A mysterious symptom complex that has appeared sporadically in young black bears in the Tahoe Basin in recent years has now appeared in two underweight young people found in northern California in the past five weeks.
The sick young men, both sacrificed and with brain inflammation, or encephalitis, were found about 15 miles away in eastern Humboldt County and across the county line in Trinity County in late February and early March.
A third bear, perhaps a brother, was observed in the same area on Wednesday, exhibiting similar symptoms, although it has not yet been captured, said Monte Merrick, director of the Humboldt Wildlife Care Center near Arcata, which received the first two.
The animals were the first known cases outside the Tahoe area to exhibit common symptoms, mainly encephalitis, documented since 2014, when the Nevada Department of Wildlife raised the red flag for the first time on young bears with neurological abnormalities in the region, said the authorities.
Less than 20 cases on both sides of the state border have since been examined, most of them in the Tahoe Basin, which has a large population of black bears and ample opportunity for human encounters, experts said.
But the pace of discoveries has increased in the past 1 ½ years, partly, perhaps, because “we are really looking,” said Brandon Munk, senior wildlife veterinarian at the California Department of Wildlife’s Wildlife Research Laboratory in Rancho Cordova, where he started in 2016.
“As soon as you start looking, you start to find,” said Munk. “To sum up the story, we really don’t have a baseline to say how prevalent this has been.”
Most afflicted bears are about half or a third the size they should have been a year old – although not so much below the size of those who passed through Humboldt County. Many have a strange gait or head tilt, tremors or other neurological symptoms, as well as monotonous and indifferent behavior or fearless “dog” behavior towards people.
Researchers increasingly focused on the problem have discovered five previously unknown and unidentified viruses in tissue samples from some of these bears, as well as others available for various reasons. Two of the five viruses have been widespread.
The type of inflammation is suggestive of a virus, said Munk, although scientists are a long way from linking symptoms to a specific source and have not ruled out other causes. It is also unknown whether the bears suppressed the immune system for other reasons and then succumbed to viruses or diseases that would otherwise not be fatal, or whether their cases are only appearing now due to increased human interaction with wildlife. .
“This may be related to urbanization, but at the same time, there may be bears in the wild who have had this and we just haven’t seen them,” said Sanchez, of the Nevada Department of Wildlife.
Denise Upton, director of animal care at Lake Tahoe Wildlife Care in South Lake Tahoe, said that animals with the syndrome remain rare, but it is sometimes difficult to say why humans are so negligent about leaving out trash and other attractions or even feed the bears directly as they become accustomed to people.
In the meantime, his organization has been treating and releasing more and more severely underweight puppies, still young enough to be with their mothers, but who were not, for some reason. Those animals, including four at the beginning of last year, who have clearly been free all winter, but who have shown no neurological deficits or other significant problems, said Upton.
“We don’t know what happens in the forest,” said Upton. But a hungry puppy that sees a person “will not show fear because hunger overcomes fear”.
“My question is, ‘What’s going on with all your mothers?’ ” she said.
The two bears captured by the Humboldt County wildlife center were found roaming close to neighborhoods in Willow Creek and Salyer, about 260 miles north of Santa Rosa, said Merrick.
Both were about a quarter and an eighth of the expected weight for their age – about a year old – with acute skin conditions, Munk said.
The female, captured on February 27 at just 5 pounds – the size a puppy would normally have been before she was even weaned, Merrick said – was initially considered for rehabilitation at Sonoma County Wildlife Rescue, one of three licensed wildlife rehabilitation centers by the state. Then Munk took a look at a picture of her.
“I said, ‘Eeeeeee. I know what that is, and it has a bad prognosis’ ”, he recalled.
The animal was transferred to the research laboratory and was later found to have mild encephalitis, although observation of it before being euthanized did not reveal any external signs of neurological problems, said Munk.