Researchers from the universities of Regensburg, Munich, Giessen, and Freiburg, the Bernhard Nocht Institute for Tropical Medicine in Hamburg and the Friedrich-Loeffler-Institut (FLI) provided new insights into human infections with Borna Disease Virus (BoDV-1) in a new study published in the Lancet Infectious Diseases this week.

Image by Ralph Häusler from Pixabay

BoDV-1, which has long been known as the causative agent of Borna disease in horses, sheep and other mammals, was first identified as the cause of severe human encephalitis in 2018. Within the framework of the current study published by the FLI and the University of Regensburg, presence of the virus could be confirmed in current as well as in archived cases. The most recent known case occurred at the end of 2019.

So far, 14 cases have been detected in Bavaria between 1999 and 2019.

The reservoir of the pathogen is the bicolored white-toothed shrew. According to the study, infection through contact with an infected bicolored white-toothed shrew or its excrements can be assumed in the majority of cases. However, the exact transmission route is still unknown. Natural human-to-human, horse-to-horse, or horse-to-human transmission can be ruled out according to current knowledge.

The results of the cooperating research groups and treating physicians in the surrounding hospitals in Bavaria make it clear that BoDV-1 is a virus with a very high death rate. However, the absolute number of infections and hence the risk of infection is estimated to be very low. An increase in the number of cases in recent years has not been observed. However, it is unclear whether there are more cases that have not yet been diagnosed.

In order to create a better data situation regarding the occurrence of human infections, compulsory notification of BoDV-1 infections will be introduced in March of this year in Germany.

BoDV-1 infection has to be considered as a potentially lethal zoonosis in endemic regions with reported spillover infections in horses and sheep. BoDV-1 infection can result in fatal encephalitis in immunocompromised and apparently healthy people. Consequently, all severe encephalitis cases of unclear cause should be tested for bornaviruses especially in endemic regions.

The main risk areas are Bavaria, Thuringia, Saxony-Anhalt as well as parts of adjoining federal states.