As animal welfare advocates and conservationists celebrated the recent phasing out of scientific experiments conducted on captive chimpanzees, Peter Walsh of the University of Cambridge and his team worked at a feverish pitch. They had been testing an oral Ebola vaccine in Louisiana for wild apes when it was announced that expanded Endangered Species Act protections would soon close a loophole that excluded captive chimpanzees, sharply curtailing biomedical research involving the primates.

"We expedited all the preparations for the trial in order to complete it before the new regulations took effect," Walsh, a biological anthropologist, told Seeker.

The results of their work, published in the journal Scientific Reports, indicate that the new oral Ebola vaccine holds promise for safeguarding wild chimpanzees and other primates from the deadly virus. It is estimated that Ebola killed a third of the world's wild gorilla population over the last three decades.

The findings complicate the ethical debate over whether or not to conduct biomedical research on captive chimpanzees, particularly when the therapeutics in question are targeted to save the lives of primates. Humans willingly participate in drug trials, "but with chimpanzees," Walsh said, "there is no possibility of informed consent or voluntary participation. You either do the testing on captive animals, or wild animals die."

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The researchers monitored the chimps up to 28 days afterward. Blood tests determined that levels of antibodies against the Ebola virus rose about equally in all of the primates, suggesting that oral delivery was just as effective as the shots.

"The vaccine would be used in a bait, which the [wild] apes would voluntarily eat, therefore immunizing themselves," Schnell explained. "This is similar to what has been done to eliminate the rabies virus threat to foxes in Europe."

The scientists closely monitored the chimps for behavioral and biological signs of stress throughout the research trial. Other than minor weight loss of about 2 percent of total body mass, signs of trauma were "entirely absent," they reported. Walsh likened the stress to what college students experience when anticipating exams.

The test subject chimps are now "alive and in good health," he noted, adding that the primates will soon be retired to a sanctuary.

Photo: Chimps at the Tacugama Chimpanzee Sanctuary in Sierra Leone. Credit: Jeremy Weate, Wikimedia Commons

While the fate of the chimps appears clear, the future of an oral Ebola vaccine for wild primates as well as other possible vaccines for these animals remains an unknown at this point. The researchers say that additional tests are needed before this and any other possible vaccines should be deployed, but their biomedical research trial is the last on captive chimps for now.

The application of an oral vaccine in a range of wild areas would likely inoculate more apes than would be covered by using hypodermic darts to painstakingly vaccinate a few apes at a time. But field trials involving wild apes are needed to demonstrate an oral vaccine's reach, and additional work will be required to stabilize the vaccine against the heat of forest environments where the primates live.

Photo: Rabies vaccine in a bait found at the Põhja-Kõrvemaa Nature Reserve, Estonia. The text on it reads: "Oral solution. For veterinary use only. Do not touch!"Credit: Wikimedia Commons

The CDC has documented both human and domesticated animal contacts with oral vaccine baits that were distributed to help prevent rabies in multiple states. If such baits are freely scattered, almost any animal could consume them. Individual animals — even from the target species — could also eat several baits, potentially putting them in danger.

Walsh and his team are investigating solutions to these possible problems, such as using automated camera traps to record rates of bait uptake and to better control overall vaccine distribution.

Regarding the future of captive chimpanzee trials, the scientists said such experiments are technically still legal in the US in instances meant to benefit the species. Limited funding and unwillingness on the part of zoos and sanctuaries to permit such testing on their animals pose immense challenges, however.

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"We have developed a very promising tool for inoculating ape species against the myriad deadly diseases they face in the wild, but continued progress relies on access to a small number of captive animals," Walsh said in a statement. "This may be the final vaccine trial on captive chimpanzees: a serious setback for efforts to protect our closest relatives from the pathogens that push them ever closer to extinction in the wild."

The researchers remain hopeful that the National Institutes of Health or a private funder will step forward to bear the cost of supporting chimps at a facility where conservation trials could be done.

They initiated their Ebola vaccine work with studies on mice, but those are not enough to warrant regular usage of the vaccine in primates. They further believe that alternatives to drug tests on live animals, such as in vitro experiments, do not provide adequate results.

The researchers additionally mentioned that Ebola is just one of many viruses impacting wild primate populations now. Others include malaria, anthrax and SIV, which is a virus closely related to HIV.

The new study, Walsh said, "is about developing the capacity to prevent or treat all of these disease threats. We do it for our children. Why shouldn't we do it for our wild cousins?"