Biotinylated and radioactive cDNA probes in the detection by hybridization of bovine enteric coronavirus

Bovine coronavirus

This review aims to summarize current data describing the characteristics of bovine coronavirus (BCV) and the three clinical syndromes with which this virus is associated. The first half of this paper consists of a general description of the virus, commencing with a brief outline of the methods used for in vitro growth. The structure of the virus is then described in more detail, with particular reference to the structure and functions of the four major viral proteins. This is followed by an outline of the unique replication strategy adopted by coronaviruses. The second half of this review discusses the clinical significance of the virus, beginning with a detailed account of BCV-induced neonatal calf diarrhoea, the clinical syndrome with which this virus is most commonly associated. The clinical and epidemiological importance of BCV respiratory tract infection is then discussed, and finally the evidence supporting the aetiological role of BCV in outbreaks of winter dysentery in adult cattle is examined.

Radioactive and enzymatic cloned cDNA probes for bovine enteric coronavirus detection by molecular hybridization

Genomic RNA of F15 strain bovine enteric coronavirus (BECV) was cloned in E. coli. Three clones (174, 160, PG78), selected in the cDNA library, including a large portion of the nucleocapsid (N), matrix (M) and peplomeric (S) protein genes, were used as probes for a slot blot hybridization assay. Two probe labelling techniques were compared, radiolabelling with 32P and enzymatic labelling through covalent linkage to peroxidase and chemiluminescence detection. The radioactive probe 174 detected as little as 1 to 3 pg of viral RNA, while the less sensitive enzymatic probe could not reveal more than 100 pg of RNA. No significant detection amplification was achieved when a mixture of the three probes was used. Probe 174 allowed specific identification for BECV. No hybridization was noticed either with rotaviruses or even with other antigenically unrelated members of the family Coronaviridae such as transmissible gastroenteritis virus. The test proved valid for detection of BECV in the supernatant of infected HRT-18 cells: genomic RNA could be detected after direct spotting of samples, but prior nucleic acid extraction after proteinase K treatment improved virus detection. BECV diagnosis in faecal samples using enzymatic probe was compared with conventional diagnostic methods.

Genomic relationship between turkey and bovine enteric coronaviruses identified by hybridization with BCV or TCV specific cDNA probes

Genomic relationships between turkey and bovine coronavirus (TCV and BCV), which are currently placed in distinct antigenic groups, were demonstrated by hybridization using specific cDNA probes. BCV-specific recombinant plasmid probes p 52, p 27, and p 247, holding inserts derived from (probably nonstructural) genes, and plasmids pN 17 and pN 9 holding the N and M gene, respectively, permitted the detection of isolates of both BCV and TCV with similar sensitivities. Similarly, probing supernatants of cell cultures infected with several isolates of TCV, using probes pN 17 and pM 78, respectively holding the N gene of BCV and TCV, resulted in equally intense detection signals. Only a slight detection of MHV-3, which is antigenically related to BCV, was observed, whereas the probes did not allow the detection of IBV, TGEV, and HCV-229E, which are placed in antigenic groups separate from those of BCV and TCV. Detection of TCV was improved by hybridization with BCV-specific single-stranded (ss) probes holding sequences of the N and M genes and synthesized by the polymerase chain reaction. Diagnosis of TCV in 134 clinical samples by hybridization was better with PCR-produced ss BCV-specific probes than with ds PCR-produced probes or a combination of six recombinant plasmid probes holding non-overlapping BCV-specific cDNA sequences. Detection signals were absent when probing clinical samples with 32P-labelled pUC-DNA.

Polymerase chain reaction for probe synthesis and for direct amplification in detection of bovine coronavirus

The polymerase chain reaction (PCR) was used to synthesize ds and ss probes for the detection of bovine coronavirus (BCV) using recombinant plasmids as template molecules. The ds probes detected a minimum of about 2 X 10(5) viral genomes after exposure for 1 h, a detection limit similar to nick-translated probes after exposure of the films for 60 h. More than 8 h exposure to blots probed with these ds probes resulted in complete darkening of the film. The ss probes, synthesized by asymmetric PCR on linearized plasmids, permitted the detection of 5 X 10(4) genomes, which equalled the capacity of random-primed probes. Prolonged exposure did not increase the background as in case of ds PCR-probed blots. Probes, synthesized by asymmetric PCR and random-priming were labeled to similar specific activities and were better in terms of sensitivity and detectability as opposed to nick-translated probes. However, the specificity of detection with ss probes as to random primed probes was increased further. About 10 viral genomes, after fragment-specific amplification by PCR, were detected by agarose-gel analysis. PCR-probe synthesis was simple, highly reproducible, and allowed the synthesis of probes for specific fragments.

Antigenic and genomic relationships among turkey and bovine enteric coronaviruses

Antigenic and genomic relationships among tissue culture-adapted turkey enteric coronavirus (TCV) isolates, three strains of avian infectious bronchitis virus (IBV), and mammalian coronaviruses were investigated. Immunoblotting and immunoprecipitation experiments using polyclonal antisera showed that the four major structural proteins of TCV cross-reacted with the four homologous proteins of bovine enteric coronavirus (BCV), the N and M proteins of mouse hepatitis virus serotype 3, and the N protein of IBV. Close antigenic relationships between TCV and BCV were also established by seroneutralization and hemagglutination-inhibition. Of 49 monoclonal antibodies produced against either TCV or BCV, 11 differentiated the two viruses. Five of these monoclonal antibodies had neutralizing activities and were directed to either the peplomeric S (gp200-gp100) or hemagglutinin HE (gp140-gp65) glycoproteins. BCV cDNA probes tested on purified viral preparations and coronavirus-positive (by electron microscopy) fecal samples from diarrheic turkey poults confirmed the relatedness of TCV and BCV. The two viruses produced distinct cytopathic changes in HRT-18 cells in the presence of trypsin, whereas only TCV isolates were able to reproduce the clinical symptoms in turkey poults. Their matrix (M) proteins undergo different glycosylation processes.

Detection of bovine enteric coronavirus in clinical specimens by hybridization with cDNA probes

Molecular hybridization, previously optimized for purified bovine coronavirus (BCV), was adapted for detection of virus in clinical specimens. For this purpose, the accuracy of the existing tests had to be improved and suitable means for removal of extraneous molecules had to be established. Six radioactive probes were used to obtain adequate detection signals. These probes, containing the complete N and E1 gene sequences and other sequences, hybridized to about 1/4 of the total length of the viral RNA. Genomic RNA could be detected after direct spotting of samples, but prior Freon-extraction or centrifugation of specimens on a cushion of sucrose improved considerably the positive identification of virus containing samples. RNA detection in positive clinical specimens was significantly better by hybridization than immunological detection of BCV by ELISA, although differences were slight after two passages of the virus on HRT-18 cell monolayers. Consequently, the reliability of positive and negative test results in hybridization tests on Freon extracted specimens was better than in ELISA. However, results after extraction with other organic solvents were inferior. The accuracy of ELISA was surpassed by hybridization assays. Background signals, due to vector homology were found to be negligible in all the samples analyzed.