Chimpanzees had been mysteriously dying in the Tacugama Sanctuary in Sierra Leone for about a decade when Tony Goldberg worked to figure out why in 2016.

Sanctuary staff, veterinarians, and biologists had conducted several examinations of the disease over the years. It was not contagious, did not infect people, did not appear in other sanctuaries, but instead killed chimpanzees in Tacugama in an unmistakable, alarming pattern.

“It was always the same season and always the same symptoms,” said Andrea Pizarro, the sanctuary’s nature conservation manager. The chimpanzees showed what appeared to be neurological symptoms: lack of coordination, difficulty walking, and seizures. You would also show signs of gastrointestinal discomfort, such as: B. distended abdomen and vomiting. When the syndrome occurred, not a single chimpanzee survived.

Sometimes chimpanzees that appeared fine one day were found dead the next, which occurs in all sanctuaries and, presumably, in the wild. But over the years, post-death tests had shown the same pattern of gut damage as the chimpanzees showing symptoms.

The sanctuary, a major tourist attraction and the only orphaned chimpanzee site in Sierra Leone, is home to just over 90 chimpanzees on average. These are western chimpanzees, an endangered subspecies. Fifty-six chimpanzees in Tacugama have died of this mysterious disease, in a country that recently made the chimpanzee its national animal.

What made the puzzle even more puzzling was that the clinical picture only appeared in Tacugama. Chimpanzees got sick and of course sometimes died suddenly in other sanctuaries, but the peculiar pattern of this disease only appeared in one place. Several studies that focused on viruses or toxic plants did not provide clear answers.

In 2016, Dr. Goldberg, an epidemiologist and veterinarian at the University of Wisconsin, Madison, and director of the Kibale EcoHealth project, approached by the Pan African Sanctuary Alliance to try to solve the mystery. He and his colleagues in Wisconsin teamed up with fellow veterinarians and biologists in Africa and elsewhere to carry out a comprehensive analysis of the blood and tissues of the dead chimpanzees that had been 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 type of bacteria clearly linked to the syndrome.

So far, research hasn’t found the bacteria to be the sole cause of the disease, but it has opened a new window on the Sarcina bacterial genus, which may include unidentified species that threaten human and animal health.

Dr. Goldberg stressed that this is not a pandemic. The bacterium is not contagious and will not cause widespread harm.

From the start, nothing about the study was straightforward, including handing the raw materials over to the laboratory for research. Dr. Goldberg credited Ismail Hirji, a Canadian private practice veterinarian who was the sanctuary’s clinical veterinarian in 2016, with overcoming these initial obstacles. “He just moved mountains to get these samples from Sierra Leone,” said Dr. Goldberg.

The first hurdle involved the application process for permits to transport samples of diseased tissue taken from an endangered species. The paperwork took about a year, recalled Dr. Hirji.

The required police escort did not appear on the day the samples were due to be shipped. Dr. Hirji and others made a last-minute car and small boat rush because the ferries that normally take travelers to the airport had closed. In the boat he said, “We essentially had 30 kilos of samples on our heads.”

Despite major difficulties at the airport, including a lack of refrigeration rooms, the group eventually took the samples to Dr. Goldberg’s laboratory in Wisconsin.

Next, researchers began a comprehensive screening of the blood and tissues of healthy and sick 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 resulting in Dr. Goldberg’s lab began to focus on bacteria after initial DNA tests showed only one likely culprit, a bacterium found in 68 percent of samples from sick chimpanzees but none from healthy chimpanzees.

Ms. Owens tried to grow the bacterium in culture, sent it to other laboratories for sequencing, and looked for it in tissue samples. It was almost impossible to grow in the laboratory, and the bacterium eventually reproduced in a brain tissue swab. Under a microscope, the tissue showed the common shapes of bacteria, spheres and cylinders. And then she said, “I come to this one who just looks crazy.”

“If you look at it directly, it looks like a four-leaf clover,” she said, but it’s actually a four-ball cube.

This 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 is known to cause gastrointestinal symptoms in humans and animals such as those suffered by the Tacugama chimpanzees.

In humans, sarcina ventriculi can thrive after surgery and produce gas that fills the intestinal walls. Once the infection reaches this stage, people almost always die.

The technical term, said Dr. Goldberg, is emphysematous gastroenteritis, and “that was what the chimpanzees had.”

As Ms. Owens investigated further, it became clear that the bacterium in the chimpanzee samples, including brain tissue, which an intestinal bacterium certainly did not belong to, was not the same as the species reported for many years in humans and animals. It was larger and its genome was significantly different.

In their work, the researchers suggested naming the new species Sarcina troglodytae, as it was found in chimpanzees, Pan troglodytes.

Before the proposed name can be accepted as an official new species, researchers need to grow the bacteria more successfully. At this point they only showed that the bacteria are associated with the disease, not its cause.

And the disease still occurs in a mysterious way. The syndrome always reaches its peak in March, for example during the dry season. Leaving the chimpanzees inside in the afternoon seems to prevent this. And something in their diet or their environment can play a role as well.

However, the researchers have offered possible treatments. One drug that may be effective is omeprazole, the ingredient in Prilosec, which reduces stomach acid – an environment in which the bacterium thrives.

Some antibiotics are more effective than others. Ms. Pizarro, the sanctuary’s director, said a chimpanzee started developing the syndrome last week but they gave him antibiotics and other treatments and is fine now. However, the syndrome can still be fatal after recovery.

The new bacterium, or similar bacteria, may be more common than scientists realize, said Dr. Goldberg. Sarcina bacteria have not been studied much. The diseases and deaths in humans and animals attributed to Sarcina ventriculi may actually be caused by the new bacterium or a similar species. If so, this is a group of bacteria that deserve more attention.

“It falls under the category of things to watch,” he said, “but don’t fret.” It is likely that no Sarcina pandemic is imminent, he said.

Dr. However, Goldberg said he would not be surprised if “with hindsight we realized that many human and animal diseases that we had attributed to other things are actually caused by versions of these bacteria.”