Monoclonal antibodies (MAbs) were produced against the G, M2 and N proteins of bovine ephemeral fever virus (BEFV) and 29 were selected for further study. Thirteen neutralizing MAbs were assigned to one conformation-independent and at least two conformation-dependent antigenic sites on the G protein by a competitive binding ELISA. The panel of MAbs were tested by neutralization and immunofluorescence with three strains of BEFV and three BEFV-related viruses. The results indicated that BEFV strains from different sources were not identical and that the M2 protein was the least variable of the proteins investigated. Passive protection studies in mice showed that the correlation between neutralizing titre and resistance to challenge was 0-85 (P < 0.001).

Antigenic variation in the bovine ephemeral fever virus glycoprotein was demonstrated using monoclonal antibodies and comparing a particular passage level of the BB7721 strain with (1) other Australian isolates of BEF virus, (2) the Beijing 1 strain of BEF virus, isolated in China and (3) batches of the BB7721 strain with different passage histories. Escape mutants of BEF virus were selected from cell culture and suckling mice, by growing virus in the presence of neutralising monoclonal antibodies. Escape frequencies were calculated for 14 monoclonal antibodies and an epitope map constructed of antigenic sites on the BEF viral glycoprotein which induce the production of neutralising antibodies.

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