Page 1085 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1060 CHAPTER 10

VetBooks.ir 10.19 INFECTIOUS NEUROLOGICAL
DISEASES

BORNA DISEASE (NEAR
EASTERN ENCEPHALITIS)

Definition/overview
Borna disease is a sporadically occurring encepha-
litic disease caused by Borna disease virus reported
in horses, humans, sheep, goats, cattle and rab-
bits. Outbreaks have been reported in countries in
Central Europe and the Middle East.

Aetiology/pathophysiology
Naturally occurring Borna virus infections and
Fig. 10.19 Occipitoatlantoaxial malformation in an their resulting diseases mainly affect horses and
Arabian foal. Note the exaggerated dorsal flexion of the sheep in Central Europe. Borna virus, an RNA
proximal cervical vertebrae. (Photo courtesy FT Bain) virus of the Flaviviridae family, causes a severe,
usually fatal encephalitis. The reservoir host in
Europe is thought to be the shrew (Crocidura leu-
the abnormal head and neck posture, whereby they codon), which sheds high viral loads in body fluids
are held in extension and appear stiff when the horse (saliva, urine, tears, skin and faeces). The incuba-
moves. tion period can be from weeks to several months
after exposure.
Differential diagnosis
AO luxation; cervical trauma. Clinical presentation
Initial clinical signs are rather non-specific, includ-
Diagnosis ing dullness, depression, anorexia and pyrexia.
In horses with neurological deficits, the neurological Neurological signs follow, and are consistent with
examination will localise the lesion to the cervical an encephalitis, such as head pressing, ataxia,
spine. On palpation of the neck, some abnormali- circling, repetitive chewing and tooth-grinding.
ties of the atlas and axis may be detected, including Eventually, horses become paretic, develop blind-
lack of movement of the AO joint and small stubby ness and coma and finally die, in at least 80% of
wings (rather than large broad wings) of the atlas. cases.
Characteristic clinical signs and observation or pal-
pation of the malformation is highly suggestive of Differential diagnosis
OAAM, but radiography/CT is required for confir- A variety of other viral causes of encephalitis should
mation (see Fig. 1.445). The bony lesions are appar- be considered, depending on the geographical area.
ent on radiographic images and a myelogram will
illustrate the site of spinal cord compression. Diagnosis
Clinical findings are not specific for Borna disease.
Management Ante-mortem diagnosis is based on the identification
Laminectomy has been used to alleviate spinal of antibodies in the serum and CSF. Gross pathol-
cord compression and clinical signs. It has been ogy is usually unremarkable. Histologically, there is
suggested that surgical fusion of the atlantoaxial evidence of a non-purulent meningoencephalitis and
joints, with or without laminectomy, could be used inflammatory foci in the grey matter that consist of
as a treatment. lymphocytic perivascular infiltrates.