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German team solves celebrity polar bear’s death

Knut was a star at the Berlin Zoo starting as a cub in 2007, and his mysterious death at age 4 was widely mourned. European Pressphoto Agency/File

BERLIN — The sudden death four years ago of Knut, the Berlin Zoo polar bear who ended up on the cover of Vanity Fair, shocked his fans around the world and posed a riddle for veterinarians anxious to keep other animals from suffering the same fate.

What killed Knut?

The answer turned out to be even more useful than scientists could have anticipated.

Researchers in Germany said Thursday they have found the cause of the bear’s death, and the discovery may help raise awareness of a condition that affects humans, possibly saving lives.

Knut died in 2011 after suffering an apparent seizure and falling into his enclosure’s pool in front of hundreds of visitors at the zoo. His short life was a surprise: Polar bears can live up to 20 years in the wild and sometimes longer in captivity.

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A necropsy quickly established that Knut suffered from encephalitis, a swelling of the brain. Initially, scientists thought it had been caused by an infection, but that theory was later discounted.

‘‘At the beginning of 2014, we had basically exhausted every option,’’ said Alex Greenwood, from the Leibniz Institute for Zoo and Wildlife Research, which led much of the initial research into Knut’s death. Greenwood said his team shelved their samples, figuring it might take decades to figure out why the bear died.

Then they got a call from Harald Pruess, a neurologist at a Berlin hospital and researcher at the German Center for Neurodegenerative Diseases.

Pruess said he noticed that Knut’s case showed similarities to some of his human patients with anti-NMDA receptor encephalitis. The autoimmune disease, in which the body attacks its own brain cells, was discovered in humans only eight years ago. It was never previously found in animals.

‘‘It was a bit of a long shot, but after six or eight weeks we saw that it really was that,’’ Greenwood said. Their research was published Thursday in the journal Nature Scientific Reports.

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Had Knut’s keepers known what their star attraction was suffering from, they could have treated him, he said.

Humans with the condition are given cortisone, which suppresses the immune system until the body can recover. In most cases they are able to return to a normal life, though some suffer from memory problems and have difficulty concentrating.

Pruess said Knut’s case may help raise awareness of what is still a relatively unknown illness in humans. Affecting about 1 in 200,000 people each year, it can be detected with a simple procedure, he said.

Greenwood said Knut’s misfortune — he might have survived if he hadn’t collapsed into the water — was a stroke of luck for scientists.

‘‘It’s just for us incredible that the most famous bear in the world dies and it turns out to be the first description of this disease,’’ he said. ‘‘The knowledge gained from his death should benefit both human medicine, because people will . . . be more aware of it, and animal medicine.’’