In this two-part series on wildlife immunocontraception, AWI discusses the practicalities and politics behind this emerging humane technology. In the first article (AWI Quarterly, Fall 2011), AWI provided background information about immunocontraception with a focus on its use as an alternative to lethal control of white-tailed deer. In this article, AWI compares two leading vaccines, explores successful immunocontraceptive field studies, and examines the politics that continue to hinder the development and application of immunocontraceptive vaccines.
In part one of this series, AWI looked at two immunocontraceptive vaccines used to humanely control reproduction in captive and suburban wildlife populations: porcine zona pellucida (PZP), a natural vaccine produced by the Science and Conservation Center based in Billings, Montana, and GonaConTM, a synthetic vaccine developed by scientists affiliated with the National Wildlife Research Center of the USDA's Animal and Plant Health Inspection Service. Although PZP has been remarkably successful in controlling reproduction in a multitude of species, including white-tailed deer and wild horses, the USDA has spent substantial funds on the study of GonaConTM as an alternative. The “competition” to determine who can develop the more effective and longlasting vaccines has likely benefitted both research camps, and both vaccines show promise as a method for non-lethal control of suburban wildlife populations.
To briefly compare the two vaccines: While both PZP and GonaConTM cost very little per dose, GonaConTM is synthetic and simpler to manufacture (logistically, practically, and from a regulatory standpoint) than PZP, which is produced from a natural product. However, GonaConTM is more expensive and less practical to apply since it generally requires the capture of the target animals, while PZP can be delivered remotely through darts and bio-bullets. GonaConTM, when used on captive animals, has demonstrated a multi-year level of efficacy based on a single-shot of the vaccine. However, when tested in the wild, the efficacy of GonaConTM declines substantially. Although PZP as a single, two-shot treatment has increased efficacy over time compared to GonaConTM, to retain its effectiveness on a long-term basis, animals currently have to be “boosted” annually, which adds to the time, costs and logistical difficulties of administering PZP.
In response to such difficulties, technologies for longer-lasting single-shot vaccines have emerged, and both PZP and GonaConTM have been altered to boost the duration of effectiveness in wild horse and white-tailed deer populations. Scientists - including those at the Science and Conservation Center, Allen Rutberg of Tufts University’s Cummings School of Veterinary Medicine, and John Turner at the Toledo University School of Medicine - have had particular success employing the PZP vaccine to control white-tailed deer populations at several study sites.
Perhaps the most successful demonstration of the value of PZP in deer management has occurred at Fire Island National Seashore (FIIS) in New York. The National Park Service (NPS) conducted a deer fertility control project on Fire Island from 1993 to 2010. The birth of fawns on the island fell dramatically within the first few years of PZP use, with several hundred deer treated each year. Efforts focused on deer living in densely populated urban areas where, in time, the deer population decreased by nearly 70 percent.
The published results demonstrate that PZP is highly effective in inhibiting fertility, reversible, safe to use in pregnant animals, has no significant short- or long-term health effects, and does not pass through the food chain - all important criteria for an effective and acceptable fertility control agent. Furthermore, the ability to deliver PZP remotely without capturing and tagging animals makes PZP an easy-to-use and humane immunocontraceptive agent.
Field projects elsewhere have shown similar reductions, with fertility reduced by 72 to 86 percent. On Fripp Island, South Carolina, for example, the deer population was halved—from 2005 to 2010. Not surprisingly, the health of individual deer improved as deer density declined and remaining deer had access to more forage, while females avoided the rigors and physiological costs of reproduction.
In the fall of 2010, however, the NPS suddenly terminated the immunocontraception program on Fire Island. Eventually, FIIS Superintendent K. Chris Stoller claimed that halting the use of immunocontraception was necessary to transition from a “research project” to a white-tailed deer “management plan.” Developing this plan will entail consideration of other alternatives, presumably including lethal control, to manage the island’s white-tailed deer - a population that had been successfully controlled using immunocontraception for nearly two decades. Indeed, by terminating this project, the NPS appears to be undermining the benefits achieved through immunocontraception research, in that the deer population will be allowed to resume unchecked growth while the management plan is developed. Why did the NPS not allow the immunocontraception project to continue at FIIS while it prepared a management plan? Is there an assumption from a legal standpoint that research and management must be mutually exclusive?
This is not the only example of a PZP success story being abruptly cut short without explanation. The Fripp Island project and the Metro Parks project in Columbus, Ohio (1995–2003), were both terminated by state wildlife agencies concerned that the projects were becoming more about “management” and less about “research.” The Fripp Island project was originally supported by the South Carolina Department of Natural Resources before it terminated the effort, and the department has reported that it may still consider the use of GonaConTM on the island.
The sudden halt of these successful projects is likely the result of vehement political opposition that still exists in some quarters to the use of immunocontraceptives for wildlife. State wildlife agencies, as well as hunters and allied organizations, see deer contraception as a threat to the tradition and culture of hunting (or the revenue generated by hunting), even though it has only been proposed for use on deer populations unable to be efficiently or safely controlled through hunting. There is also trepidation about trying new management techniques that do not coincide with the way things have always been done. Simply put, as the old saying goes, “it is tough to teach an old dog new tricks.” Indeed, many of these agencies and organizations have engaged in a campaign of obstruction, misinformation, and outright deception to derail the development, expansion and field validation of immunocontraception. Sadly, such efforts have slowed the testing of deer immunocontraceptive agents in urban and suburban areas dramatically.
Given the culture, politics, and economics involved, it is of little surprise that this controversy seems to be confined to deer management. Based on published research, the use of PZP is steadily increasing in wild and domestic horses, zoo animals, bison (domestic and wild) and elephants. Last year the number of zoo animals successfully treated with PZP to limit reproduction doubled. In reference to wild horses, sanctuaries, tribes, and the Bureau of Land Management are all expanding their use of PZP to control fertility. Expressing a viewpoint that is perhaps shared by many others, one scientist quipped, “states are open to using contraception on species like pigeons until that same contraception is proposed for a ‘game’ animal, like geese, because it could threaten the sale of hunting licenses.”
For now, deer contraception research projects are largely moving forward on federal land where state wildlife agencies have limited authority. However, as touched on above, federal agencies such as the NPS are also obstructing the use of this humane technology and purposefully creating stringent wildlife contraception criteria to deter the immediate application of immunocontraception. In its place, the NPS has allowed sharpshooters - under cover of darkness, using nightvision equipment and weapons equipped with silencers—to invade our parks and mercilessly slaughter deer attracted to artificial bait piles.
Despite such tactics, there remains a public demand for an effective, efficient, and low-cost immunocontraceptive agent. With a burgeoning human population, wildlife and wildlife habitat are being lost at an accelerating pace. As humans continue to spread over the landscape, they are increasingly coming into conflict with wildlife. While, in an ideal world, people would respect and enjoy wildlife and allow natural factors to control their abundance, lethal control of wildlife is the current reality. Immunocontraception is a tool that can be used to alter this reality—to resolve conflicts while avoiding the cruelty of lethal control. Indeed, as societal norms and values change to embrace humane wildlife management, those stuck in the past should take note of a science-powered alternative coming their way.