Since 2005, at least 56 western chimpanzees have fallen sick with a mysterious lethal disease in the Tacugama Chimpanzee Sanctuary in Sierra Leone. After being sluggish with a lack of coordination, the chimps go on to develop vomiting and even seizures. Even after receiving extensive medical treatment by veterinarians, the overwhelming number of chimps eventually die.
The cause of the disease – dubbed “epizootic neurologic and gastroenteric syndrome” (ENGS) – had long remained mysterious, but thanks to years of veterinary sleuthing, a team of scientists believe they have found the culprit: a newly discovered species of bacteria named Candidatus Sarcina troglodytae.
The team reported their findings in the journal Nature Communications this week.
The bacteria was pinned down by searching for viruses, parasites, and bacteria within all manner of samples taken from western chimpanzees – a critically endangered subspecies – at Tacugama Chimpanzee Sanctuary with ENGS, comparing them to ones taken from healthy individuals.
Eventually, they noticed that up to 68 percent of the sick chimps carried a certain bacteria that wasn’t found in any of the healthy chimps, which was later named Ca. S. troglodytae. Most unusually, this bacteria wasn’t just discovered in the gastrointestinal tracts of infected individuals, but also embedded in their internal organs including the brain.
While this bacteria is a newly identified species, other members of the Sarcina genus are fairly well-known and are known to be common in soil. Other species have been detected in the human microbiome too. S. ventriculi, for example, has been in the stomach contents of humans suffering from recurrent vomiting and has been linked to a range of symptoms, such as abdominal pain, nausea, vomiting, diarrhea, and weakness. In these cases, the patients are often treated with antibiotics successfully. Now Ca. S. troglodytae has been identified within the sick chimps, the team hopes they can open the door to treatment for this grim disease.
Rest assured, however, the cases of ENGS in Tacugama Chimpanzee Sanctuary are unlikely to spark a global plague that ravages chimps or humans. The study authors write that “human cases have not been reported, even among personnel with close daily contact with affected individuals.” It’s still unclear how the chimpanzees became infected with the bacteria, but it's apparent the bacteria could be living in their surrounding environment since members of the Sarcina genera are found in water and soil across the world.
"Many questions regarding ENGS and 'Ca. S. troglodytae' remain unexplained," the study concludes.
Although mystery remains, a deeper understanding of this newly identified bacteria helps to uncover more information about the wider genus Sarcina and how it affects humans. Since Ca. S. troglodytae can be found in the brains of chimps, perhaps S. ventriculi can also affect the central nervous system of humans. The study adds: "We advocate that prior and future human and animal cases of severe disease associated with sarcinae, particularly those cases without clear predisposing factors, be revisited."