Claude Hamers

Persistently infected cattle stabilise bovine viral diarrhea virus leading to herd specific strains.

Animals persistently infected with BVDV are important in the epizootiology of the Bovine Viral Diarrhea (BVD) because they are a permanent source of contamination within a herd. These animals produce large quantities of virus and have, therefore, been proposed as responsible for generating antigenic variability. However, limited studies have failed to detect antigenic or genetic changes in viruses isolated at different time from persistently infected animals. One hypothesis to account for this stability is that the immunotolerance is accompanied by a selection against antigenic change. The presence of an immunotolerant persistently infected (IPI) animal in a herd would in turn lead to herd specific strains. To verify this hypothesis, we compared 17 BVDV strains isolated from IPI animals from 3 herds of Eastern Belgium. The comparison was based on the sequence of a 389 bp fragment of E2--a gene encoding for a highly variable glycoprotein. Sequences were strongly conserved within herds but were quite different between herds, indicating that BVDV herd-specific strains do exist and are associated with the presence of IPI animals.

Bovine viral diarrhoea virus induces apoptosis in blood mononuclear cells by a mechanism largely dependent on monocytes

The induction of apoptosis by bovine viral diarrhoea virus (BVDV) was examined in bovine peripheral blood mononuclear cells (PBMC) incubated with an antigenically homologous pair of non-cytopathic and cytopathic BVDV. Our results show that the cytopathic biotype, in contrast to the non-cytopathic counterpart, induces apoptosis in PBMC. Flow cytometry analysis of cells undergoing apoptosis revealed that: (1) monocytes constitute the major cell population undergoing apoptosis; (2) cytopathic virus also induces apoptosis in BoCD4+, BoCD8+ and BoWC1+ T cells in whole PBMC cultures but not in purified T cell suspensions; (3) the degree of apoptosis of BoCD4+ and BoCD8+ T cells incubated with the cytopathic virus was significantly enhanced by the presence of monocytes. Taken together, these results suggest that bovine monocytes play an important role in apoptosis induced by cytopathic BVDV.

Assessment of the clinical and virological protection provided by a commercial inactivated bovine viral diarrhoea virus genotype 1 vaccine against a BVDV genotype 2 challenge

A new genotype of bovine viral diarrhoea virus (BvDv), designated BVDV-2, has emerged in the last decade and in recent years the prevalence of BVDV-2 strains has increased. A vaccination-challenge study was carried out to determine the cross-protective efficacy of a commercial inactivated vaccine containing a BVDV-1 strain. A group of five BVDv-free calves was vaccinated twice and a second group of five calves served as negative controls. Two months after the first vaccination, all the calves were challenged intranasally with BVDV-2 strain BVD890. The clinical signs of disease, the changes in haematological variables and the level of viraemia were significantly less in the vaccinated group.