Polar bears enjoy long life; they can live up to 20 years. But the sudden death of four-year-old famous Berlin Zoo polar bear, Knut, left his fans and researchers shocked. Researchers in Germany have finally come to know that Knut died of encephalitis.

In March 2011, Knut died after suffering from seizure and collapsed into his enclosure's pool. At that time, hundreds of visitors were at the Berlin Zoo to see him. His short life was a shock and it became important to know the reason, so that the incident does not get repeated with another.

Alex Greenwood of the Leibniz Institute for Zoo and Wildlife Research said that necropsy established that Knut suffered from encephalitis, a swelling of the brain. Alex said that they were thinking of every possible option in the starting of the research.

Then, Harald Pruess, a neurologist at Berlin's Charite hospital, contacted Alex. Harald shared that while going through Knut's case, he has noticed certain similarities to some of his human patients who have suffered from anti- NMDA receptor encephalitis.

It is only eight years back that the autoimmune disease has been discovered. In the disease, body attacks his own brain cells. Greenwood said that he Knut's keepers would have known about the problem then there were chances that he would have been alive today.

Humans suffering from this condition are given cortisone. And, in most of the cases they have are able to lead normal life and there are some cases that report memory problems and difficult concentration.