Joint treatment with azidothymidine and antiserum for eradication of avian leukosis virus subgroup a contamination in vaccine virus seeds.

Contamination of avian attenuated vaccines by avian leukosis virus (ALV) is considered to be a specific horizontal transmission of ALV. Eradication of ALV contamination in vaccine virus seeds is thus a precondition of qualified vaccine production. In this study, we used the nucleoside reverse transcriptase (RT) inhibitor azidothymidine (AZT) together with monofactor antiserum against avian leukosis virus subgroup A (ALV-A) to remove ALV-A from vaccine virus seeds. Different doses of ALV-A were artificially added to the Newcastle disease virus (NDV) vaccine seeds, then the ALV-contaminated attenuated virus vaccine virus seeds were cultured in DF-1 cells. Single-drug treatment with 5 μg/mL AZT or 5% (v/v) as well as combined treatment with AZT and antiserum significantly suppressed ALV-A replication (P < 0.001) in the vaccine virus seeds. Complete absence of virus replication was observed in cells exposed to joint treatment with AZT and antiserum. The treated virus seeds met the requirements of the Chinese Ministry of Agriculture. Therefore, combined treatment with AZT and antiserum can be used to eradicate contaminating ALV-A from vaccine virus seeds, thus providing a new approach for improving vaccine safety.