Information from the FLI on the current situation with Bornaviruses
Bornaviruses (family Bornaviridae) play a role in veterinary medicine as causative agents of severe to fatal neurological diseases in mammals and birds. This includes above all the "Borna disease" in domestic mammals caused by the Borna disease virus 1 (BoDV-1). In addition, both BoDV-1 and variegated squirrel bornavirus 1 (VSBV-1), a species found in exotic squirrels, have great zoonotic potential and can cause fatal encephalitis in humans.
Borna virus infections in mammals have been notifiable since March 31, 2020.
Borna disease virus 1 (BoDV-1)
Borna disease caused by BoDV-1 is the result of an immune-mediated, non-purulent encephalitis. Diseased animals show a wide range of neurological symptoms, such as ataxia, circular movements, idle chewing or blindness. It is most commonly diagnosed in equidae (horses, donkeys), sheep and New World camelids (alpacas, llamas), but other domestic mammals are also susceptible. Coruses of the disease in humans are similar to those in animals. They are extremely rare, but have been fatal in almost all cases known to date.
The so far known reservoir of BoDV-1 is the bicolored white-toothed shrew (Crocidura leucodon), which does not develope disease upon BoDV-1 infection, but excretes the virus via feces, saliva and urine. Infected domestic mammals and humans, on the other hand, do not excrete the virus. The occurrence of the virus is largely limited to areas in southern and eastern Germany as well as Austria, Liechtenstein and Switzerland (see map of risk areas).
The closest relative of BoDV-1 is Borna disease virus 2 (BoDV-2), which has so far only been detected in a single horse that died of Borna disease in Styria, Austria.
Variegated squirrel bornavirus 1 (VSBV-1)
VSBV-1, which has only been known since 2015, occurs in holdings of exotic squirrels, particularly Prevost´s squirrels (Callosciurus prevostii) and variegated squirrels (Sciurus variegatoides). In Germany it was detected in nine holdings until 2017, but since then only in a single case in 2019. The origin of VSBV-1 is not yet known. It has not been detected in native red squirrels (Sciurus vulgaris).
Infected squirrels excrete the virus without becoming ill themselves. However, after transmission of the virus to humans, severe immune-mediated encephalitis occurs which resembles BoDV-1-induced disease. Four of the five known cases have been fatal.
Bornaviruses in birds, reptiles and fish
The group of parrot bornaviruses (parrot bornavirus 1 to 8, PaBV-1 to -8) has the greatest veterinary significance among the bornaviruses known from other animals. They are causative agents of the proventricular dilatation disease (PDD), which is widespread in parrots and parakeets. In addition, bornaviruses also occur in canaries, estrildid finches and wild waterfowl. However, little is known about their pathogenic potential. The same applies to the bornaviruses discovered in snakes and fish.
Bornavirus diagnostics & reporting obligation
The most suitable diagnostic procedure depends on the virus in question and the host to be examined.
In infected reservoir hosts (shrews for BoDV-1, squirrels for VSBV-1), the virus can be detected in the excretions (e.g. oral swabs, faecal samples) and in many organs, with the highest viral load mostly being found in the brain.
In the case of non-reservoir hosts (e.g. horses, sheep, alpacas for BoDV-1, humans for BoDV-1 & VSBV-1) intra vitam diagnosis is much more challenging, since the viruses are almost completely restricted to the central nervous system. Large amounts of virus can therefore only be detected in the brain, eye and spinal cord. Low amounts are occasionally found in peripheral nerves or in the cerebrospinal fluid, but not in blood or excretions (e.g. mucosal swabs).
The serological detection of antibodies against bornaviruses is possible and can provide important information about an infection. However, since false positive results can also occur, serology only allows a suspected diagnosis, which must be confirmed by direct virus detection.
Direct evidence of a bornavirus infection in a mammal is notifiable in Germany. The notification does not entail any animal health measures.