Characterisation and monitoring of neutralisation-resistant VP2 phenotypes in BTV-1 isolates from northern Australia collected over a twenty-year period.

Phenotypic profiles of the VP2 protein of isolates of bluetongue virus serotype 1 (BTV-1) collected from Queensland and the Northern Territory, Australia, between 1979 and 1986 were analysed using neutralising monoclonal antibodies (MAbs) raised to the prototype isolate of Australian BTV-1 collected in the Northern Territory in 1979. Two distinct profiles were found. Northern Territory isolates exhibited the prototype profile, yet those from Queensland had a significantly different ('resistant') profile. Nucleotide sequencing of gene segment 2 from both groups of isolates was undertaken. When the nucleotide sequences of isolates from a later period in each State were analysed (1997-2001), all exhibited the 'resistant' profile. Thus, a novel VP2 phenotype, already in existence in Queensland, had supplanted a pre-existing VP2 phenotype in the Northern Territory between the two periods. Furthermore, amino acid differences between the resistant and prototype VP2 proteins were analogous to amino acid substitutions known to be associated with neutralisation resistance. The host immune response may therefore have contributed to selection of the 'resistant' phenotype.

Expression of the major inner capsid protein of the epizootic haemorrhagic disease virus in baculovirus and potential diagnostic use.

The RNA 7 encoding the major capsid protein (VP7) of epizootic haemorrhagic disease virus (EHDV), Australian serotype 2 (strain CS439), was cloned and the complete nucleotide sequence was determined. The coding region contained 1047 nucleotides (nt) capable of encoding a predicted 349 amino acid (aa) polypeptide with a calculated molecular size of 38.087 kDa. When the VP7 gene was expressed in bacterial or yeast expression systems, the expression product showed weak or no reactivity with polyclonal antibodies to EHDV. Therefore, the expression of the VP7 gene in baculovirus was pursued. The expressed EHDV VP7 was similar in antigenicity to that of the native virus as revealed by its reactivity in ELISA with monoclonal antibody (MAb) specific to EHDV. Preliminary ELISA results indicated that the recombinant protein binds to EHDV antibodies in serum and that these antibodies block the binding of EHDV-specific MAb. The availability of a reliable EHDV recombinant VP7 could enhance our existing assay for detection of EHDV-specific antibodies.