Bluetongue virus with mutated genome segment 10 to differentiate infected from vaccinated animals: a genetic DIVA approach.

Bluetongue virus (BTV) includes 24 serotypes and recently even more serotypes are proposed. Mass vaccination campaigns highlight the need for differential diagnostics in vaccinated populations. Bluetongue disease is routinely diagnosed by serological and virological tests by which differentiation infected from vaccinated animals (DIVA principle) is not possible. Real time PCR tests preferably detect all BTV serotypes (panBTV PCR tests). These PCR tests operate as frontline test to detect new BTV incursions. However, highly sensitive panBTV PCR tests can also detect currently applied inactivated and modified-live vaccines. Here, BTV with eight silent mutations in segment 10 (Seg-10) was generated by reverse genetics. This BTV mutant is not detected by a Seg-10 panBTV PCR test (genetic DIVA). Thus, inactivated BT vaccine with this mutated Seg-10 will avoid false positive PCR results post vaccination, whereas BTV infected animals can be positively diagnosed with the accompanying Seg-10 panBTV PCR test (DIVA-test) far beyond the infectious period.