Abstract:
The strategy for developing contraceptive vaccines for wild rodents willdepend on the species. In rats and mice, high all-year birth rates, highlevels of dispersal and promiscous mating systems suggest that, ifimmunocontraception was used alone, >90% of the population wouldhave to sterilized to achieve the desired control. In Britain, the greysquirrel (Sciurus carolinensis) may be a bettercandidate to investigate the feasibility of a contraceptive vaccine inrodents. This introduced species is a seasonal breeder with a much lowerpopulation turnover than rats or mice. As well as causing damage to woodland,it has ousted the native red squirrel (S. valgaris) frommost of the UK. A humane and selective method for the control of greysquirrels is therefore highly desirableNumerous sperm-specific antigens have been identified on rodent spermatozoa.Monoclonal antibodies to particular components block sperm-egginteractions in laboratory animals and cross-react with grey squirrelspermatozoa. In vitro fertilization assays indicate thatsquirrel sperm-egg binding may be inhibited also. Currently, a cDNAlibrary obtained from grey squirrel testis is being screened to identify genesencoding specific sperm antigens involved in fertilization. Methods ofenhancing immunogenicity after oral immunization using microparticle carriersand immune-stimulating complexes are currently under investigation.