Equine Viral Encephalitis

Description

Viraemia during the acute phase of EEE and WEE. Incubation period of 1-3weeks after experimental infection with EEE or WEE. Incubtion often shorter with EEE. CNS replication within a week

Epidemiology

Transfer via vector: mostly through mosquito salivary transfer Disease amplification occurs during the viraemic phase which lasts until nervous signs develop.

Diagnosis

Clinical signs. Virus isolation can be performed from blood or spinal fluid

Clinical Signs

Worse in unvaccinated animals. Acute signs of EEE and WEE are nonspecific, last up to 5 days and include:

• mild to severe pyrexia
• anorexia
• stiffness

Early signs transient and often missed:

• pyrexia
• mild depression

Disease progression occurs more frequently with EEE than WEE:

• fever may rise and fall sporadically

Cerebral signs often occur a few days post-infection (but can occur at any time. In the acute phase the following may be noted:

• propulsive walking
• depression
• somnolence
• hyperaesthesia
• agression
• excitability
• frenzy in response to sensory stimulation
• conscious proprioceptive deficits

With progression, worsening cerebral cortical and cranial nerve dysfunction may result in:

• head pressing
• propulsive walking
• blindness
• circling
• head tilt
• facial and appendicular muscle fasciculations
• paralysis of pharynx, larynx and tongue
• recumbency for 1-7 days followed by death

VEE may have similar or different clinical presentations to WEE and EEE, which may relate to a persistently hightitre viraemia with VEE and differences in strain pathogenicity:

• pyrexia peaks early and remains high throuhgout the disease course
• mild fever and leukopenia associated experimentally with endemic strains
• severe pyrexia and leukopenia associated with epidemic strains
• diarrhoea, severe depression recumbency and death may precede neurological signs
• neurological signs around 4 days post-infection
• other associated signs: abortion, oral ulceration, pulmonary haemorrhage, epistaxis

• Paralysis of the lips
• Drooping eyelids
• Incoordination

Prognosis

Often fatal, comatose animals rarely survive. Survivors exhibit functional improvement over weeks to months.

Control

Annual vaccination. Vector control. Human vaccination recommended for vets in endemic areas

References

VEE in Donkeys