Antigenic differences among pestiviruses

Virus-like particles of chimeric recombinant porcine circovirus type 2 as antigen vehicle carrying foreign epitopes

Virus-like particles (VLPs) of chimeric porcine circovirus type 2 (PCV2) were generated by replacing the nuclear localization signal (NLS; at 1–39 aa) of PCV2 capsid protein (Cap) with classical swine fever virus (CSFV) T-cell epitope (1446–1460 aa), CSFV B-cell epitope (693–716 aa) and CSFV T-cell epitope conjugated with B-cell epitope. The recombinant proteins were expressed using the baculovirus expression system and detected by immunoblotting and indirect immunofluorescence assay. The abilities to form PCV2 VLPs were confirmed by transmission electron microscopy. Immunogenicities of the three recombinant proteins were evaluated in mice. Our Results indicated that Cap protein NLS deletion or substitution with CSFV epitopes did not affect the VLPs assembly. Three chimeric Cap proteins could form VLPs and induce efficient humoral and cellular immunity against PCV2 and CSFV in mice. Results show that PCV2 VLPs can be used as an efficient antigen carrier for delivery of foreign epitopes, and a potential novel vaccine.

Recombinant pestivirus E2 glycoproteins prevent viral attachment to permissive and non permissive cells with different efficiency

Bovine viral diarrhoea virus (BVDV) is an economically important animal pathogen, which like other pestiviruses has similar molecular biological features to hepaciviruses, including human Hepatitis C virus. The pestivirus E2 glycoproteins are the major target for virus-neutralising antibodies, as well as playing a role in receptor binding and host range restriction. In this study, recombinant E2 glycoproteins (rE2) derived from three different pestivirus species were examined for their inhibitory effects on pestivirus infectivity in cell culture. Histidine-tagged rE2 glycoproteins of BVDV type 2 strain 178003, BVDV type 1 strain Oregon C24V and CSFV strain Alfort 187 were produced in Spodoptera frugiperda insect cells and purified under native conditions. The ability of rE2 glycoprotein to inhibit the infection of permissive cells by both homologous and heterologous virus was compared, revealing that the inhibitory effects of rE2 glycoproteins correlated with the predicted similarity of the E2 structures in the recombinant protein and the test virus. This result suggests that the sequence and structure of E2 are likely to be involved in the host specificity of pestiviruses at their point of uptake into cells.

Practical significance of heterogeneity among BVDV strains: Impact of biotype and genotype on U.S. control programs

In the early 1990s research groups in North America noted that a newly recognized severe acute form of bovine viral diarrhea virus infection, referred to as hemorrhagic syndrome or severe acute BVDV (SA BVDV), was associated with a genetically distinct subgroup of BVDV strains. This new subgroup was named BVDV genotype 2 or BVDV2. All BVDV strains previously characterized in the literature belonged to a separate genotype, BVDV1. However, not all strains identified as BVDV2 were associated with severe acute infections. If I did this deletion, I did not mean to do it. I think it was already here, though. I see there are some other big edits that I did not do; fine. Hollis subsequent surveys of BVDV strains isolated from clinical submissions to diagnostic laboratories and contaminated fetal calf serum suggested that the ratio of BVDV2 to BVDV1 strains in the U.S. approached 50%. Further, while antigenic cross reactivity is seen between BVDV1 and BVDV2 strains, a log or more difference is typically observed in titers against viruses from different genotypes. These observations prompted vaccine manufacturers in North America to produce vaccines against BVDV that contained antigens from both BVDV1 and BVDV2 strains. Under experimental conditions, these new vaccines offered improved protection against type 2 strains, however field data are still insufficient to assess their efficacy in practice. The BVDV genotypes may also be segregated into subgenotypes. Two subgenotypes of both BVDV1 (BVDV1a and BVDV1b) and BVDV2 (BVDV2a and BVDV2b) have been reported in North American. BVDV2a predominates with BVDV2b isolation a rare event. In contrast, BVDV1a and BVDV1b are both commonly isolated. Antigenic differences observed between strains from the BVDV1a and BVDV1b subgenotypes have led to the suggestion that protection may be improved by inclusion of strains from both BVDV1a and BVDV1b in vaccines in addition to BVDV2. The cost to benefit ratio of this proposal is currently a matter of debate.

Virus neutralising antibodies against 22 bovine viral diarrhoea virus isolates in vaccinated calves

Seven of nine colostrum deprived calves, free from bovine viral diarrhoea virus (BVDV), were vaccinated with a commercially available vaccine containing two inactivated strains of BVDV, an inactivated strain of bovine herpesvirus-1 and modified-live strains of bovine respiratory syncytial virus and para-influenza-3 virus. The two other calves were kept as controls. The virus neutralising (VN) antibodies induced by vaccination were tested against 22 antigenically diverse BVDV isolates, including reference strains and field isolates, both cytopathic and non-cytopathic, as well as genotypes I and II. The strains were isolated in Belgium, France, Germany, the United Kingdom and the USA. While there were variations in the VN titres of the individual calves against all the strains, serum from the seven animals neutralised 20 or more of the strains tested. From the results, it can be concluded that the vaccine can stimulate the production of VN antibodies capable of neutralising a wide range of European and American isolates of BVDV, including genotypes I and II.

Diversity among bovine pestiviruses

Bovine viral diarrhoea virus (BVDV) isolates are characterized by an important genetic, antigenic and pathogenic diversity. The emergence of new hypervirulent BVDV strains in North America has provided clear evidence of pathogenic differences between BVDV strains. The origin of BVDV diversity is related to high mutation rate occurring in RNA viruses but the consequences of mutations obviously depend on the genes which are involved. Mutations in genes encoding for structural proteins of immunological importance may have practical implications. Knowledge of BVDV diversity is important for understanding the wide variety of pathogenesis of diseases caused by the virus, for monitoring the epidemiology of the different types and for the design of optimum laboratory tests and vaccines. This review focuses on the origin and consequences of BVDV diversity with regard to pathogenesis, biotypes, and antigenic and genetic variations.

Persistent bovine pestivirus infection localized in the testes of an immuno-competent, non-viraemic bull

A post-pubertal bull on an artificial insemination station was found to be persistently shedding bovine viral diarrhoea virus (BVDV) in semen over a period of eleven months, while demonstrating no viraemia. Circulating antibodies to BVDV were consistently high, suggesting that the immune system was challenged repeatedly. Post-mortem findings confirmed that the virus was sequestered in the testes of the bull. It is hypothesized that the BVDV in this immuno-competent bull was protected from the bull's immune response by the blood-testes barrier. The barrier becomes functional only at puberty when tight junctions form between adjacent Sertoli cells, suggesting that this bull became persistently infected with BVDV during puberty.