New bornavirus strain detected in the EU, 26 February 2015

Risk assessment
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European Centre for Disease Prevention and Control. New bornavirus strain detected in the EU – 25 February 2015. Stockholm: ECDC; 2015.

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​This rapid risk assessment assesses the public health threat of a recently reported cluster of acute fatal encephalitis in three squirrel breeders in Germany, possibly related to an infection with a newly identified bornavirus.
A recently reported cluster of acute fatal encephalitis in three squirrel breeders possibly related to an infection with a newly identified bornavirus is an unusual event. The novel nature of this occurrence requires that additional investigations are undertaken into the role of a new bornavirus in the aetiology of these cases, the identification of natural hosts, reservoir and the transmission route.

Nevertheless, pending the completion of the cluster investigation, it is advised that feeding or direct contact with living or dead variegated squirrels should be avoided, as a precautionary measure.

Further investigations are ongoing to characterise these cases. In addition, testing of cases of human encephalitis for this newly identified bornavirus, especially in areas where the presence of bornavirus is documented in animals, can contribute to a better understanding of the risk of bornavirus infection in humans.

Executive summary

No new cases were found during the first epidemiological investigations following the fatal encephalitis in three breeders of variegated squirrels in the German state of Saxony-Anhalt. Further laboratory testing is needed to better understand the animal-to-human transmission of the virus and its role in the said fatal encephalitis cases, states the first update of the ECDC risk assessment on Borna disease virus. There is so far no definitive evidence that the presence of Borna disease virus in the brain tissue of the three affected patients in Germany caused the encephalitis symptoms. The virus transmission – the roles of the variegated squirrels in the zoonotic transmission (whether they are reservoir or a vector), the way of its transmission from animals to humans and whether other animals can be affected, is also yet unknown. No new cases of encephalitis have been reported since the previous update of the risk assessment following the epidemiological investigations among variegated squirrels breeders in Germany.  The risk assessment conclusions remain unchanged: 

  • The three acute fatal encephalitis cases in breeders of variegated squirrel in the German state of Saxony-Anhalt is an unusual event with a potentially high impact on the small group of people who are exposed to this particular squirrel species.
  • The probability of infection for people who breed variegated squirrels or keep them as pets is higher (The variegated squirrel is an exotic species of squirrel, native to central and northern America and introduced to Europe as a pet animal.). 
  • It is recommended as precautionary measure that direct/close contact is avoided with living or dead variegated squirrels until more is known about the virus. 
  • The role of the newly identified Borna disease virus in the cases remains to be confirmed and further laboratory investigations is needed to understand better the risk of infection in humans.

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