Between 2005 and 2018, around 53 western chimpanzees (Pan troglodytes) in the nature reserve had died of a mysterious illness that always was fatal. “It was not subtle,” researcher Tony Goldberg, a disease ecologist at the University of Wisconsin, says.
“The chimpanzees would stagger and stumble, vomit, and have diarrhea. Sometimes they’d go to bed healthy and be dead in the morning.” The sanctuary veterinarians tried everything, from various antibiotics to wrapping the chimps in blankets and isolating the sick ones, but nothing they did seemed to work.
The sanctuary is home to about 100 chimpanzees, rescued from illegal trade, hunting, or abandonment as pets. Biologist, Gregg Tully, executive director of the Pan African Sanctuary Alliance, says, “It was really upsetting for the staff because there was no end in sight.”
In 2016, Tully contacted Goldberg, seeking his help in identifying the mysterious disease. After a study of tissue samples and DNA from chimpanzees at the sanctuary, Goldberg and his colleagues have identified the likely culprit.
In the journal, Nature Communications, the researchers report that a new species of clover-shaped bacterium was identified in the infected tissue samples from 13 chimps that died. There was no sign of the bacterium in samples from 14 healthy chimps.
A new bacterium and a new disease
In 2018, one of Goldberg’s graduate students, 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 I saw this really weird-looking cubic structure,” she recalls.
This discovery was a big break for the researchers, who had spent years screening tissues, feces, and blood samples from the sanctuary chimps for pathogens, not finding anything that stood out. But Owens realized the bacteria on her slide looked like the clover-shaped Sarcina—a finding confirmed by pathologists.
The bacterium in question closely matches Sarcina ventriculi, a species found on the surface of cereal seeds, in soil, mud, and in the stomachs of humans, rabbits, and guinea pigs. In humans, S. ventriculi, sometimes cause recurrent vomiting, abdominal pain, nausea, and diarrhea. Typically, these patients are treated with antibiotics, according to Science Post.
However, genomic sequencing 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. They named the disease Epizootic Neurologic and Gastroenteric Syndrome, or ENGS.
Further studies on Sarcina troglodytae
Additional studies of the bacterium’s DNA suggest that it is more virulent than S. ventriculi. This observation also makes the research team wonder whether cases in other animal species that were classified as S. ventriculi might belong to this new species—or other unidentified types of Sarcina.
Interestingly, the disease always seems to peak in March, every year, during the dry season, yet it is still not clear how chimpanzees are infected with the pathogen. Meanwhile, Owens is applying for grants to try to identify the source of the bacterium by testing samples of water, air, food, and vegetation she and Goldberg gathered at the sanctuary in 2019.
ENGS has not been found in a human, even though the two species share about 99 percent of their hereditary material or DNA. “There are very few pathogens that infect chimpanzees without infecting humans and very few pathogens that infect humans without infecting chimpanzees,” Goldberg says, according to USA Today.
