Chimpanzees died mysteriously at the Tacugama Shrine in Sierra Leone in a decade or so in 2016 when Tony Goldberg began to find out why.
The sanctuary staff, veterinarians and biologists have conducted several investigations into the disease over the years. It was not contagious, did not infect humans, did not appear at other shrines, but killed chimpanzees in Tacugama in an unmistakable, worrying pattern.
“It was always in the same season and always the same symptoms,” said Andrea Pizarro, the sanctuary’s conservation manager. The chimpanzees show neurological symptoms: lack of coordination, difficulty walking and seizures. They also show signs of digestive tract, such as distended abdomen and vomiting. When the syndrome appeared, not one afflicted chimpanzee survived.
Sometimes chimpanzees that looked good one day were found dead the next, something that happens in all shrines and presumably in nature as well. But over the years, post-mortem tests have shown the same pattern of intestinal damage as the chimpanzees who showed symptoms.
The sanctuary, a major tourist attraction and the only place for orphans in Sierra Leone, houses on average just over 90 chimpanzees. It is a Western chimpanzee, a critically endangered subspecies. Fifty-six chimpanzees in Tacugama have died from this mysterious disease, in a country that recently made the chimpanzee its national animal.
What made the mystery even more surprising was that the disease pattern occurred only in Tacugama. Chimpanzees became ill and died in other shrines, of course, sometimes suddenly, but the peculiar pattern of this disease occurred in only one place. Several investigations focusing on viruses or poisonous plants yielded no clear answers.
In 2016, dr. Goldberg, an epidemiologist and veterinarian at the University of Wisconsin, Madison, and head of the Kibal EcoHealth project, was approached by the Pan African Sanctuary Alliance to solve the mystery. He and his colleagues in Wisconsin have joined forces with other veterinarians and biologists in Africa and elsewhere to undertake a comprehensive analysis of blood and tissue from the dead chimpanzees frozen in a nearby hospital.
“It took me five years,” he said. On Wednesday, he and other researchers reached a milestone in their veterinary detective work with a report in Nature Communications identifying a new species of bacteria that is clearly related to the syndrome.
So far, the bacterium has not found the sole cause of the disease, but it has opened a new window on the bacterial genus Sarcina, which may include more unknown species that threaten human and animal health.
Dr. Goldberg stressed that this was not a pandemic in the making. The bacterium is not contagious, and it is not going to cause widespread damage.
From the beginning, nothing about the study was simple, including getting the raw materials for the research to the laboratory. Dr. Goldberg attributed Ismail Hirji, a Canadian veterinarian in private practice who was the sanctuary’s clinical veterinarian in 2016, for overcoming the initial obstacles. “He has just moved mountains to retrieve these monsters from Sierra Leone,” Dr Goldberg said.
The first obstacle was the application process for permits to transport samples of diseased tissue taken from an endangered species. Dr. Hirji recalled that the paperwork took about a year.
On the day that the samples had to be sent, a police escort could not show up. Dr. Hirji and others hit a car and small boat one last time because the ferries that passengers usually transport to the airport were closed. In the boat, he said, “We actually carried 30 kilograms of monsters on our heads.”
Despite experiencing more problems at the airport, including a lack of cold storage, the group eventually took the monsters in a plane to Dr. Goldberg’s laboratory in Wisconsin.
Subsequently, researchers began an extensive screening of blood and tissue from healthy and diseased chimpanzees for viruses, bacteria and parasites using genomic studies, visual examination of the tissue and other techniques.
Leah A. Owens, a candidate for a Ph.D. and a veterinary degree obtained in Drs. Goldberg’s laboratory work, they began concentrating on bacteria after initial DNA surveys showed only one probable culprit, a bacterium that was present in 68 percent of the samples of sick chimpanzees, but none of healthy chimpanzees.
Me. Owens tried to grow the bacterium in culture and send it to other laboratories for sequencing, looking for tissue samples. Almost impossible to grow in the laboratory, the bacterium eventually multiplied in a smear of brain tissue. Under a microscope, the tissue revealed the common shapes of bacteria, spheres and cylinders. And then, she said, “I’m coming to this one that just looks muddy.”
“If you look at it straight, it looks like a four-leaf clover,” she said, “but it’s actually a four-sphere cube.”
It indicated that it belonged to the genus Sarcina, which included only two known species. One lives in the ground and the other, first identified in 1844, is called Sarcina ventriculi and was known to cause gastrointestinal symptoms in humans and animals such as those of the Tacugama chimpanzees.
In humans, Sarcina ventriculi can thrive after surgery and produce gas that fills the walls of the intestine. Once the infection reaches that stage, people almost always die.
The technical term, Dr. Goldberg said, is emphatic gastroenteritis, and “that’s what the chimpanzees had.”
While Ms Owens was investigating further, it became clear that the bacterium in the chimpanzee samples, also in the brain tissue, where an intestinal bacterium certainly does not belong, is not the same as the species that has been reported in humans and animals for many years. It was larger and the genome had significant differences.
The researchers suggested in their paper that the new species be called Sarcina troglodytae, because it occurs in chimpanzees, Pan troglodytes.
Before the proposed name can be accepted as an official new species, researchers need to make the bacteria grow more successfully. At this stage, they have only shown that the bacteria are associated with the disease, but not the cause of it.
And the disease is still mysteriously emerging. The syndrome always peaks in March, for example during the dry season. Keeping the chimpanzees indoors can prevent this. And something in their diet or environment can also play a role.
However, the researchers offered potential treatments. One drug that can be effective is omeprazole, the ingredient in Prilosec, which reduces stomach acid – an environment in which the bacteria thrives.
Some antibiotics are more effective than others. Me. Pizarro, the manager of the sanctuary, said one chimpanzee started developing the syndrome last week, but they gave antibiotics and other treatments and are doing well now. However, the syndrome can still die after a recovery.
The new bacteria, or other similar ones, may be more widespread than scientists have realized, Dr. Goldberg said. Sarcina bacteria have not been the subject of much research. The diseases and deaths in humans and animals attributed to Sarcina ventriculi can actually be caused by the new bacterium, or similar species. If this is the case, it is a group of bacteria that deserves more attention.
“It falls into the category of things we should look at,” he said, “but we should not worry.” No Sarcina pandemic is likely in the offing, he said.
But dr. Goldberg said he would not be surprised if we “see in retrospect that many human and animal diseases we have attributed to other things are actually caused by versions of this bacterium.”