Identifying bovine respiratory syncytial virus by reverse transcription-polymerase chain reaction and oligonucleotide hybridizations

Molecular characterization and comparison of diagnostic methods for bovine respiratory viruses (BPIV-3, BRSV, BVDV, and BoHV-1) in field samples in northwestern Turkey

The aim of this study was to evaluate the compatibility among virus isolation (VI), ELISA, and PCR for diagnosis of the major viral agents (BPIV-3, BRSV, BVDV, and BoHV-1) responsible for BRD in the field samples. For that purpose, a total of 193 samples (133 nasal swabs and 60 lung tissue samples) from cattle with respiratory signs in northwestern Turkey were examined. For VI, all the samples were inoculated at least 3 blind passages onto MDBK cell culture. In addition, the samples were tested by hemadsorption assay and RT-PCR for BPIV-3; nested RT-PCR for BRSV; immunoperoxidase monolayer assay, antigen-ELISA, and RT-PCR for BVDV; and antigen-ELISA and PCR for BoHV-1. The detected 1 (0.52%) BPIV-3 isolate was found to be in the genotype BPIV-3c. No BRSV isolate could be obtained, while 5 (2.59%) samples were evaluated positive in nested-RT PCR. The presence of BVDV antigen in 10 (5.18%) samples and the BVDV genome in 5 (2.59%) samples were detected, while non-cytopathogenic BVDV isolates were obtained only in 2 (1.04%) samples. The detected BVDV strains fell into the genetic clusters of BVDV-1a, -1f, and -1l. For detection of BoHV-1, although viral isolation and Ag-ELISA results were negative, presence of BoHV-1.1 genome was detected in 2 (1.04%) samples. By the results of VI, ELISA, and PCRs, 10.88% (21/193) of samples were found positive for the evaluated viruses. Depending on the obtained data, combined uses of the diagnostic methods were evaluated to be more reliable for routine diagnosis of bovine respiratory viruses.

Bovine respiratory syncytial virus

Bovine respiratory syncytial virus (BRSV) is a major cause of respiratory disease and a major contributor to the bovine respiratory disease (BRD) complex. BRSV infects the upper and lower respiratory tract and is shed in nasal secretions. The close relatedness of BRSV to human respiratory syncytial virus (HRSV) has allowed researchers to use BRSV and HRSV to elucidate the mechanisms by which these viruses induce disease. Attempted vaccine production using formalin-inactivated vaccine resulted in exacerbated disease when infants became exposed to HRSV. Cattle vaccinated with formalin-inactivated virus had enhanced disease when inoculated with BRSV. This article discusses various aspects of BRSV, its epidemiology, pathogenesis, diagnostic tests, immunity, and vaccination.

Evaluation of a commercial real-time reverse transcription polymerase chain reaction kit for the diagnosis of Bovine respiratory syncytial virus infection

Recently a commercial real-time reverse transcription polymerase chain reaction (RT-PCR) kit has been marketed for the detection of Bovine respiratory syncytial virus (BRSV). However, diagnostic interpretation of the results of this kit requires its comparison to commonly used methods. Therefore, the objective of this study was to evaluate the performance of this kit in comparison with the conventional direct fluorescent antibody test (FAT). Twenty BRSV strains and 14 heterologous bovine viruses were used to check the kit's sensitivity and specificity. The efficiency and detection limit of the kit were determined by testing dilution series of a BRSV strain. The comparison between real-time RT-PCR kit and FAT was performed with 94 clinical samples from calves with clinical signs of respiratory disease including lung tissues (n = 55), transtracheal aspiration samples (n = 20), and nasal swab samples (n = 19). All of the BRSV strains tested were detected by real-time RT-PCR. No cross-reaction was shown with the 14 heterologous bovine viruses. The real-time RT-PCR was 99.3% efficient with a detection limit of 0.1 TCID(50) (50% tissue culture infective dose). The results of real-time RT-PCR and FAT were concordant for 65 of the 94 clinical samples tested. The remaining 29 clinical samples were positive by real-time RT-PCR and negative by FAT, demonstrating the higher sensitivity of real-time RT-PCR. In conclusion, the kit evaluated in this study was sensitive, specific, and had a low threshold of detection. Furthermore, the use of this kit instead of FAT allows an improvement of the sensitivity for the detection of BRSV in clinical samples.

Detection by real-time RT-PCR of a bovine respiratory syncytial virus vaccine in calves vaccinated intranasally

Seventeen four- to five-week-old calves that were not shedding bovine respiratory syncytial virus (BRSV) were vaccinated intranasally against the disease and sampled by nasal swabbing on 16 different days for up to 20 days after vaccination. BRSV vaccine virus was detected in 15 of the 17 calves. Five of the calves were PCR positive on only one swab, eight were PCR positive on two to five swabs and two were PCR positive on more than five swabs. Twelve of the calves were positive only before day 14 and three were positive after day 14. The nasal shedding of BRSV vaccine virus was very variable.

Evaluation of a single-tube fluorogenic RT-PCR assay for detection of bovine respiratory syncytial virus in clinical samples

Bovine respiratory syncytial virus (BRSV) causes severe disease in naïve cattle of all ages and is a common pathogen in the respiratory disease complex of calves. Simplified methods for rapid BRSV diagnosis would encourage sampling during outbreaks and would consequently lead to an extended understanding of the virus. In this study, a BRSV fluorogenic reverse transcription PCR (fRT-PCR) assay, based on TaqMan principle, was developed and evaluated on a large number of clinical samples, representing various cases of natural and experimental BRSV infections. By using a single-step closed-tube format, the turn-around time was shortened drastically and results were obtained with minimal risk for cross-contamination. According to comparative analyses, the detection limit of the fRT-PCR was on the same level as that of a nested PCR and the sensitivity relatively higher than that of a conventional PCR, antigen ELISA (Ag-ELISA) and virus isolation (VI). Interspersed negative control samples, samples from healthy animals and eight symptomatically or genetically related viruses were all negative, confirming a high specificity of the assay. Taken together, the data indicated that the fRT-PCR assay can be applied to routine virus detection in clinical specimens and provides a rapid and valuable tool in BRSV research.

Detection and quantitation of bovine respiratory syncytial virus using real-time quantitative RT-PCR and quantitative competitive RT-PCR assays

A single tube, fluorogenic probe-based, real-time quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) assay was developed for detection and quantitation of bovine respiratory syncytial virus (BRSV) using BioRad's iCycler iQ. Real-time Q-RT-PCR was compared with quantitative competitive RT-PCR (QC-RT-PCR) and viral titers. Viral mRNA levels were measured in BRSV-infected bovine turbinate cell lysate harvested at eight time points (1.5, 6, 12, 24, 36, 48, 60, 72 h) post-infection. A homologous BRSV cRNA standard was used for quantitation of the mRNA by plotting a standard curve of cycle threshold (Ct) values versus standard 10-fold dilutions of cRNA of known concentrations. Detection as low as 171 copies/microl of standard BRSV cRNA was possible. For QC-RT-PCR, a competitor RNA molecule having a deletion was designed and used for quantitation of the BRSV viral mRNA. The results of real-time Q-RT-PCR and QC-RT-PCR assays showed a positive correlation. Real-time Q-RT-PCR was a sensitive, specific, rapid, and efficient method that eliminates the post-PCR processing steps when compared to QC-RT-PCR. Quantitation of BRSV using real-time Q-RT-PCR will have application in studies aimed at understanding the pathogenesis of BRSV.

In situ hybridization detection of bovine respiratory syncytial virus in the lung of experimentally infected lambs

We studied the distribution of bovine respiratory syncytial virus (BRSV) RNA in lungs of experimentally inoculated lambs by in situ hybridization at different times postinoculation. The probe used for in situ hybridization was prepared by reverse transcription of BRSV RNA, followed by polymerase chain reaction (PCR) amplification of the cDNA. Twenty-five Merino lambs of both sexes with a live weight of 17 +/- 3 kg received an intratracheal inoculation of 20 ml saline solution containing 1.26 X 10(6) TCID50 BRSV (strain NMK7)/ml. Lambs were slaughtered 1, 3, 7, 11, and 15 days postinoculation (PID). Bronchial and bronchiolar epithelial cells were positive for BRSV nucleic acid by ISH at 1, 3, 7, and 11 PID. However, alveolar epithelial cells contained positive cells at 1, 3, and 7 PID. Cells containing viral RNA were detected from 1 to 11 PID in exudate within bronchial and bronchiolar lumina and from 3 to 7 PID in alveolar exudates. Positive hybridization signals were identified in interstitial mononuclear cells and in bronchi-associated lymphoid tissue from 3 to 11 PID. Mononuclear cells were located in peribronchiolar tissue and interalveolar septa. The highest signal intensity in positive cells was observed at 3 and 7 PID, coinciding with the most important histopathological findings.

Evaluation of a nested reverse transcription-PCR assay based on the nucleoprotein gene for diagnosis of spontaneous and experimental bovine respiratory syncytial virus infections

The first nested reverse transcription (RT)-PCR based on the nucleoprotein gene (n RT-PCR-N) of the bovine respiratory syncytial virus (BRSV) has been developed and optimized for the detection of BRSV in bronchoalveolar lavage fluid cells of calves. This test is characterized by a low threshold of detection (0.17 PFU/ml), which is 506 times lower than that obtained by an enzyme immunosorbent assay (EIA) test (RSV TESTPACK ABBOTT). During an experimental infection of 17 immunocompetent calves less than 3 months old, BRSV RNA could be detected up to 13 days after the onset of symptoms whereas isolation in cell culture was possible only up to 5 days. Compiling results obtained by conventional techniques (serology, antigen detection, and culture isolation) for 132 field samples collected from calves with acute respiratory signs revealed that n RT-PCR-N showed the highest diagnostic sensitivity and very good specificity. This n RT-PCR-N with its long period of detection during BRSV infection thus provides a valuable tool for diagnostic and epidemiological purposes.

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.

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.

Respiratory syncytial virus infection in the elderly

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infections in infants and children throughout the world. Respiratory syncytial virus infections in the elderly represent reinfections in the hosts who have had many prior episodes. Thus, RSV infections are usually not considered serious in adults, since reinfections are generally known to result in mild disease. Nevertheless, in adults, as in children, the infection has been reported to cause altered airway resistance and exacerbation of chronic obstructive lung disease. In people over 60 years of age, RSV usually causes mild nasal congestion, but can also result in fever, anorexia, pneumonia, bronchitis, and even death. Diagnosis of RSV infection in the elderly by the standard methods used in children is not as successful as in the latter group. This may be due to a combination of factors such as shorter shedding phase, lower viral titers, and dry mucosa. An alternative, rapid, and direct viral diagnostic method, the polymerase chain reaction, has recently been introduced in the diagnosis of RSV infections.

Applications of DNA amplification techniques in veterinary diagnostics

An overview of the principles of the polymerase chain reaction, ligase chain reaction, self-sustained sequence replication and Q beta replicase is given. The application of these methods for the diagnosis of veterinary infectious and hereditary diseases as well as for other diagnostic purposes is discussed and comprehensive tables of reported assays are provided. Specific areas where these DNA-based amplification methods provide substantial advantages over traditional approaches are also highlighted. With regard to PCR-based assays for the detection of viral pathogens, this article is an update of a previous review by Belák and Ballagi-Pordány (1993).

Development of nested PCR assays for detection of bovine respiratory syncytial virus in clinical samples

Two nested PCR assays were developed for the detection of bovine respiratory syncytial virus (BRSV). Primers were selected from the gene encoding the F fusion protein (PCR-F) and the gene encoding the G attachment protein (PCR-G). Biotinylated oligonucleotide probes, termed F and G, were selected for the hybridization of the respective PCR products. The sensitivities of the PCR-F and PCR-G assays were similar, both detecting 0.1 tissue culture infective dose of the virus. The PCR-F assay amplified all bovine strains and one human strain (RS32) tested. No cross-reactions were observed with nine heterologous respiratory viruses. PCR-F products of bovine and human RSV strains were discriminated by using endonuclease restriction enzyme ScaI, which specifically cleaved, products of BRSV. Oligonucleotide probe F was also specific for products of BRSV. The PCR-G assay detected all bovine strains and none of the human strains tested. A faint electrophoretic band was also observed with products of Sendai virus. However, probe G did not hybridize with this product, only with products of BRSV. Nasal swabs collected from cattle with no symptoms and cattle in the acute stage of respiratory disease were analyzed for BRSV by the immunofluorescence (IF) method and by the PCR-F and PCR-G assays. The virus was detected by the PCR assays in 31 of 35 (89%) samples tested. Only 23 samples (66%) were positive by the IF method, and these samples were also positive by both the PCR-F and PCR-G assays. The 31 samples detected as positive by PCR originated from cattle presenting clinical signs of acute respiratory disease; the four PCR-negative samples originated from clinically asymptomatic neighboring cattle. All sampled animals subsequently seroconverted and became reactive to BRSV. Thus, the detection of BRSV by PCR correlated with clinical observations and was considerably more sensitive (66 versus 89%) than IF. These results indicate that both nested PCR assays provide rapid and sensitive means for the detection of BRSV infection in cattle. Considering its higher specificity, the PCR-F assay can be recommended as the method of choice in the analysis of clinical specimens of BRSV.

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.