this low level of identity, there were strong similarities in the predicted hydropathy profiles of the BRS virus and HRS virus G proteins. A cDNA molecule containing the complete BRS virus G major open reading frame was inserted into the thymidine kinase gene of vaccinia virus by homologous recombination, and a recombinant virus containing the BRS virus G protein gene was isolated. This recombinant virus expressed the BRS virus G protein, as demonstrated by Western immunoblot analysis and immunofluorescence of infected cells. The BRS virus G protein expressed from the recombinant vector was transported to and expressed on the surface of infected cells. Antisera to the BRS virus G protein made by using the recombinant vector to immunize animals recognized the BRS virus attachment protein but not the HRS virus G protein and vice versa, confirming the lack of antigenic cross-reactivity between the BRS and HRS virus attachment proteins. On the basis of the data presented here, we conclude that BRS virus should be classified within the genus Pneumovirus in a group separate from HRS virus and that it is no more closely related to HRS virus subgroup A than it is to HRS virus subgroup B.

Analysis of polypeptides synthesized in bovine respiratory syncytial virus-infected cells

Ten virus-specific polypeptides ranging in molecular weight from approximately 200k to 11k were identified in bovine respiratory syncytial virus (BRSV-)infected cells. Time course analysis of the induction of the viral polypeptides indicated that they could be detected as early as 30 min post-infection and their synthesis reached a plateau 12 h after infection. Cell free translation of total infected-cell mRNA in a rabbit reticulocyte system yielded 7 proteins corresponding in size to virus-specific proteins synthesized in BRSV-infected cells. The P protein was highly phosphorylated; G and F were identified as glycoproteins by [3H]glucosamine labeling. Glycosylation of G protein was largely resistant to tunicamycin, suggesting that the majority of the carbohydrate residues are attached via O-glycosidic bonds, whereas the F protein was N-linked glycosylated. Tunicamycin caused a drastic reduction in the yield of infectious virus titer indicating that the carbohydrate moieties serve a critical role in the infectious cycle of BRSV.

Immunity to human and bovine respiratory syncytial virus

Human and bovine respiratory syncytial viruses resemble each other closely. During annual winter outbreaks, they cause similar respiratory tract disease in infants and calves. The disease is most severe in children and calves between 1 and 3 months old, when maternal antibodies against the virus are usually present. Reinfections, which are common, are accompanied by progressively milder illnesses in children, but are symptomless in calves. Because maternal antibodies suppress serum and mucosal antibody responses of all isotypes, the development of a vaccine that is effective in young children and calves with high levels of maternal antibodies has been severely hampered. Although virus administered intranasally to young calves with maternal antibodies does not evoke antibody responses, it can prime these calves for a protective memory response upon reinfection. Protection appears to be associated with the capacity to mount a mucosal memory IgA response. There are several indications that one or more immunopathologic mechanisms contribute to the disease. An Arthus reaction (type III) may have a role in the pathogenesis, because activated complement may cause most of the pathologic lesions, including edema and emphysema in uninfected parts of the lung. Lungs from calves with severe or fatal disease have depositions of complement component C3 and a low histamine content. The most immunogenic and protective antigen of the virus is the fusion (F) glycoprotein, which evokes a strong antibody response and is a target for cytotoxic T cells. On the F protein, epitopes that induce neutralizing and non-neutralizing antibodies, both of which may enhance complement activation, were identified. Immunity to the F protein may have beneficial and harmful effects.

Hemagglutination of epizootic hemorrhagic disease virus

Hemagglutination of epizootic hemorrhagic disease virus (EHDV) with a variety of erythrocyte species at 4 degrees C, room temperature and 37 degrees C was dependent on the NaCl molarity and the pH of the diluent. The hemagglutination inhibition test was used to identify EHDV serotypes.