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Japanese Encephalitis Virus

Published on Monday, 14 March 2022 at 1:15:06 PM

Japanese encephalitis virus (JEV) is an acute mosquito-borne arbovirus disease associated with abortion in pigs, and inflammation of the brain in humans and horses. It is spread through mosquito bites and is more common in areas of increased mosquito activity.

Western Australian pig producers and horse owners are urged to monitor for signs of Japanese encephalitis, after the disease was confirmed in at least 22 commercial pig farms across eastern Australia, including New South Wales, Victoria, Queensland, and South Australia. There is currently no evidence of JEV in Western Australia (WA), however, an increase in surveillance in mosquitoes, sentinel chicken flocks, pigs and horses are being undertaken to monitor the situation.

Transmission: JEV is transmitted to humans through bites from particular types of infected mosquitoes. The virus exists in a transmission cycle between mosquitoes, pigs and/or water birds. Pigs are an important host with the virus potentially occurring at high levels in their blood for 4-6 days. Mosquitoes that feed on infected pigs during this period can become infected with the virus and then transmit it to humans. After a person is bitten by an infected mosquito, it takes approximately five to 15 days for the first symptoms to appear.

JEV cannot be transmitted from human to human or by eating meat from an infected animal.

Signs and Symptoms: Approximately 99% of people infected with JEV have no symptoms. Those that develop symptoms may experience a fever and headache. Severe disease is characterised by an acute encephalitis (inflammation of the brain), with sudden onset of high fever and chills, severe headache, photophobia, neck stiffness, nausea/vomiting, convulsions, and coma. Of these severe cases, approximately one-third die, and one-third are left with permanent disabilities.

Treatment: There is no specific treatment. Treatment usually involves management of the symptoms.

Spread: You can help stop the virus spreading by avoiding being bitten by mosquitos.

Mosquito management advice

  • Ensure effluent ponds or water bodies have sufficient capacity to contain all excess wastewater from pig production and are well maintained to prevent mosquito breeding
  • Ensure misting/irrigation systems do not create standing water in or around pig sheds
  • Level or drain depressions in the ground that may hold water
  • Empty, cover or discard any water holding containers, including rubbish/debris, to reduce mosquito breeding on the property
  • Screen water tanks with insect‑proof mesh, including inlet, overflow, and inspection ports.
  • Ensure guttering is not blocked and does not hold water
  • Apply residual barrier sprays to buildings, structures, and vegetation (ensure any application of pesticides is in accordance with the registered product label and will not compromise livestock production standards or withholding periods)

Advice for horse owners seeking information about ways to reduce the risk of exposure to biting mosquitoes for their animals:

Horse owners can also put measures in place to help their horses avoid mosquito bites.

  • During hotter months put a light cotton rug on them, a fly mask, and if the horse allows, apply a safe insect repellent. Do not spray the repellent around or above their eyes
  • The Australian mosquito that transmits JEV feeds at night and is reluctant to enter dwellings, so stabling horses between dusk and   dawn is a valuable action
  • Rugging and hooding with lightweight permethrin fabric may help protect horses not stabled overnight

What to do if you suspect JEV in your animals

JEV is a reportable disease. If you suspect JEV in any animal immediately contact your local DPIRD Veterinary Officer or phone the all-hours Emergency Animal Disease Watch Hotline (1800 675 888).

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