Page 1087 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1062 CHAPTER 10

VetBooks.ir 10.20 10.21

Fig. 10.21
A horse infected
Fig. 10.20 Dysphagia and dementia associated with with EEE which
EEE. (Photo courtesy FT Bain) presented with
severe ataxia and
recumbency and
and compulsive walking or chewing. WEE does required the use of
not usually progress beyond non-specific initial a sling. The horse
signs or, less commonly, mild CNS signs such as eventually died.
those above. EEE typically progresses to severe
CNS deficits that occur secondary to diffuse cere-
brocortical disease. Signs associated with more Serological testing is helpful, with a four-fold rise
severe disease in EEE include apparent blindness in antibody titres being diagnostic. However, a
and circling, excitement and aggressive behaviour, four-fold rise may not be detected because antibody
laryngeal, pharyngeal and tongue paralysis, dys- levels rise rapidly after infection and a delay in tak-
phagia (Fig. 10.20) and signs of brainstem dys- ing the acute sample frequently results in sampling
function such as head tilt, nystagmus, strabismus during the peak antibody titre. Another problem
and pupil dilation (Fig. 10.21). VEE may also frequently encountered with serological testing is
cause inapparent infections, signs similar to those that horses with EEE often do not live long enough
of other encephalitis viruses, or produce signs such for comparison of paired samples. High immuno-
as epistaxis, pulmonary haemorrhage, oral ulcers globulin M (IgM) titres suggest recent exposure to
and diarrhoea that may be unrelated to CNS dam- EEE virus and may be detected via enzyme-linked
age. Seizures can occur with any of the alphavirus immunosorbent assay (ELISA). Definitive ante-
infections and sudden death may also occur despite mortem diagnosis can also be made on the basis
seemingly insignificant clinical signs. of viral isolation or identification of viral nucleic
acid by reverse transcription (RT-)PCR. RT-PCR
Differential diagnosis is a sensitive and specific test for detection of viral
Other viral causes of encephalitis should be consid- nucleic acid in CNS tissue or CSF. EEE, WEE
ered depending on the geographical incidence of or VEE viruses can be isolated from brain tissue
individual diseases and time of year. of infected horses via Vero-cell culture or mouse
inoculation. Immunohistochemistry testing can
Diagnosis also be performed on brain tissue. Virus isolation
Establishing a definitive diagnosis is important from serum is usually unsuccessful. Other findings
to allow implementation of control measures, that are not specific for alphaviruses are peripheral
but it can be challenging. Clinical signs are non- leucocytosis and increased cellularity and elevated
specific or similar to those of other encephalitides. protein concentration of CSF.