Borna Disease

Borna disease is a sporadic, transmissible, progressive neurologic disease of horses, cats, cattle, and

sheep. Natural infections have been reported in

other equine, rabbits, and ostriches. Borna disease

virus (BDV) has been experimentally transmitted to a

very wide range of species, from chickens to 

nonhuman primates. Evidence in recent years 

indicates that BDV also infects humans, where it may

be associated with various neuropsychiatric 

disorders, including schizophrenia.

Clinical Signs

Borna disease is a subacute, viral

encephalomyelitis, which is a type of brain infection.

Historically, the disease has been reported in horses,

and occasionally in sheep, in endemic areas in

Germany and Switzerland. Through blood testing,

evidence of infection has been found in clinically 

normal horses and other animal species in Israel,

Luxembourg, the Netherlands, Poland, Russia,

Sweden, the United Kingdom, and the United States.

In cases of natural infection in horses and sheep,

the incubation period is usually 2–3 months. This

may be reduced to 4–8 weeks in experimentally

infected animals challenged by intracerebral 

inoculation. The characteristic clinical signs of Borna

disease are the result of disturbances in motor and

sensory functions and changes in behavior. Initially,

affected animals may display incoordination (ataxia),

yawning, chewing movements, hypersensitivity to

stimuli (hyperesthesia), loss of appetite, mild colic,

and muscle contractions. The severity of signs

progress to severe depression, sawhorse stance, and

leaning against objects. Terminal cases exhibit rapid,

involuntary eye movement (nystagmus). The duration

of clinical illness is normally 1–3 weeks. The casefatality rate ranges between 60 and 95 percent for

horses and greater than 50 percent for sheep.

Animals that survive may remain neurologically

impaired permanently.

Causal Agent 

The cause of Borna disease is an enveloped,

negative-strand RNA virus that has yet to be fully

characterized. It only affects the nervous system and

is only disseminated from the site of infection through

the nerves (intra-axonal transport). BDV appears in

the brain and cerebral spinal fluid in 3 days in 

animals infected by the intracerebral or intranasal

route. Less commonly, the virus can be isolated from

salivary and mammary glands and the nasal mucous

membrane. The virus can be grown in cell culture, in

which it produces no detectable cellular changes.

Origination and Development

Based on detailed laboratory examination of

nervous tissue from horses affected with Borna 

disease, evidence suggests that BDV enters the 

central nervous system (CNS) through nerve endings

in the nose and throat area.

The CNS of an animal affected with Borna 

disease does not develop changes visible to the

naked eye. Microscopically, the disease is characterized by an inflammation of nerve cells in the brain.

Lesions result from an immune system response to

the virus, which can be demonstrated using 

immunocompromised animals. Rats that are 

newborn, experimentally immunocompromised, or

have had the thymus removed do not develop clinical

signs of the disease despite productive BDV 

replication in the CNS. Such animals do not 

experience any interference with their vital functions

since the disease itself is the result of a virus-induced

cell-mediated response by the host.

Epidemiology

It is currently believed that transmission of BDV in

cases of natural infection occurs through direct 

contact with infective nasal secretions and saliva or

via contaminated food and water.

The results of recent studies suggest that many

cases of BDV infection are clinically inapparent and

that the virus is more widespread throughout the

world than previously recognized. It is now known

that BDV no longer exists only in the traditional

endemic regions of Switzerland and Bavaria,

Germany. Borna disease should be included in any

differential diagnosis for equine neurologic disease.

The actual significance of BDV in the cause of 

schizophrenia and other neuropsychiatric disorders in

humans has yet to be determined. Additional studies

are required to establish whether Borna disease in

horses and other species of animals occurs more

commonly than has been reported up to this point.

Factsheet

 

 
 

APHIS
Additional Information

For more information about Borna disease, 

contact:

USDA, APHIS, Veterinary Services

4700 River Road, Unit 41

Riverdale, MD 20737–1231

Phone: (301) 734–8073

Fax: (301) 734–7817

or visit the APHIS Web site at

www.aphis.usda.gov/vs/.

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United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture