Genetic stability in calves of a single strain of bluetongue virus.

Newborn calves were inoculated IV with highly plaque-purified bluetongue virus (BTV), serotype 10. The electrophoretic migration patterns of RNA segments and proteins of viruses isolated from calves at intervals after inoculation were compared. In addition, sera collected from calves at intervals after inoculation were compared for their abilities to neutralize several virus isolates from the same calf. Viremia persisted in calves for up to 56 days. Differences were not detected in the electrophoretic migration pattern of RNA segments or proteins of any of the BTV isolates. All calves produced high titers of neutralizing antibody to the original BTV inoculum by 28 days after inoculation, and significant (greater than or equal to 4-fold) differences were not detected in the neutralizing titers of sera to viruses collected at intervals after inoculation. The plaque-purified strain of BTV appeared to be stable genetically in infected calves, and failure to demonstrate antigenic variation among isolates indicated that antigenic shift was not the mechanism that allowed viremia to persist in BTV-infected calves.