Investigating Japanese encephalitis in animals

Clinical presentation

Many cases of Japanese encephalitis (JE) infection in animals are sub-clinical. Signs of disease are most commonly seen in pigs and horses. Testing of animals showing clinical signs consistent with JE disease are conducted by Biosecurity Queensland as disease investigations at no charge, however wider diagnostic testing will not be undertaken.

The clinical presentations below should be observed to meet a disease investigation.

Clinical presentation in pigs

  1. Reproductive disease in sows are characterised by abortion, stillbirths or mummified foetuses, paretic or clinically affected piglets that die soon after birth, above the expected level for the enterprise.
  2. Shaking/trembling, ataxic or convulsing piglets (up to 6 months) that do poorly with variable pyrexia.
  3. Orchitis, decreased sperm number or motility in semen, or abnormal spermatozoa.

Clinical presentation in horses

  1. Neurologic disease characterised by ataxia (including stumbling, staggering, wobbly gait, or incoordination).
  2. Neurologic disease without ataxia, characterised by 2 or more of the following:
    • facial paralysis
    • muscle tremors/fasciculation
    • hyperaesthesia
    • circling
    • blindness
    • recumbency or inability to stand
    • hind limb weakness
    • multiple limb paralysis
    • altered mental state
    • hypermetria
    • depression.

Note: Fever is an inconsistent finding, usually as a result of the late onset of central nervous system (CNS) signs relative to the time of infection and is not an essential component of the clinical description. Behavioural changes including somnolence, listlessness, apprehension, or periods of hyperexcitability may occur. Other common clinical signs include colic, lameness and anorexia.

Horses – important note

Because of the clinical similarity to Hendra virus infection it is important to take appropriate precautions when assessing, sampling, and treating affected horses.

For more information, read Hendra virus sampling, submission and testing.