Scientists are worried about a deadly threat to bears living near Lake Tahoe.
They are investigating a mysterious and lethal condition that causes their brains to become dangerously inflamed.
The virus has a peculiar effect on the behavior of bears. They show no fear when they are around humans, according to researchers.
Several bears near Lake Tahoe have died from the disease in the past two years, scientists said.
The cause of the disease is still unknown.