What is Borna's disease virus?

The bronavirus BoDV-1 is the causative agent of Borna's disease. This animal disease occurs rather rarely in humans. Borna's disease is a zoonosis, i.e. an infectious disease transmitted from animals to humans . However, human-to-human transmission is considered quite unlikely. Particularly frequently infected by the virus are field shrews, as these are the natural hosts of the virus. However, horses and sheep are also considered carriers of the disease. In 2018 , the BoDV-1 was found to be causative for encephalitis in a human for the first time.

How common is Borna disease virus?

The infections with the virus are rare in humans. Only 2 people per year in Germany are infected with BoDV-1. However, assumes that the number of unreported cases is significantly higher, but still in the low two-digit range. Histological examinations of brain tissue samples from people who died of encephalitis revealed that a minimum of 14 people were infected with the virus and died from it between 1999 and 2019. So far, however, it is still completely unclear to what extent the Borna virus is behind brain infections with an unknown cause. Since March 2020, there has been a reporting obligation for Borna virus infections, which means that if the virus is detected, the responsible laboratory is obliged to report it to the public health department.

How is the Borna disease virus transmitted?

The virus spreads via the excretions of field shrews such as urine, faeces or saliva, but also via contaminated water, food and contaminated dust. But of course, the bite of a shrew can also be considered a carrier.

How is Borna disease virus spread?

The natural occurrence of Borna disease virus is limited to the regions of Germany, Austria, Switzerland and Liechtenstein, , because the field shrew, as the natural host of the pathogen, is native to these regions. In Germany, the following are considered particularly risky areas

• Baden-Württemberg,
• Bavaria,
• Thuringia,
• Saxony,
• Saxony-Anhalt.

 
The field shrew is considered to be very loyal to its location, which is why it leaves its territory only in rare cases. In view of this, infection between two species is also only rare. This in turn has the advantage that the virus can only spread very slowly.

What are the symptoms of Borna disease?

In most cases, only non-specific symptoms develop at first, such as:

• Fever,
• Headache,
• general feeling of illness.

 
After a few days, neurological symptoms often appear:

• Behavioural abnormalities,
• Speech disorders,
• Gait disorders.

 
As the bornaviruses move into the cells of the central nervous system, these complaints occur. As the disease progresses, it can lead to severe brain inflammation. Within a few days, the affected person often falls into a coma. If Borna's disease is not treated, it is fatal.

How is Borna's disease diagnosed?

If you notice the above-mentioned symptoms in yourself or in people around you , you should consult your family doctor. If necessary, he or she will refer you to a specialist. The following examinations can be used to make a diagnosis :

Medical history

The doctor uses this interview to get a picture of the patient's medical history. Among other things, the doctor will ask the following questions:

• What are the symptoms?
• Do you notice any unsteadiness when speaking or walking?
• How long have the complaints existed?
• Is there any association with animals?
• Have you been out in nature lately?
• Has there been any contact with wild animals?

 
If encephalitis is suspected , the patient should be admitted immediately to the hospital , because every brain inflammation requires immediate treatment, otherwise it can be life-threatening.

Laboratory tests

A laboratory test to reliably detect Borna disease virus in humans and animals can be done at a special institute for tropical medicine, as well as at various university hospitals. There are two ways to detect the pathogen in patients:

PCR test

Using a PCR test, brain tissue or cerebrospinal fluid from people who have already died can be examined for the genetic material of the virus. Even the smallest RNA fragments can be detected and identified.

Antibody detection

For this , the nerve fluid or blood of potentially infected persons is examined for the specific antibodies against the bornaviruses. If the pathogen has entered the organism, the immune system reacts immediately and forms specific antibodies. In living patients, this test, is the only reliable proof of Borna virus.

How is Borna disease virus treated?

There is no approved therapy for the Borna virus as yet. However, special experiments on the cellular level and in animal experiments have shown that treatment with the antiviral agent ribavirin leads to an effect.

What is the prognosis for the Borna virus?

Since there is still no treatment option for this disease, most of those affected unfortunately die within about two to six months after the first symptoms.

How can Borna disease virus be prevented?

The probability of actually contracting Borna disease is very low. Nevertheless, the following measures can help to further minimise the risk :

• Avoid contact with shrews and their droppings.
• Do not keep shrews as pets.
• Never touch dead animals with the bare hand.
• Live shrews found in the house should be lured outside with dog food or cat food.
• Wash hands thoroughly after each animal contact and disinfect afterwards.