Squirrels: A New Strain of Bornavirus Detected in Europe

  A new type of bornavirus, isolated from a multicolored squirrel, is potentially linked to three fatal cases of encephalitis among owners of exotic pets in Germany. These atypical cases raise the question of a potential emerging threat in the European Union.   Three fatal cases of acute encephalitis have been reported among three German breeders of variegated squirrels (Sciurus variegatoides). These cases are likely linked to infection with a newly identified type of bornavirus.   During the prodromal phase, the three men experienced fever, chills, fatigue, and difficulty walking. As their confusion and psychomotor disturbances worsened, they were admitted to a neurology ward, where they developed ocular paresis. Their condition deteriorated rapidly, and they died after a few days in intensive care. No traces of known pathogens were detected in the cerebrospinal fluid or brain tissue samples from the deceased farmers. The Friedrich Loeffler Institute examined the carcass of a squirrel belonging to one of them. Genetic analysis, conducted using a metagenomic approach, yielded sequences of a new type of bornavirus. Molecular and immunohistochemical analyses of brain tissue from the three deceased patients confirmed the presence of this same virus in the human cases as well.   The identified virus differs from all known bornaviruses to date . Unresolved cases of encephalitis are being reevaluated in light of the discovery of this new zoonotic agent. Test results from a breeder and a zoo revealed no other animals positive for this infection, but further testing is ongoing. Tissue and cerebrospinal fluid collections from biobanks are being examined to identify additional cases. Breeders and owners of multicolored squirrels will be surveyed about the animals’ health status and any other fatal cases they are aware of. In addition, breeders are being asked to send their dead animals to the Friedrich Loeffler Institute for analysis.   At this time, the zoonotic risk cannot be assessed due to the small number of reported cases, the lack of information on the new virus, its route of transmission, its natural hosts, the prevalence of the infection in the squirrel population—it is unclear whether squirrels are a reservoir or a vector of the disease. Pending the results of ongoing investigations to characterize the cases, it is nevertheless advisable to avoid any contact with multicolored squirrels, whether alive or dead, as a precautionary measure.   Multicolored squirrels were only recently introduced to Europe. Native to Central America, they were either imported while already carrying the infection or became infected in Germany through contact with other infected animals. While the route of transmission for the three human cases has not yet been determined, it is likely through bites or scratches. However, airborne transmission—which has been observed with hantaviruses—cannot be ruled out.