Bluetongue Disabled Infectious Single Animal (DISA) vaccine: Studies on the optimal route and dose in sheep.

Bluetongue (BT) is a disease of ruminants caused by bluetongue virus (BTV) transmitted by biting midges of the Culicoides genus. Outbreaks have been controlled successfully by vaccination, however, currently available BT vaccines have several shortcomings. Recently, we have developed BT Disabled Infectious Single Animal (DISA) vaccines based on live-attenuated BTV without expression of dispensable non-structural NS3/NS3a protein. DISA vaccines are non-pathogenic replicating vaccines, do not cause viremia, enable DIVA and are highly protective. NS3/NS3a protein is involved in virus release, cytopathogenic effect and suppression of Interferon-I induction, suggesting that the vaccination route can be of importance. A standardized dose of DISA vaccine for serotype 8 has successfully been tested by subcutaneous vaccination. We show that 10 and 100times dilutions of this previously tested dose did not reduce the VP7 humoral response. Further, the vaccination route of DISA vaccine strongly determined the induction of VP7 directed antibodies (Abs). Intravenous vaccination induced high and prolonged humoral response but is not practical in field situations. VP7 seroconversion was stronger by intramuscular vaccination than by subcutaneous vaccination. For both vaccination routes and for two different DISA vaccine backbones, IgM Abs were rapidly induced but declined after 14days post vaccination (dpv), whereas the IgG response was slower. Interestingly, intramuscular vaccination resulted in an initial peak followed by a decline up to 21dpv and then increased again. This second increase is a steady and continuous increase of IgG Abs. These results indicate that intramuscular vaccination is the optimal route. The protective dose of DISA vaccine has not been determined yet, but it is expected to be significantly lower than of currently used BT vaccines. Therefore, in addition to the advantages of improved safety and DIVA compatibility, the novel DISA vaccines will be cost-competitive to commercially available live attenuated and inactivated vaccines for Bluetongue.