Bornavirus explained: origin, transmission, symptoms & protection
The Bornavirus is largely unknown in Germany, although it can cause severe brain inflammation ( encephalitis ) in humans, which is usually fatal. For a long time, the virus was considered a purely animal disease. However, since 2018, it has been proven that humans can also become infected – especially in certain regions of southern Germany. Most recently, a man from Bavaria died from the consequences of the infection in June 2025.
Where the virus occurs, who is particularly at risk – and what protective measures are possible.
Bornavirus is a neurotropic virus – it specifically infects nerve cells in the central nervous system. It belongs to the Bornaviridae family and occurs in several genetic variants. The most relevant strain for humans is Borna Disease Virus 1 (BoDV-1) , which was originally discovered in horses but can also infect other animals.
BoDV-1 causes severe neurological diseases and can also trigger usually fatal encephalitis in humans. This transmissibility has been scientifically proven since 2018.
The European shrew is considered the primary natural host of the Bornavirus. The virus can multiply continuously in its body without the animal itself showing symptoms—it thus serves as a so-called reservoir, a permanent ecological source of the pathogen.
Field shrews do not belong to the rodents, but rather insectivores. They are smaller, have sharper faces and smaller eyes and ears than real mice.
Source: IMAGO/blickwinkel
Field shrews live primarily in rural areas , gardens , forests , and forest edges . They are crepuscular and nocturnal and feed primarily on insects. Their habitats often overlap with those of domestic cats and humans – for example, on farms or in villages.
The transmission probably occurs through:
- Contact with virus-containing feces , urine or saliva
- contaminated soil , dust or feed
- possibly also by inhaling infectious particles from the environment
Important: The common shrew does not have to be sick to transmit the virus. Once infected, it can shed the virus continuously—thus contaminating its environment for the long term.
While the common shrew, as a natural host, carries the virus asymptomatically, there are a number of so-called accidental hosts : animals that become infected but in which the virus causes severe illness and is not spread further. These include:
- horses
- sheep
- domestic cats
- Alpacas and llamas
- occasionally wild animals such as deer or foxes
In these animals, the disease is usually acute and severe: they develop sudden changes in behavior, coordination disorders, loss of appetite and neurological deficits – in many cases the infection is fatal.
Cats are considered so-called accidental hosts: They can become infected with BoDV-1 and exhibit severe neurological symptoms. However, the virus cannot be transmitted to humans via cats because they do not excrete the virus.
Cats can act as virus carriers after hunting or eating shrews - owners should be careful here.
Source: Peter Endig/dpa-Zentralbild/dpa
However, there is an indirect risk of infection : Cats that catch infected shrews can carry virus-containing bodily fluids such as blood or saliva on their fur, mouths, or paws. Therefore, especially in high-risk areas, cats should be prevented from accessing shrews—for example, by closing cat doors.
Yes, since 2018, it has been scientifically proven that BoDV-1 can also cause infection in humans. According to the Robert Koch Institute (RKI), it particularly affects the brain and leads to a severe, usually fatal inflammation known as encephalitis .
So far, the reported cases come almost exclusively from certain regions in southern and eastern Germany, including:
- Bavaria
- Thuringia
- Saxony
- Saxony-Anhalt
- Northeast Baden-Württemberg
Individual cases have also been documented in Austria , Liechtenstein , and Switzerland . However, the disease can occur throughout Germany.
The exact mode of transmission has not yet been conclusively determined, but is considered predominantly indirect. The following mechanisms are considered likely:
- Indirect contact with excretions of infected shrews, for example via soil, stable dust or feed
- Contact with contaminated surfaces (e.g. through gardening, stable cleaning)
- Contamination via hands, objects or clothing
- Inhalation of virus-containing particles (e.g. dust in barns)
Direct human-to-human transmission has not yet been proven. The risk of transmission through blood transfusions or organ transplants is also considered extremely low, but cannot be completely ruled out under certain circumstances.
Infection with the Bornavirus usually progresses slowly, but almost always develops dramatically and is often fatal.
Early phase:
- Fever
- Headaches and body aches
- fatigue
- Nausea, vomiting
- Difficulty concentrating
Advanced phase:
- Speech and memory disorders
- Unsteady gait, paralysis
- Hallucinations, confusion
- Seizures
- Unconsciousness, coma
After the first symptoms appear, if left untreated the disease leads to death within a few weeks.
Diagnosis is challenging due to nonspecific symptoms and the rare occurrence of the disease, and is often only performed in advanced stages. The following tests are used:
- MRI of the brain to detect inflammatory changes
- Lumbar puncture (cerebrospinal fluid analysis) to search for signs of inflammation and viral material
- PCR tests for viral RNA (e.g. from cerebrospinal fluid or brain tissue)
- Detection of antibodies in blood or cerebrospinal fluid (CSF)
There is currently no reliable early detection method.
To date, there is no approved antiviral therapy against BoDV-1, and a vaccine is not in sight . Experimental treatment approaches have so far shown no proven success.
Medical care is therefore limited to intensive care measures and symptom control.
In endemic areas, certain rules of conduct should be observed to minimize the risk of infection:
- Avoid contact with shrews (live or dead)
- Never touch shrews with bare hands
- Carry out gardening and forestry work with gloves and respiratory protection
- Clean and ventilate cellars, sheds, and stables regularly
- Treat contaminated surfaces with disinfectant
- Do not allow domestic cats access to shrew territories
rnd
