Now a researcher in the College of Veterinary Medicine at the University of Georgia, Fayrer-Hosken has led a team of large animal scientists in the development of a birth-control vaccine that promises to safely and humanely control elephant populations. His study, reported in the latest issue of the science journal Nature, involved the vaccine, pZP, whose key ingredient is a protein taken from the coating of pig eggs. The protein prevents fertilization by raising antibodies in female elephants that masks their eggs from intruding sperm.
Field trials of the contraceptive were conducted at Kruger National Park in northeastern South Africa, where strict anti-poaching law enforcement and effective conservationist strategies have allowed the elephant population to approach a high of nearly 9,000. Park officials there are concerned that the aggressive “browsing” of the free-roaming elephants in the 4.8 million-acre area is now damaging other animal and plant species in the ecosystem, as have expanding elephant herds in other parts of Africa where conservation efforts are strong.
Elephants remain a threatened species in many African countries, to be sure. But in areas where rifle-toting and bush-bulldozing humans are held at bay, elephants have “no natural terminal predators,” says Fayrer-Hosken. What does come naturally to them is destroying the plentiful Marula trees, whose leaves and roots they love to munch. The loss of many trees in the reserve now threatens a number of baboon, bird, and insect species also dependent on the Marula for survival, he says.
The effort to develop the elephant contraceptive was a high-tech enterprise. Herds of elephants were tracked by helicopter, and females anesthetized with aerial darts. The research team then descended upon the downed and woozy females, conducting on-the-spot ultrasound tests to check for pregnancy. Of 41 non-pregnant elephants identified, 21 were given the pZP vaccine and 20 were given placebo vaccines. All were fitted with radio collars and released back into the wild. Booster shots were administered two times later through aerial darts.
After twelve months, most of the elephants were recaptured and reexamined. Of those who had received the placebo, 89 percent were pregnant. Of those who had received the pZP vaccine, only 44 percent were pregnant. Encouraged by the results, another study was done with ten more Kruger National Park elephants, who this time were given booster shots earlier and tracked via a global positioning satellite so as to allow researchers to keep constant track of their movements. After ten months, only two of the ten recovered elephants were pregnant.
Besides developing an immunocontraception vaccine that is at least 70 percent effective in elephants, the research project also yielded another positive result. Field observations indicate that the vaccine causes none of the behavioral abnormalities among female elephants that have occurred in association with hormonal contraceptive implants. In the past, says Fayrer-Hosken, females with such implants would separate themselves from the herd, abandoning their calves and “running around a little crazy.” The elephants treated with the pZP vaccine did not stray from their family units. And when the vaccine wore off, they began menstruating again.
Fayrer-Hosken says the research team will continue to monitor the elephants and to conduct field experiments, with the goal of developing a vaccine that will work effectively with a one-dose shot. Because the pig protein-based vaccine could probably be modified to develop contraceptive drugs for other large mammals, he believes the results bode well for other species. “Basically, any animal in competition with man for space can be controlled in a compassionate way,” he says. “Deer is certainly one mammal that springs to mind. But there are many.”
