California veterinarians say encephalitis is striking black bears in the Sierra Nevada and they don't know how it's happening.
In the past 12 months, officials have captured four bears with the illness, which showed them to have dangerously inflamed brains.
A side effect of the inflammation lowers the bears fear of humans...one sickly, confused female bear that was captured last fall in Pollock Pines showed no fear of people that began feeding it.
That bear was covered in ticks and because it was so ill, veterinarians had to put it down.
The only upside is that officials say black bears are not endangered and whatever has been afflicting them is not harming their population.