Chimpanzees were mysteriously dying in the Tacugama sanctuary in Sierra Leone for about a decade in 2016, when Tony Goldberg started working to find out why.
Sanctuary staff, veterinarians and biologists have conducted several investigations of the disease over the years. It was not contagious, it did not infect humans, it did not appear in other sanctuaries, but it killed chimpanzees in Tacugama in an unmistakable and alarming pattern.
“It was always in the same season and always the same symptoms,” said Andrea Pizarro, the conservation manager for the sanctuary. Chimpanzees would show what appeared to be neurological symptoms: lack of coordination, difficulty walking and seizures. They also exhibited signs of gastrointestinal discomfort, such as a distended abdomen and vomiting. If the syndrome appeared, no affected chimpanzee survived.
Sometimes chimpanzees who looked good one day were found dead the next, something that happens in all sanctuaries and, presumably, in the jungle as well. But over the years, tests after death have shown the same pattern of intestinal damage as chimpanzees with symptoms.
The sanctuary, a major tourist attraction and the only place for orphaned chimpanzees in Sierra Leone, is home to an average of just over 90 chimpanzees. These are western chimpanzees, a critically endangered subspecies. Fifty-six chimpanzees in Tacugama died of this mysterious disease, in a country that recently made the chimpanzee its national animal.
What made the mystery even more intriguing was that the pattern of the disease occurred only in Tacugama. Chimpanzees got sick and died in other sanctuaries, of course, sometimes suddenly, but the peculiar pattern of this disease occurred in only one place. Several investigations that focused on viruses or toxic plants have not produced clear answers.
In 2016, Dr. Goldberg, an epidemiologist and veterinarian at the University of Wisconsin, Madison, and head of the Kibale EcoHealth Project, was approached by the Pan African Sanctuary Alliance to try to solve the mystery. He and his colleagues in Wisconsin joined forces with other veterinarians and biologists in Africa and elsewhere to carry out a comprehensive analysis of the blood and tissue of dead chimpanzees that were 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 that identified a new species of bacteria clearly linked to the syndrome.
So far, the research has not found the bacteria to be the sole cause of the disease, but it has opened a new window for the bacterial genus Sarcina, which may include more unidentified species that threaten the health of humans and animals.
Dr. Goldberg emphasized that this was not a pandemic in the making. The bacterium is not contagious and is not about to cause widespread damage.
From the beginning, nothing about the study was simple, including taking the raw material for the research to the laboratory. Dr. Goldberg credited Ismail Hirji, a Canadian veterinarian in private practice who was the clinical veterinarian at the sanctuary in 2016, for overcoming these initial obstacles. “He just moved mountains to take these samples from Sierra Leone,” said Goldberg.
The first obstacle involved the process of applying for licenses to transport samples of diseased tissue taken from an endangered species. The paperwork took about a year, Hirji recalled.
The day the samples were sent, a necessary police escort did not appear. Dr. Hirji and others ran a last-minute car and small boat race because the ferries that normally transport travelers to the airport had closed. On the boat, he said, “We were basically carrying 30 kilos of samples on our heads.”
Despite encountering further difficulties at the airport, including a lack of refrigerated storage, the group finally got the samples on a plane to Dr. Goldberg’s laboratory in Wisconsin.
Next, the researchers began a wide screening of blood and tissue from healthy and sick chimpanzees in search of viruses, bacteria and parasites, using genomic studies, visual examination of the tissue and other techniques.
Leah A. Owens, a doctoral candidate and a veterinarian working in Dr. Goldberg’s laboratory, began to focus on bacteria after initial DNA research showed only one likely culprit, a bacterium that was in 68 percent of samples from sick chimpanzees , but none of healthy chimpanzees.
Mrs. Owens tried to grow the bacterium in culture by sending it to other laboratories for sequencing, looking for it in tissue samples. Almost impossible to grow in the laboratory, the bacteria finally proliferated in a patch of brain tissue. Under a microscope, the tissue revealed the common forms of bacteria, spheres and cylinders. And then, she said, “I came to this one that just doesn’t look like it.”
“When you look at it from the front, it looks like a four-leaf clover,” she said, but it’s actually a four-sphere cube.
This indicated that it belonged to the genus Sarcina, which included only two known species. One lives on 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 suffered by Tacugama chimpanzees.
In humans, Sarcina ventriculi can thrive after surgery and produce gas that fills the walls of the intestine. When the infection reaches this stage, people almost always die.
The technical term, said Goldberg, is emphysematous gastroenteritis and “this is what chimpanzees had”.
As Owens investigated in more detail, it became clear that the bacteria in chimpanzee samples, including brain tissue, where an intestinal bacterium certainly did not belong, was not the same as the species reported in humans and animals for many years. It was larger and its genome had significant differences.
The researchers proposed in their article that the new species be called Sarcina troglodytae, because it was found in chimpanzees, Pan troglodytes.
Before the proposed name can be accepted as a new official species, researchers need to grow the bacteria more successfully. At this stage, they showed only that the bacteria is associated with the disease, but not its cause.
And the disease still appears mysteriously. The syndrome always peaks in March, during the dry season, for example. Keeping chimpanzees indoors in the afternoon seems to help prevent it. And something in your diet or environment can also play a role.
The researchers, however, 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. Mrs. Pizarro, the sanctuary manager, said a chimpanzee started to develop the syndrome last week, but they gave antibiotics and other treatments and are now doing well. The syndrome, however, can still kill after what appears to be a recovery.
The new bacteria, or similar ones, may be more widespread than scientists imagined, said Goldberg. The Sarcina bacterium has not been subjected to much research. The diseases and deaths in humans and animals attributed to Sarcina ventriculi may, in fact, be caused by the new bacteria or similar species. In this case, this is a group of bacteria that deserves more attention.
“It falls into the category of things we should watch,” he said, “but we don’t care.” No Sarcina pandemic should be in sight, he said.
But Goldberg said he would not be surprised if, “in retrospect, we recognize that many of the human and animal diseases that we attribute to other things are actually being caused by versions of this bacterium.”