CASE SOLVED -The Mystery of Knut the Polar Bear’s Death at the Berlin Zoo

Two polar bear cubs, Knut and his brother, were born in in 2006 at the Berlin Zoo in Germany. Knut’s brother was rejected by his mother Tosca and died at a young age. Knut was well known worldwide until his unexpected death four years later. This was a big shock, as polar bears can survive for up to 20 years in the wild and even longer in captivity.

On March 19th, 2011, Knut had a seizure and collapsed into the pool in the enclosure before hundreds of visitors. From the necropsy, the vet staff concluded that the young polar bear had died of encephalitis (swelling of the brain) likely caused by an infection, virus, or parasite. They then ruled out all infections and the underlying cause became a mystery. They kept samples of Knut’s tissue and exhausted every testable option. For four years they would continue to try to find an underlying cause, but this mystery would remain unsolved… until now.

A neurologist from the Charite Hospital in Berlin, Dr. Harald Prüss, would be the one to finally solve the mystery. Not only was he a neurologist, but he was also a principal researcher from the German Center for Neurodegenerative Diseases. He saw similarities between Knut’s case and some of his human patients, concluding that Knut was suffering from anti-NMDA receptor encephalitis, which is a non-infectious autoimmune disease where the body attacks its own brain cells by attacking the NRI subunit of the NMDA type glutamate receptor. This disease is relatively new and was discovered in humans only eight years ago. The disease causes headaches, nausea, low-grade fever, psychosis, epileptic seizures, reduced levels of consciousness, and hypoventilation just to name a few symptoms (Prüss et al. 2015).The treatment of this disease is a regiment of cortisone, which suppresses the immune response until the body recovered. Most patients respond so well that they can lead a normal life. Had the keepers known about this disease, they could have possibly saved Knut. This work has raised awareness that this disease is found in other animals and is not unique to humans. By raising awareness from this study, it is clear that other wild animals can suffer from this disease. It gives other animals with this autoimmune disorder a better chance at survival.

See — Prüss H, Leubner J, Wenke N, Czirják G, Szentiks C, and Greenwood A. 2015. Anti-NMDA Receptor Encephalitis in the Polar Bear (Ursus maritimus) Knut. Scientific Reports (5) DOI: 10.1038/srep12805

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