Bear cubs in California are developing an unexplained illness that makes them friendly and not afraid of people

• Black bear cubs in California have been showing "dog-like" behavior, officials say.
• Officials say the behavior is on the rise and is likely linked to a brain condition.
• Scientists don't know the exact cause but have identified five viruses in the bears.

Some black bear cubs in California have been exhibiting uncharacteristic, overly friendly "dog-like" behaviors, and scientists aren't sure why.

The California Department of Fish and Wildlife said on Wednesday that last month it picked up a small female black bear with this kind of behavior from Pollock Pines, east of Sacramento.

The young bear, which was underweight, had moved into a residential backyard and was comfortable around people, picking up apples and eating them in front of the residents on their patio, the department said.

The bear did not respond to the people yelling or clapping, and at one point it jumped into a housekeeper's open car trunk, the CDFW said.

Brandon Munk, a wildlife veterinarian with the department, told CBS Sacramento that this was "not normal behavior" and was a "red flag."

The phenomenon was identified in 2014, the CDFW said.

Like other bears picked up before her, the small bear in Pollock Pines displayed a head tilt and walked oddly, the department said.

In 2019, a snowboarder captured video of a bear with this kind of behavior:

In one instance in the past few years, a bear walked into a classroom and "sat in the back just like a puppy dog," Ann Bryant, the executive director of the nonprofit Bear League, told CBS Sacramento.

Scientists have found that this behavior is linked to encephalitis, or inflammation in the brain, the CDFW said. But it wasn't clear what had caused the encephalitis.

Five new viruses have been identified in these sick bears, but scientists don't know whether they are linked to the symptoms, the department said.

The viruses don't appear to be a risk to humans, Jamie Sherman, a veterinarian at UC Davis' One Health Institute, told The Sacramento Bee.

In the past year, four bears with these symptoms have been brought to authorities, the CDFW said, adding that the situation was becoming "more common in the Tahoe Basin and elsewhere around the state."

One bear was spotted in Humboldt County, a 366-mile drive from Lake Tahoe, and some have been seen on the Nevada side of Lake Tahoe.

Bears with this neurological condition cannot survive in the wild, and some, like the young black bear who hugged the snowboarder, have been placed in wildlife care facilities and zoos, the CDFW said. The small bear picked up in Pollock Pines, however, was euthanized.