It’s Not Just for Humans Anymore

By Colleen Murphy

Her favorite animal is the polar bear, but one polar bear in particular – Knut. This little girl lives in Berlin, and her favorite place in the whole entire world is the Berlin Zoological Garden because that is where Knut lives. She remembers the first time she saw Knut at the zoo: his area was crowded with reporters, and at first she did not understand why so many people with cameras were focusing on this one animal. She worked her way to the front where all the cameras were to see this new animal at the zoo. When she looked into the habitat, she saw a bundle of white fur that was exploring like crazy. After that day, she was hooked on Knut the polar bear. Every time she went with her family to the zoo they always had to say hello to Knut first, and before they left they had to say goodbye to him. She had her own plushy Knut bear along with several books on polar bears. She even learned Knut’s scientific name – Ursus maritimus.

But something about Knut was starting to change. She began to notice that Knut was making funny movements just before a zoo worker would ask onlookers to leave the exhibit for a different part of the zoo, but other times Knut seemed just fine. Then on March 19, 2011 she cried for a whole day because her beloved polar bear Knut had died.

Video Citation: Uzoo, YouTube

This is what I imagine children all over Berlin, maybe even from farther places, felt like after the death of Knut. The cause of Knut’s death was drowning because while suffering from an epileptic seizure he fell into a pool in his habitat. However, the story of Knut did not end with his death. After a pathological analyses, scientists determined that Knut’s seizures were caused by encephalitis. Following the encephalitis diagnosis, an in-depth analysis comprised of multiple tests concluded that the cause of infection was an unknown pathogen. The proper name of the diagnosis was “encephalitis unknown etiology,” which is a fancy way of saying, “we have no idea what caused this inflammation in your brain.”

While Knut’s case seemed to be an anomaly, there was one neurologist who saw a connection. Dr. Harold Pruess is a specialist in neurology who researches human brain diseases at the German Center for Neurodegenerative Diseases (DZNE) in Berlin. After reading the autopsy report on Knut, Pruess noticed characteristics that he had found in his own research from humans. In order for Pruess to draw any concrete conclusion he needed a way to analyze samples of Knut’s brain. So Pruess partnered with the leader of the Department of Wildlife Diseases at the Leibniz Institute for Zoo and Wildlife Research (IZW), Professor Alex Greenwood.  Greenwood and Pruess were able to procure the brain tissues needed for the study from the IZW, and the analysis revealed Knut the polar bear had suffered from anti-NMDA receptor encephalitis.

Anti-NMDA receptor encephalitis is an autoimmune disease where the body malfunctions and creates antibodies programmed to damage nerve cells rather than to fight against pathogens. The disease was only identified in humans in 2010, but since its identification it has become treatable. Knut is the first reported non-human case of anti-receptor encephalitis in wild or domestic animals. Before Knut, this disease was only recognized in humans, but by using the diagnostic criteria for humans it was determined that Knut suffered from anti-NMDA receptor encephalitis. In the study published in Science Reports, the criteria for diagnosis were described as the following:

  1. clinical signs of encephalitis such as epileptic seizures, lack of consciousness, and cognitive or mood changes
  2. indication of brain inflammation from MRI abnormalities or positive biopsy/autopsy
  3. no possibility of viral or bacterial causes
  4. the presence of NMDAR antibodies

Knut had a history of seizures, observed inflammation in the brain, no detectable of viral or bacterial sources of infection, and very elevated levels of NMDAR antibodies. All of these results confirmed the post-death diagnosis of anti-NMDAR encephalitis in Knut. The diagnosis of this disease in Knut means two important conclusions for the world of zoological medicine. First, if anti-NMDAR encephalitis was present in Knut then the disease could be common in many mammals. Second, there could be other forms of autoimmune encephalitis that have been identified in humans but that have yet to be discovered in wild mammals as well.

Even though Knut was only able to enjoy his polar bear popularity for a short time, he has become part of a major study in neurology. His case and diagnosis may help wild mammals everywhere.

Photo Credit: Marmontel, Flickr

Photo Credit: Marmontel, Flickr


Prüss, H. et al. Anti-NMDA Receptor Encephalitis in the Polar Bear (Ursus maritimus) Knut. Sci. Rep. 5, 12805; doi: 10.1038/srep12805 (2015).

DZNE – German Center for Neurodegenerative Diseases. “Mystery of polar bear Knut’s disease finally solved: The animal suffered from an autoimmune disease previously known only in humans.” ScienceDaily. ScienceDaily, 27 August 2015. <>.


Update 9/16/2015: Edited by Paige Jarreau


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