Prolonged persistence of cytopathogenic bovine viral diarrhea virus (BVDV) in a persistently viremic cattle

Pathogenesis of primary respiratory disease induced by isolates from a new genetic cluster of bovine viral diarrhea virus type I

The pathogenesis of infection induced by cytopathogenic isolates from the newly identified genetic cluster Id of bovine viral diarrhea virus (BVDV) type I was studied in two experimental infections of previously seronegative, immunocompetent calves. Experiment 1 focused on the evaluation of clinical patterns, viremia, and serological responses. All infected calves in this experiment developed respiratory symptoms and seroconverted to BVDV positivity. Contact calves also contracted a respiratory tract infection following exposure to infected animals. Viremia was demonstrated between postinfection days 2 and 17, and the virus was detected in organ specimens of all but one each of the infected and contact calves. In experiment 2, the distribution of BVDV in various tissues of calves euthanized at defined days postinfection was studied. In two of these calves recurrent shedding of BVDV in nasal secretions was shown. BVDV was detected in various tissues of all infected calves throughout the experiment and also following seroconversion and the clearance of BVDV from the circulatory system. Despite the widespread distribution of the virus in various organs, significant tissue damage was found mainly in respiratory tract and lymphoid tissues. These experiments revealed that viruses from cluster Id of BVDV are able to induce primary respiratory disease in previously seronegative, immunocompetent calves. Contact transmission and virus recurrence, contrary to observations from acute experimental infections with noncytopathogenic BVDV, are likely to reflect differences in biological features of these cytopathogenic isolates. Virus shedding and its presence in tissues following peripheral clearance and in the presence of antibodies may have implications in the diagnosis, pathogenesis, and epidemiology of BVDV-induced syndromes in cattle.

A universal 'one-tube' RT-PCR protocol for amplifying isolates of bovine viral diarrhoea virus

The increase in the knowledge of the genetic variability of BVDV and the identification of some of the genetic determinants of its pathogenicity require robust and practical tools for rapid molecular characterization of the various genotypes of this virus. This study was undertaken to develop a standard protocol for RT-PCR that allows the amplification of various parts of the genome of BVDV without the need for optimizing each individual reaction. The reaction set-up is very flexible because it consists of two pre-mixes. These are a master mix, with all the required reagents except the desired primers, which are the components of the second pre-mix and are therefore easily interchangeable between the different reactions. After adding any primer-containing pre-mix to the fixed master mix, a non-interrupted cycling protocol led to the generation of amplicons of up to 4 kbp in size in amounts sufficient for subsequent sequencing reactions. The method was applied to five different regions of the BVDV genome: (i) the well-known 5'-UTR to differentiate genotypes I and II; (ii) the entire E2 gene, or an approximately 550 bp region within the E2 gene, in order to find the molecular equivalent of antigenic varieties; (iii) the entire structural protein coding region covering the Npro, capsid, ERNs, E1 and E2 genes: (iv) a 2.1 kbp region embracing the NS2/3 junction which is known to be cleaved in cytopathic biotypes of BVDV; and (v) the region covering the entire NS4B and NS5A/B genes. All six RT-PCRs were successfully applied using (i) primers with lengths of between 20 and 52 nucleotides, (ii) an aliquot of RNA extracted from either 10(6) infected bovine embryonal lung cells or the same number of leukocytes from viraemic cattle, and (iii) all the genotype I and II strains of BVDV tested. The technique described was used to generate various Sindbis virus/BVDV recombinants. The correct processing of the amplicon-derived E2 glycoprotein of BVDV strain PT810 was demonstrated by its reaction with a monoclonal antibody in an immunofluorescence assay. Given the variety of RT-PCRs tested, we conclude that this universal protocol may be useful with other RNA viruses.

Prolonged nasal shedding and viraemia of cytopathogenic bovine virus diarrhoea virus in experimental late-onset mucosal disease

A calf persistently infected with bovine virus diarrhoea virus (BVDV) was super-infected with a heterologous BVDV strain, C874, which contained non-cytopathogenic and cytopathogenic viruses. High titres of cytopathogenic BVDV were recovered in the three to four weeks after the challenge. Thereafter low titres of cytopathogenic virus were recovered repeatedly from the blood and the nose, with the titres in nasal secretions increasing in the four weeks before the onset of clinical signs. Neutralising antibodies against the challenge cytopathic virus (C874cp) were first detected 21 days after the super-infection, but these antibodies failed to neutralise the persisting non-cytopathogenic and cytopathogenic viruses isolated from the animal during the course of the infection. Serum collected from 105 days after the super-infection neutralised the cytopathogenic viruses isolated on day 105 and postmortem. These data indicate that unaltered wild-type C874cp was not directly responsible for the late-onset mucosal disease.

Experimentally induced "late-onset" mucosal disease--characterization of the cytopathogenic viruses isolated

Antigenic and genetic analyses were performed in order to establish relationships between the noncytopathogenic (ncp) and the cytopathogenic (cp) bovine viral diarrhoea viruses (BVDV) involved in the induction of a case of experimentally induced "late-onset" mucosal disease (MD) symptoms. The persistent ncpBVDV, the cpBVDV used for superinfection (strain TGAC) and the virus isolates from faeces (cpX) were examined using an immunoplaque test (IPT) to distinguish between cp and ncp virus populations. The cp populations were cloned by plaque purification and found to be free of ncpBVDV when using the IPT. The cpBVDV clones and the persistent ncpBVDV were analysed in an enzyme immunoassay on heat-fixed infected cells (IM-EIA) and in a neutralization test using a panel of 27 monoclonal antibodies against the E0 (gp48) and E2 (gp53) viral glycoproteins. It was found that strain TGAC contained two antigenically distinct subpopulations of cpBVDV (TGAC-B1 and TGAC-B2). The endogenous ncpBVDV and the cpX clones had the same reactivity pattern in both tests. In addition, p80 gene duplications in the genomes of the cpBVDV clones were analysed using the polymerase chain reaction and subsequent restriction enzyme analysis of the amplicons. The clones analysed from TGAC-B1 and those from cpX had gene duplications of identical sizes showing the same restriction enzyme patterns. Our results suggest that the cpBVDV which finally lead to "late-onset" MD arose by recombination and/or by mutations of the cpBVDV used for superinfection.