Vaccinia virus as a vaccine delivery system for marsupial wildlife

Vaccines based on recombinant poxviruses have proved successful in controlling diseases such as rabies and plague in wild eutherian mammals. They have also been trialled experimentally as delivery agents for fertility-control vaccines in rodents and foxes. In some countries, marsupial mammals represent a wildlife disease reservoir or a threat to conservation values but, as yet there has been no bespoke study of efficacy or immunogenicity of a poxvirus-based vaccine delivery system in a marsupial. Here, we report a study of the potential for vaccination using vaccinia virus in the Australian brushtail possum Trichosurus vulpecula, an introduced pest species in New Zealand. Parent-strain vaccinia virus (Lister) infected 8/8 possums following delivery of virus to the oral cavity and outer nares surfaces (oronasal immunisation), and persisted in the mucosal epithelium around the palatine tonsils for up to 2 weeks post-exposure. A recombinant vaccinia virus construct (VV399, which expresses the Eg95 antigen of the hydatid disease parasite Echinococcus granulosus) was shown to infect 10/15 possums after a single-dose oronasal delivery and to also persist. Both parent vaccinia virus and the VV399 construct virus induced peripheral blood lymphocyte reactivity against viral antigens in possums, first apparent at 4 weeks post-exposure and still detectable at 4 months post-exposure. Serum antibody reactivity to Eg95 was recorded in 7/8 possums which received a single dose of the VV399 construct and 7/7 animals which received triple-dose delivery, with titre end-points in the latter case exceeding 1/4000 dilution. This study demonstrates that vaccinia virus will readily infect possums via a delivery means used to deploy wildlife vaccines, and in doing is capable of generating immune reactivity against viral and heterologous antigens. This highlights the future potential of recombinant vaccinia virus as a vaccine delivery system in marsupial wildlife.