Six of the rare primates have died in the past month and another 10 have fallen seriously ill at a sanctuary close to the capital, Kinshasa. With chimpanzees, they are mankind’s closest living relatives.

Vanessa Woods, a researcher at Lola Ya Bonobo, said it was heartbreaking to watch. “It starts with a cough and then they get bunged up with mucus which runs down their faces. They end up lying on their stomachs because it’s the only way they can breathe,” she said.

“When they get really bad they disappear into the forest, fall down and there’s no way we can find them.”

The sanctuary was home to 60 of the endangered apes before the disease struck. Most had been found as babies after their parents were killed for bush meat.