Knut the Polar Bear Died From Rare Form of Encephalitis, New Report Finds

The mystery surrounding the unexpected 2011 death of Knut, a much-loved celebrity polar bear in Germany, has been solved.

The 4-year-old bear had a seizure in the German zoo where he lived, falling into a pool and drowning. The shocking death captured the attention of the world and, until now, it had been unclear what caused such a young bear to die.

In the open access journal Scientific Reports, researchers reported this week that Knut suffered from a rare auto-immune form of encephalitis that, although recorded in humans, had never been found before in animals.

Knut achieved worldwide celebrity after he was rejected by his mother and was hand-reared by a caregiver at the Berlin Zoological Garden who camped out to give the cub his bottle every two hours, The Blaze reported. A twin died after only a few days, and Knut's survival story made headlines worldwide, spawning a film appearance and merchandise.

Scientists who examined Knut after his death determined that he suffered from anti-NMDA receptor encephalitis, a severe autoimmune disease, the journal article said.

Dr Harald Prüss, from the German Center for Neurodegenerative Diseases, works with human patients who have the disease, and he told the BBC that he recognized some of the symptoms in Knut's post-mortem reports.

"Antibodies that normally help to defend us against viruses or bacteria can obviously under certain circumstances turn against their own body and attack nerve cells," Prüss said. "In the most common autoimmune encephalitis, these antibodies bind to a glutamate receptor in the brain called NMDA receptor and cause seizures, cognitive impairment, psychosis, or coma."

Anti-NMDA receptor encephalitis affects about one in 200,000 humans every year, and it is often seen as a side effect of ovarian cancer, according to the BBC.

In the journal report, Prüss and others scientists said the finding that this form of encephalitis killed Knut means that the disease "may be a disease of broad relevance to mammals that until now has remained undiagnosed."

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