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Those “Friendly” Bears Are Suffering From Brain Disorder

Scientists Are Tracking Down the Cause of Neurological Disorders in Black Bears


Some of the bears appeared lethargic and were unfazed by human activity around them, while others were described as “dog-like” in behavior, approaching people on a ski hill, or hanging out in a yard while being fed treats from the neighborhood. But a closer look at these black bears that seemed comfortable around humans revealed startling symptoms of a neurological disorder: odd head-tilting, tremors, and an unsteadiness on their feet.


The Nevada Department of Wildlife sent out a warning to California wildlife colleagues back in 2014 that it was seeing a growing number of bears with neurological abnormalities in the Tahoe Basin. Last week, the California Department of Fish & Wildlife announced that researchers had confirmed at least four black bears suffering from encephalitis, or inflammation of the brain, within the last 12 months.


“Necropsies on the afflicted bears have confirmed encephalitis but the root cause of the disease remains a mystery,” according to a statement from CDF&W. “During their investigations into the cause, scientists have discovered five novel viruses – previously unknown and unidentified – though their relationship to the condition and the neurological disorders remain unknown.”


Researchers examining 17 black bears originating in California and Nevada from 2014 to 2019 found brain lesions that “were suggestive of viral etiologies” according to a new research paper. That research led to the discovery of five new viruses, and “Of these, the circovirus and parvovirus were considered plausible causes of the observed neurologic lesions based on patterns of disease recognized in other species.”


The circovirus (now named Ursus americanus circovirus) was detected in 67% of the bears (10 of 16), while the parvovirus (named Ursus americanus parvovirus) was detected in a single bear.


“A clear relationship between the infection status and neurologic lesions was not established for any of these viruses,” the researchers concluded, while noting that “several of the identified viruses warrant further investigation as potential pathogens.”

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