Mystery illness killing chimpanzees for years may finally be solved by scientists

A mysterious illness that’s killed more than 50 chimpanzees may finally have been cracked by scientists.

The deadly disease caused neurological and gastrointestinal symptoms among the critically endangered Western chimpanzees at the Tacugama Chimpanzee Sanctuary in Sierra Leone.

A tragic total of 56 of the primates died from the savage illness between 2005 and 2018.

“It was always in the same season and always the same symptoms,” conservation manager Andrea Pizarro told the New York Times.

The afflicted animals showed neurological symptoms like lack of coordination and seizures, while also gripped with distended abdomens and vomiting indicating gastrointestinal distress.

“It was not subtle — the chimpanzees would stagger and stumble, vomit, and have diarrhoea,” Tony Goldberg, an epidemiologist and veterinarian at the University of Wisconsin, Madison, told Science.

“Sometimes they’d go to bed healthy and be dead in the morning.”

Desperate staff tried to nurse the sick chimps back to health, but soon realised it had a mortality rate of 100%. If an animal developed symptoms they were a goner, even if they were treated.

Gregg Tully, executive director of the Pan African Sanctuary Alliance, said the experience was “really upsetting” for sanctuary workers.

Eventually, the team got in touch with Prof Goldberg and his team in the hopes they could find out what was killing the chimps.

Researchers screened tissue and stool samples from the animals checking for viruses, bacteria and parasites.

DNA surveys identified one particular bacterial species in 68% of the samples from sick chimps, but none from the healthy chimps.

The bacterium had an unusual appearance when scrutinised under a microscope – it looked like a four-leaf clover.

This shape suggested it belonged to the Sarcina genus, which is poorly understood but includes a species that causes gastrointestinal symptoms in humans.

Genome sequencing confirmed the bacterium is closely related to other Sarcina bacteria but is itself a new species, the researchers detailed in a study published on February 4 in Nature Communications.

Although strongly associated with the chimps’ illness, the team have yet to determine whether the bacterium is the sole cause of the primate disease or if there could be other factors at play.

Much else about the chimp deaths also remains a mystery, such as why reports of the disease seem to peak in March every year.

One theory suggests the bacterial spores are common in the general environment but weather conditions in Sierra Leone or even the chimps’ own biology could trigger the illness.

Vets at the Tacugama sanctuary are now using the researchers’ findings to treat sick chimps with antacids and antibiotics, both of which have successfully treated Sarcina infections in humans.