IMMUNOCONTRACEPTION IN RODENTS - A REVIEW OF THE DEVELOPMENT OF A SPERM-BASED IMMUNOCONTRACEPTIVE VACCINE FOR THE GREY SQUIRREL (SCIURUS-CAROLINENSIS)

The strategy for developing contraceptive vaccines for wild rodents wi ll depend on the species. In rats and mice, high all-year birth rates, high levels of dispersal and promiscuous mating systems suggest that, if immunocontraception was used alone, >90% of the population would h ave to sterilized to achieve the desired control. In Britain, the grey squirrel (Sciurus carolinensis) may be a better candidate to investig ate the feasibility of a contraceptive vaccine in rodents. This introd uced species is a seasonal breeder with a much lower population turnov er than rats or mice. As well as causing damage to woodland, it has ou sted the native red squirrel (S. valgaris) from most of the UK. A huma ne and selective method for the control of grey squirrels is therefore highly desirable. Numerous sperm-specific antigens have been identifi ed on rodent spermatozoa. Monoclonal antibodies to particular componen ts block sperm-egg interactions in laboratory animals and cross-react with grey squirrel spermatozoa. In vitro fertilization assays indicate that squirrel sperm-egg binding may be inhibited also. Currently, a c DNA library obtained from grey squirrel testis is being screened to id entify genes encoding specific sperm antigens involved in fertilizatio n. Methods of enhancing immunogenicity after oral immunization using m icroparticle carriers and immune-stimulating complexes are currently u nder investigation.