Neurological Virus in Horses

By PetMD Editorial on Aug. 8, 2008

Borna Disease in Horses

Borna is a viral disease that occurs in horses (and other warm-blooded animals). First discovered in horses in Germany, it is predominantly a disease found in European and Middle Eastern countries today. It is not known to be currently in the United States.

The Borna disease virus (BDV) causes neurological problems and is fatal in many horses. Horses as well as sheep and other farm animals are natural hosts for this virus, but other animals such as rodents can be affected.

Symptoms and Types

The clinical signs of Borna virus are similar to other equine encephalitic diseases. The incubation time is relatively lengthy and can take upwards of six months from time of infection until clinical signs emerge. This is due to the slow movement of the virus along neurons.

  • Lethargy
  • Poor coordination
  • Blindness
  • Weakness
  • Paralysis
  • Collapse
  • Strange behavior (e.g., head-pressing or found in dark corners)


The mode of viral transmission is still unknown but is thought to be via inhalation or ingestion. Tick transmission is also suspected, as is the spread of the virus via migratory birds.


Definitive diagnosis of Borna virus infection on a live horse is difficult. Samples of cerebral spinal fluid (CSF) only show results typical of many different infectious neurological conditions and cannot distinguish Borna virus specifically. After death, samples of the central nervous system can be sent to laboratories for further examination and identification of the Borna virus made by made at this point.



There is no specific treatment for BDV at this time. However, studies have been conducted to isolate the virus and progress is being made towards better treatment options. If a horse in the U.S. were to be diagnosed with this disease, regulatory authorities should be notified.

Living and Management

In most cases, BDV is fatal in horses but those who do survive have permanent side effects from this debilitating condition, such as reduced brain function or other neurologic impairments that may make ambulation difficult. Euthanasia is often elected.


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