Chimpanzees and great apes in Africa are under threat from Ebola, according to experts. Pat Sullivan / AP

The current Ebola crisis has taken a terrific toll in West Africa, stressing budgets, stretching fragile health systems to the breaking point and leaving more than 8,600 people dead since it returned to the region early last year. But seldom noted is the toll Ebola has taken on some of the world’s most endangered creatures — the great apes.

Although this outbreak now shows signs of slowing — thanks to the heroic work of local medical professionals and a large influx of foreign aid and volunteers — the disease has continued to ravage West Africa’s gorilla and chimpanzee communities since at least the early 1990s, the Global Post reports.

As with humans, the disease sporadically flares up in primate communities.

“In the last two decades, Ebola has been responsible for several catastrophic great ape population declines,” writes Ria Ghai of the Jane Goodall Institute of Canada. As an example, Ghai cites an Ivory Coast chimpanzee community reduced by half in an outbreak of Ebola in the Tai Forest that lasted two years.

“When all Ebola mortality is summed together,” according to Ghai, “an estimated one-third of the world’s gorillas and chimpanzees have been killed by this disease.”

Ebola now ranks along with poaching and deforestation as the major threats to Africa’s ape population.

And the widespread primate outbeaks can increase the risk to humans. Contact with the dead bodies of chimps in Gabon “likely led to the three secondary epidemics in humans” between 1994 and 1997, according to the Goodall Institute.

Like with previous outbreaks, the current human epidemic began with animal contact. Ebola has so far proven unsustainable in human populations without an animal vector. The fear is that as human populations expand and wildlife habitats dwindle, contact with infected animals will become more frequent.

There are still an estimated 100,000 gorillas and between 150,000 and 250,000 chimpanzees left in the wild — alongside more than seven billion humans.