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.

The epidemiology of Japanese encephalitis (JE) is complex and involves a cycle of virus transmission between waterbirds, infected mosquitoes and susceptible amplifying animal hosts (pigs).

While all piggeries that are exposed to infected mosquitoes are at risk of continuing that cycle and spreading disease, piggeries with confirmed or suspected infection have a higher level of risk and need to implement risk mitigation strategies.

Learn more about controlling mosquitoes in piggeries.

JE is a public health risk. To minimise the risk of infection, all people who work with potentially infected pigs, work in areas in which infected vectors may be present, or handle Japanese encephalitis virus (JEV) infected material should take appropriate precautions.

You can protect yourself from vectors by:

• wearing a loose-fitting, long-sleeved shirt with long pants, and covered shoes
• using repellents that contain diethyltoluamide (DEET) or picaridin
• applying insect repellent to all exposed skin during your workday. Ensure you read the repellent label for reapplication times and re-apply accordingly. A range of repellents and insect sprays are available.

Although human infection is primarily via the bite of a mosquito, any potentially JE-infected material must be handled appropriately. Humans may be infected by exposure to infectious material (e.g. via needlestick injuries, aerosols or broken skin or mucous membranes). When examining animals, collecting and handling samples, personnel should wear appropriate personal protective equipment (PPE) which may include:

• gloves (double-layered)
• disposable coveralls
• boots
• water-resistant dressings covering cuts and abrasions
• safety eyewear or face shield
• respirator or face mask (minimum P2).

Hands, face and arms should be washed immediately after sample collection with an effective disinfectant and use disposable PPE.

At risk employees should consider protection against JE with a vaccination. Consult your health practitioner or read more about JE vaccination.

Although horses are considered 'dead end' hosts and do not play a role in transmitting JEV, the above precautions should be followed to control possible human exposure to Hendra virus or other zoonotic infections in horses.

Where to submit samples

Submit samples from clinically consistent cases directly to the Biosecurity Sciences Laboratory (BSL), using this advice sheet:

• specimen advice sheet

Laboratory testing of pigs and horses with signs consistent with clinical Japanese encephalitis (JE), where appropriate samples have been submitted, will be fully subsidised by the Queensland Government.

Samples required

Complete and suitable samples support a thorough diagnostic work-up and improves the likelihood of reliable and meaningful results.

Post-mortem

Post-mortem specimens should be collected from animals with neurological signs killed in the acute stage of the disease or from recently dead animals.

Pigs less than 6 months or aborted foetuses

• Fresh specimens (collected into separate, clearly labelled containers)
  • placenta (from aborted foetuses)*
  • brain (aseptically removed if possible)*
  • spinal cord*
  • cerebrospinal fluid (CSF)
  • tonsil*
  • lung*
  • heart*
  • spleen*
  • liver*
  • kidney*
  • abdominal and/or thoracic fluid
• Formalin-fixed specimens (*as listed above) in 1 container per animal necropsied
• Whole fresh aborted or stillborn foetuses are also suitable for submission where samples can't be collected on the farm

Horses with neurological signs

• Appropriate specimens for Hendra virus exclusion—Hendra virus should be excluded before progressing to invasive sampling or post mortem
• CSF (in sterile container)
• Fresh and formalin-fixed tissues (including brain and spinal cord)

Ante-mortem

• From animals in the acute stage of disease, collect whole blood (EDTA) and serum samples for virus detection and serology. For serum, collect at least 7–10mL of blood from animals in the acute phase and convalescent stage of disease (2–4 weeks apart).
• CSF should be collected from animals presenting with neurological signs. Hendra virus should be excluded first for horses.

Ideally, separate serum from clot before shipment and submit both.

Fresh semen from boars with sperm abnormalities may be considered as an additional sample for virus detection in pigs.

Transporting samples

• Chill blood samples and unpreserved tissue samples at 4°C. Note: Do not freeze samples
• Send samples in esky with frozen gel packs
• Formalin-fixed tissue can be sent at room temperature
• If mummified, stillborn or abnormal piglets are submitted they should be sent:
  • double bagged—using strong plastic to avoid leakage of sample
  • chilled—on ice or with ample frozen gel packs
• Ensure the necessary paperwork is submitted in hardcopy with the specimens (place in a separate zip-lock bag).

Contact BSL if you have any queries about submitting your samples.

Laboratory testing

A confirmed diagnosis of JEV infection can be made through these methods:

• isolation and identification of JEV
• detection of JEV by nucleic acid testing
• seroconversion or a significant increase in JEV-specific* antibody level by testing paired serum samples in a virus neutralisation test
• detection of elevated levels of JEV–specific* IgM antibody in CSF.

Evidence of exposure to JEV can be based on:

• detection of elevated levels of JEV-specific* IgG antibody in CSF
• detection of elevated levels of JEV–specific* antibody (IgM or IgG) in serum.

Veterinarians may be asked by pig producers or horse owners for advice around mitigating the risk of infection or preventing disease spread which may include:

• undertaking mosquito control/management practices in and around piggeries
• managing contact of horses with mosquitoes.

In Queensland, Japanese encephalitis should be considered a potential risk when mosquitoes are present and therefore mosquito management should be included as part of biosecurity planning.

Veterinarians can also discuss risk mitigation measures with a Biosecurity Queensland veterinary officer by phoning the Customer Service Centre on 13 25 23.

More information

• Read more about Japanese encephalitis on this Business Queensland website.
• Learn more about Japanese encephalitis from Queensland Health.