On wildlife birth control, “rut without risk,” immunocontraception, transgenic plants and viruses, modulated hormones, bioweapons, Jurassic Park, and the promise of sterile mosquitoes

by Janet A. Ginsburg

It probably didn’t help that we were traveling with a National Wildlife Federation biologist. NWF had long been on record opposing several predator control methods favored by Wildlife Services, including aerial shooting, the use of cyanide-bated M-44 “land mines”, and “livestock protection collars” (sheep collars loaded with a packets of Compound 1080, a Nazi–era poison so deadly, a fraction of a gram can kill a man -- presumably, any predator foolish enough to attack a sheep wearing a collar would swallow a lethal dose along with its final meal. (For more, read sidebar: ”They Shoot (Trap and Poison) Coyotes, Don’t They?”)

That particular day, though, we were there to talk about a very different type to predator control: contraception. Hailed as a more humane approach, wildlife birth control was generating considerable buzz, and ground zero for research was out in the middle of beautiful nowhere Utah, where dosage and delivery options were being tested on dozens of coyotes caged in a warren of grid-perfect pens. It didn’t take long to figure out that a seemingly elegant solution on paper would have to negotiate some serious hurdles out in the wild: There was simply no way to make sure that only coyotes of the right sex and age would get the right dose at the right time.

Ten years and millions of research-dollars later, they still haven’t figured it out. But the field of wildlife birth control is nonetheless booming, driven in part by an invasion of deer, geese and coyotes into the hunting-free heart of ever-sprawling suburbia. And beyond all the neatly-trimmed hedges, contraception is also becoming the popular choice for a whole Noah’s ark-worth of species: elephants, possums, kangaroos, horses, bison, cats, fish, even mosquitoes. Hormones are modulated, immune responses manipulated, and DNA obliterated. Delivery is equally cunning, ranging from dart, “bio-bullet” (a drug-laced plastic bullet) and bait, to transgenic plants and viruses.

Still, what are the options? There are now so many deer that deer / auto collisions have become a billion-dollar-plus problem in the U.S, while once-rare Canada geese have taken over parks, golf courses, and even the occasional parking lot, leaving trails of distinctive pellets wherever they waddle (4 pounds per day per bird…) Clearly, something needs to be done.

Here then is a Contraception Sampler:

PZP / Immunocontraception: This is a vaccine designed to trigger an immune response preventing fertilization. The zona pellucida (ZP) is a membrane found on all mammalian eggs. The vaccine, which is derived from pig eggs (hence PZP – porcine zona pellucida), causes female mammals to develop antibodies that attach and distort sperm receptors on eggs. Sperm can’t attach, so no fertilization takes place. PZP has long been used in zoos to manage animal populations. In the wild, its track record has been somewhat more mixed.

PZP keeps females ovulating long after they normally would have conceived, which can keep determined males in an exhausting state of perpetual rut. There have also been cases of horses, for example, conceiving out of season, so a foal is born in fall or even early winter instead of the spring. Sadly, the odds are stacked against either a late-born foal or its mare surviving a harsh winter, and even if they do, they’ll be in  Logistically, PZP requires multiple shots over several years, typically administered by dart. Tracking down specific animals and darting them can cost hundreds of dollars per animal. Also, some the adjuvants – substances that magnify a drug’s effect – for PZP have caused problems in their own right.

The Humane Society of the U.S. has been a particularly strong supporter of immunocontraception research, viewing it not only as an option for wildlife for but dogs and cats.

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GonaCon / Hormonal Immunocontraception: This vaccine targets reproductive chemistry further up the reproductive stream, stimulating antibodies to a hormone that in turn triggers the production of sex hormones – estrogen, progesterone, and testosterone. Animals that don’t develop sexually can’t reproduce. Unlike PZP, the effects last for several years. in fact, one shot may make an animal sterile for life.

The USDA, which developed the vaccine, is planning to seek approval from the EPA to use as a pesticide for deer, which is causing considerable concern among wildlife biologists. Not only are the EPA’s standards for drug approval considerably looser than those of the FDA (if GonaCon were to be used on zoo animals or pets, it would require FDA approval), but there is worry that classifying deer as “pests” along side rats and roaches sets a bad precedent for how society views and treats wildlife. They also worry that since state Agriculture departments regulate pesticides in many states, wildlife specialists wouldn’t have a say in when and how the vaccine would be used.  

The USDA’s fact sheet on GonaCon presents a vaccine with few side effects and the potential to control populations of everything from Norway rats to American bison  But in a meeting last March, a working group of the Association of Fish & Wildlife Managers raised a number of questions, noting the limited number of studies so -- most involving small groups of animals (in the case of bison, only 6) -- and few studies published in significant peer-reviewed journals. They also raised questions about long term effects, and data indicating that GonaCon increases the risk of pulmonary disease in male deer.

If approved as a pesticide for cervids (the wildlife biologists are also arguing for a limit to white tail deer), a strong precedent would be set for approvals involving other species. The potential market for GonaCon is enormous: anything with fur, from deer and horses, to rats and squirrels (it’s currently being used to sterilize squirrels already in San Francisco on a special research permit).

Still, there is the problem of vaccine delivery: Darting wildlife is time-consuming and expensive, costing as much as hundreds of dollars for larger animals. And there is no easy way to tell which animals have already been treated. A bait-based vaccine would be cheaper, but still wouldn’t guarantee that meaningful percentage of the population received treatment.

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Delivery by Transgenic Plant  & Virus: Researchers at Cornell University has been developing transgenic plants that deliver a dollop of immunocontraception with every nibble. Land Research, an environmental research organization in New Zealand, is particularly interested in producing a genetically modified, PZP-producing version of a plant favored by a brushtail possums, an invasive species there.

Plant-based birth control actually already exists in Nature. Over 30 years ago, Starker Leopold (son of Aldo) published a paper on plants that develop high concentrations of phytoestrogens (plant-based estrogens) in drought years, causing the quail that eat them to lay fewer eggs. it is a remarkably sensitive ecological balancing mechanism, a natural feedback loop that makes sure the bird population stays in sync with its local food supply. High concentrations of phytoestrogens from woody plant material in the effluent of paper and lumber mills has been linked sterile and sexually bizarre fish found downstream. And there are high levels of phytoestrogens in St. Anne’s Lace, a plant used in folk medicine to induce abortion. Still, a plant that causes an anti-fertility immune response would be a first. (more on phytoestrogens)

Meanwhile, researchers in Australia have recently tested a modified mouse herpes virus – mouse cytomegalovirus (MCMV) – that causes a PZP-style immune response. So far, tests have shown the virus, which is spread mouse-to-mouse, to be highly specific to a particular variety of mouse. Also, unlike poisons, it doesn’t leave a trail of destruction up the food –chain when the dead mouse is eaten by scavengers. But there is always the possibility that genes can escape to be picked up by other microbes affecting other species. Australian researchers are also working on a vaccine for rabbits, using an genetically-modified version of the myxoma virus that was brought into Australia half a century ago to wipe out…rabbits. Although the myxoma was initially successful, with a mortality rate approaching 90%, survivors emerged through natural selection and flourished.

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Contragestation: This is another word for abortion. A drug called Lutalyse, which has been approved by the FDA for livestock use, has successfully been tested on deer. it is delivered by bait during winter, when does are both pregnant and more easily attract edto bait stations.  Although effective, the cruelty of causing does to abort in the middle of winter, as well as the fact that fawns over 16 weeks old look like fawns, make this a politically fraught solution. Also, it  doesn’t prevent future pregnancies, so deer would need to be treated each and every year.

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Birds, Drugs & Side Effects: Three geese swimming in an office-park pond is a relaxing sight. Thirty, somewhat less so. Three-hundred and it’s a Alfred Hitchcock movie. Addling eggs by physically shaking them in a nest or oiling them is risky, slow work (unless you happen to be a coyote…see second half of Part 1). But there are alternatives. In the 1950s, a compound called Nicarbazin, used to control a gastrointestinal ailment in chickens, was found to have a rather serious side effect: reducing egg-laying and egg-hatching. The USDA is now testing to see whether adding the drug to goose feed would have the same affect on wild birds. At about the same time, a drug called Ornitrol (diazacholesterol) was developed as an anti-cholesterol drug for humans. Again, there were side effects and it was shelved until someone decided to try it on birds. As anyone on a heart-healthy diet knows, eggs are high in cholesterol. It turns out there’s for a reason for it and if a bird can’t generate enough cholesterol, egg quality and quantity suffer. Other anti-cholesterol drugs are also being tested. So yet another use for statins…

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SIT / Radiation: Sterile Insect Technique was the USDA’s first large-scale contraceptive scheme, dating back to the late 1930s when radiation was just coming into vogue. It has also been the most successful. Vast quantities of male flies are sterilized by radiation, chilled to a docile stupor, packed in a box, put on an airplane and released to find passion with unsuspecting females whose eggs will never be fertilized. The first actual field test took place in the 1950s in a successful attempt to eradicate the all-too-aptly named screwworm fly. It has since been used to contain all kinds of fly and moth species, including the infamous Medfly. Each week, approximately 100 million irradiated Medfly pupae are shipped into Florida from a USDA bug-nursery in Guatemala in an ongoing effort to keep Florida’s fruit crops safe.

Last year, researchers in England figured out a way to insert a genetic marker in male mosquitoes, finally making it possible to separate young males from females for use in SIT. Since males don’t bite, releasing large numbers of them is safe. They can’t spread diseases such as West Nile or malaria. (Females need blood for their eggs; males sip nectar.)

In a related scheme, farmed fish, particularly gmo fish, are being designed to be sterile, so if any escape at least they can’t successfully mate with wild fish. 

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