Bornavirus in Germany: Symptoms, infection, prevention

For a long time, it was assumed that Bornavirus was a purely animal disease—that is, it only affected farm animals, such as sheep and horses. However, in 2018, it was demonstrated for the first time that the virus can also, in rare cases, cause severe encephalitis in humans. Recently, another human died as a result.

Two people in this country recently became infected with the Borna virus. The cases were discovered in early June 2025 in the urban area of ​​Pfaffenhofen, a town of approximately 30,000 inhabitants in Upper Bavaria. According to local authorities, one person has died as a result, and one is receiving medical treatment (as of June 2, 2025).

The virus has long been known to cause severe encephalitis in horses, sheep, and mammals in Central Europe. In 2018, it was first identified as a cause of severe encephalitis in humans—and only in Germany. However, experts assume that undetected transmissions have occurred earlier. The pathogen is also known as Borna Disease Virus 1 (BoDV-1). According to the Robert Koch Institute (RKI), endemic areas in Germany are primarily Bavaria, Saxony-Anhalt, and parts of Brandenburg and Thuringia.

Most human infections discovered so far have occurred in rural Bavaria. No human cases have been detected in other states. However, it is likely that this could occur anywhere where the virus is present in field shrew populations and spreads to mammals.

The Robert Koch Institute (RKI) estimates that there are approximately five to ten acute cases of the disease in this country each year. This is one of the "rarest diseases" in Germany. By comparison, around 200 people are struck by lightning each year, and more than 2,000 die in traffic accidents. "It is not expected that there will be more BoDV-1 cases in Germany in the future than there have been so far," the RKI concludes.

According to current research, BoDV-1 is transmitted from field shrews to mammals and humans. Despite surveys, the exact route of transmission—that is, how and where humans encountered the shrew—is unknown. "Based on current knowledge, the greatest probability of infection occurs through contact with shrews or their excrement," says the Robert Koch Institute (RKI).

The animals are rare in Central and Southeastern Europe and are mostly found in rural areas, along roadsides, stone walls, and hedges. They are insectivores. The viruses of infected animals are transmitted to the outside world via saliva, urine, and feces.

In all human cases to date, the infection has resulted in severe, life-threatening encephalitis—inflammation of the brain. The disease affects all genders and age groups. However, infants and young children have not been among the known cases.

The exact incubation period is unknown, but it is estimated to last from weeks to months. Those infected initially suffer from headaches, fever, and a general feeling of illness. Speech and gait disturbances are also typical. After a few days, infected individuals fall into a coma. In all cases reported so far, all but one patient died. There is currently no treatment for the infection. A diagnosis is only possible in the advanced stages of the disease. This can be made by the Bernhard Nocht Institute for Tropical Medicine and various university hospitals. There is no "early test."

Overall, according to the Robert Koch Institute (RKI), disease is unlikely and the risk of disease is low. However, the risk of BoDV-1 infection can be reduced, especially in endemic areas, by avoiding contact with shrews and their feces. The animals, whether dead or alive, should not be touched with hands. The mice are also not suitable as pets. Be careful: Shrews are attracted to dog and cat food, and compost heaps and waste can also attract them.