We Now Know What Killed the Polar Bear Knut

It was less than a decade ago that Knut came into our lives, stole our hearts with his adorable self and became a media phenomenon spawning soft toys, books and songs. Four years later, on March 19th, 2011, he collapsed and died, leaving the world heartbroken. We now know what caused his death.

An autoimmune disorder caused Knut to die

Knut died after having a seizure, which caused him to collapse in the pool within his enclosure. It was known at that time that he suffered from encephalitis⎯an acute inflammation of the brain that could have serious consequences if left untreated. While Knut’s encephalitis was previously thought to be bacterial or viral in origin, we now know that an anti-NMDA receptor encephalitis caused his demise. This is an autoimmune condition that, until recently, was thought to affect only humans. In this condition, the body’s immune system attacks and destroys its own organs.

Scientists at the German Center for Neurodegenerative Diseases (DZNE), the Leibniz Institute for Zoo and Wildlife Research (IZW) and the Charite Universitaetsmedizin Berlin collaborated to solve this case. They examined the autopsy reports and the preserved brain samples and realized that the disease was similar to autoimmune brain diseases seen in humans. Brain samples revealed antibodies to the NMDA receptor, indicating an attack by Knut’s own immune system. Since very little was known about the autoimmune origin of encephalitis (only now have diagnostic tests been developed for humans), Knut’s diagnosis was implausible at the time of his death. Today, once the bacterial and viral reasons are ruled out, the anti-NMDA receptor autoimmune condition is checked for as the next likely candidate in diagnosing encephalitis. Solving Knut’s case brought the similarities between the human and animal manifestations of this disorder to light.

What this means for animal welfare

This confirmed diagnosis of Knut’s death puts to rest rumors about the zoo’s negligence and the resultant stress on Knut’s system. Thanks to this finding, autoimmune encephalitis is now known to commonly affect members of the animal kingdom. So, veterinarians can look for signs of this disorder and add immune-suppressing drugs⎯drugs used to treat autoimmune conditions in humans⎯to the animal treatment protocol.

Photo Credit: Knut. via photopin (license)

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