Differential serologic responses to reassortant bluetongue viruses recovered from a bull.

Although the simultaneous infection of individual animals with more than one serotype of bluetongue (BLU) virus has been documented, the humoral immune responses elicited by viral reassortants recovered from the host has not been reported. This study characterized the serologic responses of a bull infected with BLU serotypes 11 and 17. Genome reassortants isolated from this bull over the course of 34 days were used. The genomic profiles of the reassortants were characterized by polyacrylamide gel electrophoresis of viral double stranded RNA under reducing conditions using two concentrations of acrylamide. This approach permitted the detection of three novel genome segments among the isolates. Selected reassortants were tested in plaque neutralization assays, using serum samples collected from the bull at different times during the infection. To better define the role of BLU virus outer capsid proteins in viral antigenicity, the neutralizing antibody titer curves of viral isolates that contained reassorted VP2 and VP5 were compared to those of the parental strains and of other reassortants. The present study reports the heterotypic pattern of neutralization of the bull sera against different reassortants recovered from this animal.