Between 2005 and 2018, scientists observed that an unknown disease — that causes neurological and gastrointestinal symptoms — killed 56 chimps at the Tacugama Chimpanzee Sanctuary in Sierra Leone.
In a study published on Wednesday, Feb. 3, in the journal Nature Communications, researchers describe a new species of bacterium in the genus Sarcina that they believe to be responsible for the mysterious chimp deaths in Sierra Leone.
As chimps and humans share about 99 percent of their hereditary material, or DNA, scientists warn that there is a possibility the disease could make a jump to our species — though no human case has been identified.
Describing the disease to Science, study author Tony Goldberg, an epidemiologist and veterinarian at the University of Wisconsin, Madison, 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 Sierra Leone sanctuary's staff observed that the condition was 100 percent fatal. Though they received treatment, none of the chimps that developed symptoms of the disease ever recovered, Science reports.
Searching for the cause of the deadly chimp disease
In order to find out what was causing the disease, the Pan African Sanctuary Alliance contacted Goldberg and his team, The New York Times reports.
The University of Wisconsin researchers screened chimp tissue and stool samples for viruses, bacteria, and parasites and they found that one particular bacterial species was found in 68 percent of samples from chimps that were displaying symptoms. The bacterium did not show in any of the chimps that were not ill.
The four-lead clover shape of the bacterium suggested that it belonged to Sarcina, a poorly studied genus that includes a species that affects humans with gastrointestinal symptoms, The Scientist reports.
By genome sequencing the bacterium, the scientists confirmed that it is a new species that is closely related to other Sarcina bacteria. The researchers propose the new species should be named Sarcina troglodytae, after the species of chimpanzee it infects — Pan troglodytes.
Several mysteries do still remain — namely, the researchers have yet to figure out whether the bacterium is the sole cause of the disease, or whether other factors are involved. It is also not clear why the disease peaks in March each year, though weather conditions or the chimps' biology may be a factor, Science writes.
New treatment strategy and potential for human infection
For the moment, the researchers' findings have led veterinarians at the Tacugama sanctuary to attempt to treat the sick chimps with antacids and antibiotics, in a similar fashion to Sarcina infection treatment in humans.
Though our close relation to chimpanzees means the sanctuary has a wealth of information and potential treatments to draw from, there is also a risk that the disease could make a jump to humans, much in the same way coronaviruses jump to humans — usually via an intermediate host animal.
"There are very few pathogens that infect chimpanzees without infecting humans and very few pathogens that infect humans without infecting chimpanzees," Tony Goldberg explained to USA Today.
Lethal diseases, such as Ebola and HIV, have jumped from great apes to humans, while influenza, polio, and very recently leprosy, have passed in the opposite direction, from humans to apes.
"The staff at Tacugama (Sanctuary in Freetown, Sierra Leone) are super worried. It looks like something we need to be concerned about," Goldberg said.
As 100 percent fatal diseases are incredibly rare — Ebola has a 50 percent mortality rate while the mortality rate of COVID-19 is thought to be less than 1 percent — the scientific community is keeping an eye on developments in and around the Tacugama Chimpanzee Sanctuary in Sierra Leone.