Contraceptive vaccines for wildlife: a review.

Wildlife, free-ranging and captive, poses and causes serious population problems not unlike those encountered with human overpopulation. Traditional lethal control programs, however, are not always legal, wise, safe, or publicly acceptable; thus, alternative approaches are necessary. Immunocontraception of free-ranging wildlife has reached the management level, with success across a large variety of species. Thus far, the immunocontraceptive research and management applications emphasis have been centered on porcine zona pellucida and gonadotropin-releasing hormone vaccines. Contraceptive success has been achieved in more than 85 different wildlife species, at the level of both the individual animal and the population. At the population management level with free-ranging species, the primary focus has been on wild horses, urban deer, bison, and African elephants. The challenges in the development and application of vaccine-based wildlife contraceptives are diverse and include differences in efficacy across species, safety of vaccines during pregnancy, the development of novel delivery systems for wild and wary free-ranging animals, and the constraints of certain non-contraceptive effects, such as effects on behavior. Beyond the constraints imposed by the public and a host of regulatory concerns, there exists a real limitation for funding of well-designed programs that apply this type of fertility control.

Contraceptive vaccines for the humane control of community cat populations.

Free-roaming unowned stray and feral cats exist throughout the world, creating concerns regarding their welfare as well as their impact on the environment and on public health. Millions of healthy cats are culled each year in an attempt to control their numbers. Surgical sterilization followed by return to the environment is an effective non-lethal population control method but is limited in scope because of expense and logistical impediments. Immunocontraception has the potential to be a more practical and cost-effective method of control. This is a review of current research in immunocontraception in domestic cats. Functional characteristics of an ideal immunocontraceptive for community cats would include a wide margin of safety for target animals and the environment, rapid onset and long duration of activity following a single treatment in males and females of all ages, and sex hormone inhibition. In addition, product characteristics should include stability and ease of use under field conditions, efficient manufacturing process, and low cost to the user. Two reproductive antigens, zona pellucida and GnRH, have been identified as possible targets for fertility control in cats. Zona pellucida, which is used successfully in multiple wildlife species, has achieved little success in cats. In contrast, immunization against GnRH has resulted in long-term contraception in both male and female cats following a single dose. GnRH is an ideal contraceptive target because it regulates pituitary and gonadal hormone responses in both males and females, thus suppressing nuisance behaviors associated with sex hormones in addition to preventing pregnancy. The responsiveness of cats to fertility control via GnRH suppression should encourage researchers and cat control stakeholders to continue efforts to optimize vaccines that induce multiyear contraception following a single dose in a high proportion of treated cats.

Implementing immunocontraception in free-ranging African elephants at Makalali conservancy.

The goal of programmes to provide contraception for elephants should be to formulate an approach that does not require the relocation or immobilisation of the same individual year after year, which would be long-lasting and cause minimal disruption to social and reproductive behaviour. The programmes should be simple to administer, safe and cost-effective, and must meet the objectives defined by managers in the field. An immunocontraceptive programme was initiated in a small free-roaming population of elephants at the Greater Makalali Private Game Reserve in Limpopo Province in 2000 to determine whether the porcine zona pellucida (pZP) vaccine can successfully control population sizes. Further objectives were to determine implementation costs and efficiency through a multi-faceted approach. We have demonstrated that immunocontraception meets the objectives set by managers in the field. Minimal social disruption was observed over the course of treatment, with the mode of delivery (ground or aerial vaccinations) determining the degree of stress within herds and speed of resumption of normal movement patterns. Aerial vaccinations resulted in the least disturbance, with target herds being approachable within a day. In 2005, implementation costs were R880-R1000/elephant/year, inclusive of darts, vaccine, helicopter and veterinary assistance. Irrespective of the source or method of vaccine delivery, a non-pregnant elephant is rendered infertile from 1st vaccine administration. The sooner immunocontraception is implemented, the sooner population growth rates can be controlled. pZP contraception is a realistic alternative management tool, particularly if used as part of a long-term management strategy. Mass-darting from the air eliminates the need for detailed individual histories of each elephant or for employing a person to monitor elephants. Thus, implementation of immunocontraception in larger populations is feasible and practical.

Comparative effects of GnRH and porcine zona pellucida (PZP) immunocontraceptive vaccines for controlling reproduction in white-tailed deer (Odocoileus virginianus).

Fawning rates and mating behaviour were compared between white-tailed deer (Odocoileus virginianus) treated with GnRH and porcine zona pellucida (PZP) immunocontraceptive vaccines from 1997 to 2000. Female deer from a herd of 102 deer at Seneca Army Depot, near Romulus, New York, were treated with prime and booster injections of PZP (n = 22) or GnRH vaccine (n = 32), or remained untreated as controls (n = 34). During the summers after booster treatment, observed fawning rates for adult female deer were similar for both PZP-treated (0.10-0.11 fawns per female) and GnRH-treated (0.13-0.22 fawns per female) female deer, and were significantly lower (t = -8.93 and t = -9.73; P < or = 0.0005, respectively) than those observed for control female deer (1.22-1.38 fawns per female). During the second (0.36 fawns per female) and third summers (0.61 fawns per female) after the last booster injection, GnRH-treated female deer still produced significantly fewer fawns than did the controls (1.38 and 1.31 fawns per female, respectively). In one breeding season after treatment, five of 18 (28%) females vaccinated with PZP produced fawns, similar to the rate for GnRH-treated females (29%). In addition, females treated with GnRH had fewer oestrous cycles per female (0.06, P < or = 0.05) than did either control (0.22 cycles per female) or PZP-treated deer (0.36 cycles per female). Initial PZP treatment followed by a booster dose 5-7 months later reduced fawn production and prolonged the breeding season as females repeatedly returned to oestrus, similar to results reported in other studies.

Virus-vectored immunocontraception of feral mammals.

The potential value of immunosterilization as a means to control species of wildlife that are widespread, numerous and undesirable is assessed. Key questions about the efficacy of fertility control and the means for delivering antigens expressed in recombinant viral vectors are discussed and the legal and social concerns that relate to its possible future use are raised.