When news broke of the Ebola epidemic spreading through West Africa, it made headlines globally. But what many don’t realize is that this disease has been causing devastating epidemics among our closest relatives for decades. It is thought that up to a third of the world’s gorillas and chimpanzees have been killed by Ebola since the 1990s.

In fact, it is so destructive that many conservationists consider it one of the most serious threats to the survival of wild African apes, alongside hunting and deforestation. Now researchers have managed to develop the first ever orally administered vaccine specifically with the aim to conserve wild apes. In a trial, the results of which are published in Scientific Reports, the oral Ebola vaccine was tested on 10 captive chimpanzees and was found to be effective, with no side effects or stress.

But there is a snag. This trial may turn out to be the last carried out on captive chimps, as a change in the law now means that it is illegal to test vaccines on apes. The law was changed after long running campaigns and animal welfare groups stopped the practice of using chimpanzees in trials for human vaccines. The “horrible irony”, say the researchers, is that this may impact conservation efforts, as they can’t develop effective vaccines for the animals’ wild counterparts either, as many biomedical research facilities will stop housing them.

“African apes are threatened by naturally occurring pathogens like anthrax, and the increasing overspill of human pathogens such as measles,” explained lead author Dr Peter Walsh of the University of Cambridge. “A glimmer of hope lies in the fact that many of the disease threats are now vaccine preventable.”

But with current restrictions in place, it seems likely that this newly developed vaccine will not be able to progress to the stage where it could then be used on wild animals, something that would ultimately prove detrimental to the future of gorillas and chimpanzees. “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,” said Dr Walsh.

While previous attempts to vaccinate wild apes relied on using hypodermic darts with habituated animals, this is basically impossible to achieve with a rare, wide-ranging species that tends to inhabit dense rainforests. The researchers were hoping to be able to develop an oral vaccine that could then be placed in fruit or other food, which would make administering it much easier.

It seems, though, that at this time the development has to be put on hold, along with the future of our closest living relatives.