Could recombinant technology facilitate the realisation of a fertility-control vaccine for possums?

While lethal control remains the primary tool for possum control in New Zealand, there has been substantial research effort over the last decade into controlling possum populations by reducing the animals' breeding potential. In particular, the potential of immunological control to reduce fertility has been investigated, whereby the possums' immune system is induced to react against its reproductive system, in order to block or destroy key components of the reproductive process. Two of the most targeted key components have been the blocking of circulating hormones (e. g. gonadotrophin-releasing hormone) and the inhibition of functional egg surface proteins (e. g. zona pellucida). While some success has been achieved for each approach, three main obstacles remain to the development of a working fertility-control vaccine for possums: first, ensuring that the vaccine remains efficacious in oral-delivery formulation; second, ensuring sufficient levels of fertility reduction; and third, ensuring that the induced immune response is sustained for a duration sufficient for long-term suppression of reproduction. The use of a genetically modified recombinant organism (parasite, bacterium or virus) to deliver a fertility-control vaccine could satisfy these requirements. A strong precedent for this approach has been set already in wildlife biology, namely the oral rabies vaccine, which is based on a recombinant vaccinia virus and which has been used successfully for the last 25 years as a disease-eliminating vaccine in mesocarnivores in Europe and North America. This review outlines the different forms and examples of recombinant organisms with potential for engineering into recombinant fertility-control vaccines to reduce possum reproduction; non-transmissible agents or fully-transmissible vectors are discussed, with shortcomings and benefits outlined for each.