They are hunted for their meat, their hands are used as charms and their forest habitat is under threat from industrial logging and oil palm plantations — but the biggest threat to Africa’s gorillas now comes not from Man, but from ebola.

The haemorrhagic fever has killed more than 11,000 people since 2013, and up to a third of the world’s gorillas in the forests of the Congo basin, where ebola was discovered almost 40 years ago.

Scientists are uncertain how the virus spreads between species, or how it survives between outbreaks, but researchers at the University of Cambridge hope to save the great apes with a vaccine, which could be tested on them as early as next year.

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“Gorillas have got enough other problems — hunting in particular,” said Peter Walsh, a primate ecologist at the university. “Preventive medicine is a no-brainer.”

A human ebola vaccine, developed by the Public Health Agency of Canada, and tested in Guinea this year, appeared to offer complete protection to the more than 2000 people it was administered to, but the animal version is different. It is based on a rabies treatment that Dr Walsh says has been used successfully on foxes and adapted to carry an ebola protein. It has been tested on captive gorillas and could be given to wild apes by March next year.

The trials, in the Republic of the Congo, would be the first time an oral vaccine had been tested on an endangered species, Dr Walsh said, but they risked being derailed by welfare groups opposed to testing on animals. “The wildlife establishment has been totally cowed by the animal welfare community and the anti-vaccine lobby. The fear of being labelled vivisectionists has paralysed them,” he said.

Some conservationists are wary of vaccinating wild animals because it crosses the line between observation and intervention. Researchers and tourists are routinely required to wear face masks when they visit habituated apes to prevent the spread of diseases — so in many instances that line has already been crossed. Habituated animals are not tame, but they are used to a human presence.

“It’s for their protection, not ours,” said Steve Bebou, an assistant researcher at the Mondika research camp, next to Nouabale-Ndoki national park, in the far north of the country. As he spoke, a vast silverback known as Kingo lumbered past on his knuckles a few feet away from where we were standing.

The scientists try to keep their distance, but once the apes are habituated it’s almost impossible to stop the inquisitive toddlers approaching — and any actions designed to scare them away would risk the wrath of their parents.

Getting to Mondika involves a three-hour hike, part of it through waist-deep water, and another hour’s walk from the camp to the gorillas.

Almost half of the 40,000 western lowland gorillas recorded in Odzala national park in 2005 had disappeared by 2012 because of hunting and ebola, researchers said. “Each human outbreak has been accompanied by reports of gorilla and chimpanzee carcasses in neighbouring forests,” a 2008 study published in the journal Science claimed.

Fruit bats are known to carry Marburg virus, which is in the same family as ebola, and scientists suspect they may also carry ebola. It is also thought that although some gorillas die the same horrible death as humans with ebola, others are carriers of the virus.

“Very few people believe ebola is ever going to wipe out great apes in central Africa,” Dr Cameron said. “But as we continue to put more and more pressure on these forests, it might reduce the populations to such a level that these other insults, like logging, hunting, loss of habitat, have much more of an impact than they do today.”