Variegated Squirrel 1 Bornavirus First Described in Germany
Last week, the New England Journal of Medicine published an article regarding a novel zoonotic disease, first described as the suspected cause of three fatalities in Germany (1). The new virus, which has been provisionally termed ‘variegated squirrel 1 bornavirus’ or VSBV-1, was found to be unique from the previously known and described bornaviruses (1). VSBV-1 was tentatively named for its first cases: three men from the Saxony-Anhalt region of Germany who bred variegated squirrels (Sciurus variegatoides) (1, 2, 3). The particular species of squirrel common across all of the breeders, variegated squirrels, originates in parts of Central and North America and were kept as exotic pets (3).
In 2015, German officials reported a cluster of three acute fatal encephalitis cases in the Saxony-Anhalt region to the Early Warning and Response System of the European Center for Disease Control (ECDC) (4). The cases occurred in succession between 2011 and 2013, with deaths occurring 2-4 months after symptom onset, despite thorough anti-infective treatment (1). The three men first presented with neurologic symptoms ranging from fatigue, confusion, psychomotor slowing, headache and/or fever (1). The cases’ conditions deteriorated rapidly after hospital admission, eventually requiring intensive care treatment and mechanical ventilation (4). All cases were comatose at time of death at their respective hospitals (4).
The three initial cases were also friends, belonged to the same squirrel-breeding association, and had a history of exchanging breeding stock (3-4). Researchers theorize that the men’s route of exposure were reported histories of being scratched or bitten by their squirrels (1). Due to the time lapse between the cases, the first case occurring more than a year before the second and third cases, human-to-human transmission is unlikely, but cannot be entirely ruled out (4). The ECDC report on the case cluster details the possible explanations for the time occurring between cases (4).
Due to the fact that this would be a first incidence of a previously unknown disease, there is no definitive method of testing for VSBV-1, or for Borna disease viruses in humans. Researchers cannot say for certain that VSBV-1 was the etiologic source of the three acute fatal encephalitis cases. However, the clinical similarities of the cases, and pathologic similarities to one of the pet variegated squirrels, suggest it was the ‘likely causative agent’ (1).
Borna Disease Virus
The novel VSBV-1 was found to be a phylogenetically unique lineage from previously described Borna disease viruses (1). Never heard of Borna disease virus (BDV) before? You’re not alone.
BDV has been found to have co-existed with primates for approximately the past 40 million years (5). It was first described as the causative agent of a neurologic disease outbreak among horses in the German town of Borna in the 1800s (4, 8). It has since been recognized as an often-fatal disease affecting a range of livestock and domestic animals (5). BDV is a single stranded RNA virus that preferentially invades the central nervous system – leading to cognitive changes and encephalopathy (6-7).
Due to the virus’ propensity to affect the central nervous system, and because it has been characterized by ‘behavioral abnormality and movement disorders in laboratory rodents’ (6), researchers have surmised possible links between human infection and mental/mood disorders (5). This connection remains controversial, despite growing research on the topic, due to disparities in study and serologic testing methods (5).
VSBV-1 Next Steps
The New England Journal of Medicine article and the ECDC report describing the cluster of squirrel-breeder encephalitis deaths highlight a need for more research before making generalizations and recommendations. Both reports indicate the need for further studies on potential reservoirs and cases in humans (1, 4). The ECDC report indicates that other variegated squirrel breeders may be at increased risk, and suggests the general public avoid direct contact with the particular species of squirrel (4).
Emerging or novel infectious diseases may seem uncommon, but they happen more than you think. Up to 75 percent of emerging infectious diseases in humans have animal origins (9).
Researchers are uncertain where the variegated squirrel breeding stock, that passed the virus to the three men, contracted VSBV-1. It is possible that the squirrels became infected locally, in Germany, or prior to their importation (1, 3, 4). Only further research will reveal the who/what/where are most at risk of the newly described Borna disease virus, VSBV-1.