Young chimpanzees are placed in small enclosures to minimize exposure to a lethal disease at the Chimpanzee Sanctuary of Tacugama in Sierra Leone.
Leah Owens
By Ann Gibbons
Disease ecologist Tony Goldberg was surprised in 2016 when he learned that a mysterious infection was quickly killing chimpanzees in a lush sanctuary in the Sierra Leone rainforest. “It wasn’t subtle – chimpanzees staggered and stumbled, vomited and had diarrhea,” recalls Goldberg, from the University of Wisconsin, Madison. “Sometimes they went to bed healthy and died in the morning.”
Even when veterinarians administered antibiotics and fluids to sick chimpanzees, wrapped them in warm blankets and isolated them in smaller compartments to try to prevent the infection from spreading, they died. At least 53 died at the Tacugama Chimpanzee Sanctuary between 2005 and 2018.
The refuge is home to about 100 chimpanzees rescued from illegal trade, hunting or abandoning as pets. “It was very disturbing for the team because there was no end in sight,” said biologist Gregg Tully, executive director of the Pan African Sanctuary Alliance. He sought Goldberg’s help to identify the disease, which is 100% fatal.
Now, after studying chimpanzee tissue and DNA samples at the sanctuary, Goldberg and his colleagues have identified the likely culprit. Inside Nature Communications today, they report that a new species of clover-shaped bacteria has infected tissue samples from 13 chimpanzees that have died, but not samples from 14 healthy chimpanzees.
The mysterious gastrointestinal and neurological disease did not infect veterinarians or other humans. Your closest relative is Sarcina ventriculi, however, a rare cause of gastrointestinal disease that infects people, as well as cattle, cats and horses. Although researchers are concerned about any new disease that may occur between monkeys and humans, their main concern is that it will spread to chimpanzees in other sanctuaries and in nature. “Wild animals in sanctuaries are always the most vulnerable to airborne pathogens,” says veterinary epidemiologist Sharon Deem of the St. Louis Zoo, who is not on the team.
The big break came in 2018, when Goldberg graduate student Leah Owens spotted a strange-looking bacterium in the brain tissue of one of the deceased chimpanzees. “Late at night, I was looking through the microscope and saw a really strange looking cubic structure,” she recalls. The team spent several years examining tissues, feces and blood samples from chimpanzees at the sanctuary in search of pathogens, without finding smoking evidence. Owens noticed that the bacteria on his blade looked like a clover Sarcinan– a finding confirmed by pathologists.
The researchers then sequenced the bacterium’s genome in the sample, finding it was more like that of S. ventriculi. However, it was distinct enough to classify it as a new species, which they propose to call Sarcina troglodytae, after the species of chimpanzee it infects –Pan troglodytes.
Other DNA studies of the new species of bacteria show that it has genes that make it more virulent than S. ventriculi. The team also wonders whether cases in other animal species that have been classified as S. ventriculi may belong to this new species – or other unidentified types of Sarcina.
Owens is applying for donations to try to identify the origin of the bacteria by testing samples of water, air, food and vegetation that she and Goldberg collected at the sanctuary in 2019. One possibility is that the bacteria is omnipresent, but something in the environment at the sanctuary or in monkey physiology is triggering disease. Most cases occur every March during the hot and dry season, when animals receive more food.
Veterinarians at the Tacugama sanctuary are already using the new findings: they are treating a sick chimpanzee with antacids, anticonvulsants and antibiotics – similar to treatment in humans – in the hope of saving his life. Meanwhile, other researchers hope to test the infection on chimpanzees in other sanctuaries.