Seven cytopathic isolates of bovine viral diarrhea virus (BVDV) isolated from clinical cases and blood of calves from herds with reproductive problems were analysed. All isolates contained a mixture of cytopathic (cp) and noncytopathic (ncp) viruses which were biologically cloned yielding pure populations of viruses of either biotype. The cp and ncp viruses obtained by cloning were characterized antigenically with a panel of monoclonal antibodies (MAbs) and regarding to the expression of the non-structural polypeptide NS3. The analysis of MAb binding revealed two patterns of reactivity: 1. In five isolates, the cp and ncp viruses from the same isolate were antigenically very similar to each other, suggesting they represent true "pairs"of viruses. 2. Two isolates, however, yielded cp and ncp viruses antigenically different from each other. Western immunoblot analysis of non-structural polypeptides of ncp viruses revealed a unique band of reactivity, with a mass of approximately 125kDa, corresponding to the NS23 of the standard BVDV Singer strain. In addition to NS23, the cp viruses expressed a polypeptide of approximatelly 80kDa, corresponding to the NS3. The NS23 of two cp viruses displayed an altered migration in SDS-PAGE compared to the other viruses. In one virus, the NS23 had a molecular mass lower than expected whereas in other virus, two bands of reactivity were observed: one smaller and another bigger than the standard NS23, respectively. Our findings confirm previous results that cytopathic BVDV field isolates usually contain a mixture of viruses of both biotypes and that cytopathogenicity correlates with the expression of NS3. The isolation of cp viruses from the blood of clinically normal cattle, however, demonstrates that their occurrence is not restricted to cases of mucosal disease.
bovine viral diarrhea virus; BVDV; antigenic diversity; cytopathology
