- Volume 82, Issue 11, 2001

Ovine herpesvirus-2 (OHV-2) infection has been associated with malignant catarrhal fever (MCF) in susceptible ruminants. In order to further investigate whether OHV-2 is an aetiological agent for sheep-associated (SA) MCF in cattle and bison, the entire sequences of OHV-2 glycoprotein B (gB) from different sources of viral DNA were compared. Target DNA was derived from tissues of bovine and bison cases of SA-MCF, from a lymphoblastoid cell line established from another bovine case of SA-MCF, and from a healthy sheep. The divergence between deduced amino acid sequences of OHV-2 gB ranged from 0·5 to 1·2%. The high degree of similarity between gB sequences from a healthy sheep and clinical cases of SA-MCF in cattle and bison suggests that OHV-2 is an ovine virus that is occasionally transmitted to other ruminant species, in which it can cause severe disease.

Murine polyomavirus VP1 virus-like particles (VLPs) can bind plasmid DNA and transport it into cells both in vitro and in vivo. Long-term expression of the transgene can be observed, suggesting that VP1 VLPs may be used as DNA delivery vehicles for gene therapy. In this study we have analysed the in vitro efficiency of transfection using different DNA/VLP molar ratios and the immune response induced following intranasal administration of these complexes to mice. Our results indicate that in short-term in vitro culture VP1 VLP–DNA complexes appear to be as efficient as DNA alone at transfecting cell monolayers. They also show that VP1 VLPs are very immunogenic, inducing high proliferative cell responses and both serum and mucosal antibodies. Moreover, VP1 VLP–DNA complexes appear to be capable of inducing a stronger immune response to the transgene product (β-galactosidase) than immunization with DNA only. The results suggest that polyomavirus VP1 VLPs derived from the wild-type sequence may be too immunogenic for repeated use as gene delivery vehicles in gene therapy. However, due to their high immunogenicity and apparent adjuvant properties, they could be modified and used as vaccines either on their own or complexed with DNA.

Neutralization capsid epitopes are important determinants for antibody-mediated immune protection against papillomavirus (PV) infection and induced disease. Chimeric L1 major capsid proteins of the human PV type 16 (HPV-16) and the bovine PV type 1 (BPV-1) with a foreign peptide incorporated into several capsid surface loops self-assembled into pentamers or virus-like particles (VLP). Binding patterns of neutralizing monoclonal antibodies (MAb) and immunization of mice confirmed (i) that regions around aa 282–286 and 351–355 contribute to neutralization epitopes and identified the latter region as an immunodominant site and (ii) that placing a foreign peptide in the context of an assembled structure markedly enhanced its immunogenicity. Pentamers disassembled from wild-type HPV-16 and BPV-1 VLPs displayed some of the neutralization epitopes that were detected on fully assembled VLPs, but were deficient for binding a subset of neutralizing MAb that inhibit cell attachment.

The circular, single-stranded DNA genome of a novel circovirus of canaries, tentatively named canary circovirus (CaCV), was cloned and sequenced. Sequence analysis indicated that the genome was 1952 nucleotides (nt) in size and had the potential to encode three viral proteins, including the putative capsid and replication-associated (Rep) proteins. The CaCV genome shared greatest sequence similarity (58·3% nt identity) with the newly characterized columbid circovirus (CoCV) and was more distantly related to the two porcine circovirus strains, PCV1 and PCV2, beak and feather disease virus (BFDV) and a recently isolated goose circovirus (GCV) isolate (46·8–50·9% nt identity). In common with other members of the Circovirus genus, several nt structures and amino acid motifs thought to be implicated in virus replication were identified on the putative viral strand. Phylogenetic analysis of both the capsid and Rep protein-coding regions provided further evidence that CaCV is more closely related to CoCV and BFDV and more distantly related to GCV, PCV1 and PCV2.

Bombyx mori densovirus (BmDNV-1), on the basis of the previously reported genome sequence, constitutes by itself a separate genus (Iteravirus) within the Densovirinae subfamily of parvoviruses. Inconsistencies in the genome organization, however, necessitated its reassessment. The genome sequence of new clones was determined and resulted in a completely different genome organization. The corrected sequence also contained conserved sequence motifs found in other parvoviruses. Some amino acids in the highly conserved domain in the unique region of VP1 were shared by critical amino acids in the catalytic site and Ca2+-binding loop of secreted phospholipase A2, such as from snake and bee venoms. Expression of this domain and determination of enzyme activity demonstrated that capsids have a phospholipase A2 activity thus far unknown to occur in viruses. This viral phospholipase A2, which is required shortly after entry into the cell, showed a substrate preference for phosphatidylethanolamine and phosphatidylcholine over phosphatidylinositol.