Knut's Killer: Brain Disease

An exhaustive look into the cause of death of beloved polar bear Knut, almost three years after his death, has confirmed that a viral form of encephalitis, or a brain-inflammation disease, led to his seizures and eventual drowning. "But as there were no signs of disease beforehand there was no clinical checkup," a researcher tells LiveScience. "And therefore nobody could have known for sure before the histology that there was an inflammation." The disease was caused by either an unknown virus or an eliminated infection; flu and equine herpesviruses, which have been known to wreak havoc in some zoos, were ruled out. (More polar bear stories.)