Borna Disease in Horses: Neurological Signs and Veterinary Investigation
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By Dr Duncan Houston
A horse that suddenly behaves differently, stumbles or appears unable to see needs a veterinarian urgently. Borna disease is one possible explanation in particular European regions, but its name should not distract from the many other conditions that can produce similar signs.
Understanding where this disease occurs and how it is investigated helps owners give useful information without jumping to a diagnosis. It also avoids unnecessary assumptions about an affected horse spreading the infection through a yard.
Quick Answer
Classical Borna disease can cause severe, often fatal inflammation of the brain and spinal cord in horses. Contact your vet immediately for new neurological signs, stop riding and avoid moving the horse until advised. Diagnosis requires specialist interpretation; a negative blood test does not reliably exclude the disease.
What current evidence says about transmission
Borna disease virus 1, or BoDV-1, is associated with parts of eastern and southern Germany, Austria, Switzerland and Liechtenstein. The known natural reservoir is the bicoloured white-toothed shrew. Infected shrews can release virus into their surroundings.
According to the Friedrich-Loeffler-Institut’s bornavirus guidance, horses are incidental, dead-end hosts. They do not shed infectious virus, and natural transmission from an infected horse to another mammal has not been documented. People can also acquire BoDV-1 infection from the reservoir, so this distinction should not be turned into a claim that the virus poses no human health concern.
Signs and immediate priorities
Possible signs include altered behaviour, circling, incoordination, unusual chewing movements and apparent blindness. These signs do not confirm Borna disease. The horse’s location, travel history and clinical examination all affect which explanations are plausible.
| What you notice | Immediate priority |
|---|---|
| New stumbling, head tremors or unusual behaviour | Stop ridden or driven work and call your veterinarian promptly. |
| Circling, blindness, repeated falls or seizures | Request emergency assistance and keep people out of the horse’s path. |
| Several horses with fever or neurological signs | Report the group pattern immediately and stop horse movements pending advice. |
| Concern based only on reading about Borna disease | Discuss the actual signs and geographic history rather than requesting an isolated screening test. |
Emergency steps for owners
- Call your vet and describe exactly what changed, when it began and whether the horse has travelled.
- Keep the horse in the safest accessible quiet area. Do not attempt risky relocation, forced walking or balance tests.
- Keep children, visitors and unnecessary handlers away. A frightened or poorly coordinated horse can injure someone unintentionally.
- Avoid contact with saliva and use the precautions your vet recommends while infectious causes are assessed.
- Pause transport, shared equipment and contact with other horses until the vet gives a plan. Record a short video only from a safe position.
These initial precautions address an undiagnosed neurological illness. They are not evidence that horses transmit BoDV-1 to one another. Call a receiving hospital before transport so staff can plan safe handling and appropriate infection precautions.
How the diagnosis is investigated
The veterinarian first assesses the nervous system and considers urgent alternatives. Blood tests, imaging, spinal fluid examination or other tests may be recommended according to the findings and handling risk.
The FLI reference laboratory’s diagnostic guidance explains that testing living incidental hosts is difficult because the virus is concentrated in nervous tissue. Antibody results can support suspicion but may be falsely positive. Virus detection in appropriate tissue provides stronger confirmation, and definitive investigation may require samples collected after death. A routine blood PCR or a single negative spinal fluid result should not be treated as a simple clearance test.
Other explanations must stay on the list
Trauma, toxic exposures, metabolic problems and other infections can affect coordination or behaviour. Depending on location and history, the vet may consider equine herpesvirus, West Nile virus, rabies or other regional diseases. The Merck guide to equine nervous system disorders describes why the pattern of abnormalities helps localise the problem but does not identify its cause by itself.
Care decisions and common mistakes
Borna disease carries a serious prognosis. Supportive care, safe nursing and welfare decisions need specialist veterinary guidance; owners should not rely on an advertised supplement or antiviral protocol as an established cure.
- Do not ride a horse to see whether it “works out” of incoordination.
- Do not assume every neurological horse in Europe has Borna disease.
- Do not use one negative screening result to end an investigation.
- Do not handle sick or dead wildlife while trying to identify a source.
Frequently asked questions
Can I catch Borna disease directly from my horse?
Natural transmission from infected horses has not been documented. Follow veterinary advice because an undiagnosed neurological illness may have another cause.
Will reducing wildlife access guarantee protection?
No. Protecting feed stores and seeking local advice about wildlife contamination are sensible, but no yard measure guarantees prevention.
Is a positive antibody result definitive?
No. A specialist laboratory must interpret it alongside the clinical picture and additional evidence.
For owners, the practical priority is a safe, prompt investigation of neurological change. Clear observations and an accurate travel history are more useful than trying to identify this rare disease at home.
For help understanding your animal’s care and preparing questions for your veterinarian, visit ASK A VET™.
