A bait-delivered immunocontraceptive vaccine for the European red fox (Vulpes vulpes) by the year 2002?

An orally-delivered immunocontraceptive vaccine is being developed for the control of fox populations. A number of genes (PH-20, LDH-C4, ZP3) encoding gamete proteins have been cloned, produced in recombinant expression systems and used in fertility trials to test the efficacy of these antigens. As the immunocontraceptive vaccine will be delivered in a bait, there is a requirement for a greater understanding of the immune responses of the reproductive mucosa in canids, and the assessment of the best vaccine delivery system that will evoke a mucosal antibody response. Several vaccine delivery systems including microencapsulated antigens, and both vaccinia virus and bacterial vectors are being investigated. Oral administration of Salmonella typhimurium recombinants expressing different fox sperm antigens stimulates both systemic IgG responses to the antigen and a mucosal immune response within the female reproductive tract in the fox, indicating that salmonella may have potential with respect to the oral delivery of antigen. The enhancement of mucosal immune responses to orally-delivered vaccines is also being examined, research focussing on the possible use of fox-specific cytokines or the beta-subunit of cholera toxin in forming part of the vaccine construct.