VP2 Virus-Like Particles elicit protective immunity against 1 duckling short beak and dwarfism syndrome in duck and chicks

17 Duckling short beak and dwarfism syndrome virus (SBDSV), an emerging goose 18 parvovirus, that has caused serious outbreaks of short beaks and dwarfism syndrome 19 (SBDS) in Chinese duck flocks since 2015. Presently, there is no commercial vaccine 20 against SBDS. In the present study, a virus-like particle (VLP) based candidate 21 vaccine was developed against this disease. A baculovirus expression system was used 22 to efficiently express the SBDSV VP2 protein in Sf9 cells. Immunofluorescence assay, 23 SDS-PAGE, and Western blot were used to confirm protein expression. Furthermore, 24 transmission electron microscopy was used to observe the formation of VLPs. Finally, 25 VLPs were formulated in an oil-adjuvanted vaccine to evaluate humoral responses in 26 ducks and chicks via latex particle agglutination inhibition assay (LAI) and 27 microneutralization assay. A single injection with this oil-adjuvanted VLP vaccine 28 induced high levels of LAI and neutralization antibodies in ducks and chickens, with 29 LAI peak titer as 4.9 ± 1.20, 4.4