Three people in Germany who worked as squirrel breeders and who all died from brain inflammation may have contracted a new strain of virus from their squirrels, according to a new report of the cases.
The new virus strain belongs to a group of viruses called bornaviruses, which typically infect animals such as horses, sheep and birds. Researchers have debated whether this group of viruses can cause disease in people.
The new findings suggest such viruses do cause disease, and moreover, raise the question of whether this virus "represents an emerging threat" to people in the area, according to a recent statement from the European Centre for Disease Prevention and Control.
The three squirrel breeders who died were all men in their 60s and 70s. They were friends with each other and met on a regular basis. They bred variegated squirrels, which are sometimes kept as exotic pets. At least two of the men had experienced scratches and bites from their squirrels, the report said.
Between 2011 and 2013, all three men developed encephalitis, which is inflammation in the brain, and is usually caused by a virus. They experienced fever, chills and weakness, and later, confusion and difficulty walking. All three men were hospitalized and treated in intensive care units, but each eventually went into a coma and died within two to four months of their first symptoms, the report said.
Tests for the usual causes of encephalitis did not initially reveal the culprit. But a more detailed genetic test of one of the squirrels owned by the breeders identified a new type of bornavirus, which the researchers call VSBV-1.
Further study identified this virus in the brain tissue of all three patients, and antibodies to the virus were found in the blood and spinal fluid of one of the men, pointing to the virus as the likely cause of the men's fatal brain inflammation, the researchers said.
"VSBV-1 is likely to be a previously unknown zoonotic pathogen transmitted by the variegated squirrel," the researchers, from the Friedrich Loeffler Institute in Germany, wrote in the July 9 issue of the New England Journal of Medicine. [10 Deadly Diseases That Hopped Across Species]
However, the new study does not definitively prove that this virus caused the encephalitis, the researchers noted.
Still, until more research is done, "feeding or direct contact with living or dead variegated squirrels should be avoided as a precautionary measure," the ECDC said.
Many questions remain, including where the virus naturally "lives" and how it is transmitted. In addition, people with unexplained encephalitis could also be tested for the virus, the researchers said.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.