ABOVE: Sarcina ventriculi, a bacterium that causes gastrointestinal symptoms in humans and is related to the Sarcina species found in chimps.

Scientist sleuths may have solved the mystery of why chimps have been dying at a sanctuary in Sierra Leone. In a study published today (February 3) in Nature Communications, the researchers describe a new species of bacterium in the genus Sarcina that’s associated with a deadly disease of critically endangered Western chimpanzees (Pan troglodytes verus).

The disease, which causes neurological and gastrointestinal symptoms, killed 56 chimps at the Tacugama Chimpanzee Sanctuary in Sierra Leone between 2005 and 2018. “It was not subtle—the chimpanzees would stagger and stumble, vomit, and have diarrhea,” study author Tony Goldberg, an epidemiologist and veterinarian at the University of Wisconsin, Madison, tells Science. “Sometimes they’d go to bed healthy and be dead in the morning.”...

The sanctuary’s staff noticed that the condition was 100 percent fatal—if chimps developed symptoms of the disease, they never recovered, even if treated, Science reports. “It was really upsetting for the staff,” Gregg Tully, executive director of the Pan African Sanctuary Alliance, tells Science.

To get to the bottom of the chimps’ affliction, the alliance called Goldberg and his team for help, according to The New York Times. The team screened chimp tissue and stool samples for viruses, bacteria, and parasites. DNA surveys revealed that one bacterial species was found in 68 percent of samples from sick chimps, but in none of the healthy chimps. Under the microscope, the bacterium looked like a four-leaf clover, Leah Owens, a graduate student in Goldberg’s lab, tells the Times. According to the newspaper, this unusual shape suggested that it belonged to Sarcina, a poorly studied genus that includes a species that causes gastrointestinal symptoms in humans. 

Genome sequencing of the bacterium confirmed that it is closely related to other Sarcina bacteria but is a new species. Although the bacterium is strongly associated with the chimps’ illness, the researchers haven’t yet figured out whether the bacterium alone causes disease or if other factors are involved.

Several other mysteries regarding the disease also have not yet been solved. It’s not clear where the bacterium comes from and why the disease peaks in March each year. One possibility is that the bacterium’s spores are common in the environment, but weather conditions or the chimps’ biology triggers the disease, Science reports.

According to Science, veterinarians at the Tacugama sanctuary are drawing on the researchers’ findings to treat sick chimps with antacids and antibiotics—similar to treatment of Sarcina infections in humans.

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