Dr. Brandon Munk, the California Department of Fish and Wildlife (CDFW) Senior Wildlife Veterinarian spoke with CBS News about the mystery illness in bears.
“Someone opened the trunk and it climbed in the trunk and that is not normal behavior. And that’s got to be a red flag right? That’s got to be a red flag that something is not right.”
In California, there have already been four cases seen this year in several counties including El Dorado and Tulare, with the latest case turning up Thursday, last week in a young bear in Humboldt County.
One case, in Pollock Pines, El Dorado County, exemplifies the condition most of the afflicted bears seem to have. According to CDFW, “a small, black bear showed up at a utility worksite. It was alone and possibly sick – lethargic and showing little fear of people. The bear was largely unfazed by attempts to shoo it away by yelling and clapping.”
When CDFW went to investigate, “they encountered a situation becoming more common in the Tahoe Basin and elsewhere around the state. They found a bear too young to be out on its own, “dog-like” in its behavior, completely comfortable around people, picking up an apple to eat in front of them on the backyard patio. Physically and mentally, the bear just didn’t seem quite right, walking oddly, dull and not responsive like a normal bear should be.”
The young bear was taken to CDFW’s Wildlife Investigations Laboratory (WIL) in Rancho Cordova. There, veterinarians found the yearling female covered in ticks and weighing only 21 pounds. A typical weight for a yearling is 80 pounds. Under observation for a week, the bear displayed intermittent head tremors and a subtle head tilt, troubling signs of neurological abnormalities.
The bear’s condition continued to deteriorate and the animal was euthanized and a post-mortem was done. Preliminary findings have confirmed encephalitis or inflammation of the brain. And while necropsies on the afflicted bears have confirmed encephalitis, the root cause of the disease remains a mystery.
Unexplained encephalitis cases in American black bears
Dr. Munk has been studying the strange behavior in bears since the first case popped up in 2014 in Nevada. The Nevada Department of Wildlife had growing concerns over encounters with young black bears with neurological abnormalities in the Tahoe Basin.
Dr. Monk collaborated with other veterinarians and wildlife specialists in a study of the viral infections being seen in American black bears (Ursus americanus) from Nevada and northern California with and without idiopathic encephalitis. The research was published in the journal PLOS One in December 2020.
Analyses of tissue pools revealed five novel viruses in the genera Circoviridae, Parvoviridae, Anelloviridae, Polyomaviridae, and Papillomaviridae. The circovirus and parvovirus were of particular interest due to their potential importance as pathogens.
Given their pathogenicity, the two novel viruses were further investigated for prevalence using PCR. Polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it to a large enough amount to study in detail.
As it turned out, “the novel circovirus was detected at a high prevalence and was further evaluated for tissue distribution and possible lesion association by in situ hybridization (ISH),” according to the study. The new circovirus has been given the name: Ursus americanus circovirus (UaCV) genome (GenBank accession MN371255).
The new circovirus found in black bears is most similar to a circovirus identified in a masked palm civet, a species native to the Indian subcontinent and Southeast Asia. Needless to say, but Ursus americanus circovirus shares 75.42% nt sequence identity with the civet virus.
As the study notes, there is no evidence to suggest a recent viral spillover from palm civet to black bear; rather, the researchers speculate that UaCV has been enzootic but previously undetected in black bears.
A clear relationship between infection status and neurologic lesions was not established for any of these viruses. However, this study expands the known diversity of viruses infecting free-ranging black bears in North America, while a few of the identified viruses warrant further investigation as potential pathogens.
