Antigenic and immunogenic characterisation of avian reoviruses

The antigenic relationship of 9 avian reoviruses of Australian origin was investigated by comparing the protein migration patterns of immunoprecipitated isotopically-labelled infected cell lysates in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDSPAGE). Close agreement with previously reported neutralisation test results and the precipitation of the σC protein was obtained. The results suggested that the σC protein was the major neutralisation protein, that it confers type-specificity to avian reoviruses, and is analogous to the g σ1 protein of mammalian reoviruses. Nine selected avian reovirus isolates were assigned to 4 antigenic groups based upon precipitation of the σC protein. Reassortants were produced between the parent viruses with the ability to replicate in Vero cells and those that were unable to replicate in Vero cells. Of the 9 reassortants examined, 8 were able to grow in Vero cells. Two gene segments, M2 and SI always originated from the parent virus (RAM-1) able to grow in Vero cells and never from the parent virus unable to grow in Vero cells. These results suggested that either the M2 or the SI gene segments were associated with the ability of the reassortant viruses to replicate in Vero cells, although 4 other gene segments in all the parent reoviruses used exhibited a similar migration rate during SDS-PAGE and their possible role in the replication of virus in Vero cells could not be determined. Temperature-sensitive (ts) mutants of the Vero cell-adapted RAM-1 strain of avian reovirus were induced for use as potential vaccine strains in Australia. During these experiments it was also determined that the parent RAM-1 strain already possessed ts characteristics. The virulence of one of the ts mutant (P20) selected for further study was compared to the parent virus and 2 other strains of avian reovirus. It was determined that both the parent RAM-1 virus and the ts mutant P20 had lower virulence for chickens than the 2 other strains of reovirus examined (724 and 1091) and that the virulence was dose-dependent. Multiple immunisation of chickens with the RAM-1 strain of virus resulted in the production of high titres of neutralising antibody to the homologous virus and to 2 other antigenically heterologous viruses (724 and 1091) with the passive transfer of these antibodies to progeny chickens via the egg yolk. Challenge experiments using high titred virus to induce tenosynovitis lesions showed that progeny chickens from hens immunised with the RAM-1 strain were protected against challenge with the homologous RAM-1 strain, were partially protected against challenge with the heterologous virus strain 724 but were not protected against challenge with the virus strain 1091. The results indicated that protection against avian reovirus infection in Australia would probably require the use of a polyvalent vaccine, and that selection of the appropriate vaccine strain should be based upon identification of the type-specific σC protein in isolates associated with disease