see also:

• WHO fact sheet
• malaria
• dengue fever
• viruses
• Murray Valley encephalitis (MVE)
• https://www.health.vic.gov.au/infectious-diseases/japanese-encephalitis-virus

• mosquito-born flaviviral infection present in most parts of Asia extending south to the tip of Australia (Outer Torres Strait Islands)
  • HOWEVER was detected for the 1st time in Australia in Feb 2022 in Echuca, southern and western NSW and in Qld associated with piggeries - 21 piggeries across 4 states have been infected
  • in March 2022, a Victorian man in his 60s from the north parts of Vic becomes 1st death to JEV in Victoria, while a NSW man in his 70's became NSW's 1st death while it is thought a death in SA was due to JEV
• travelers have low risk if visiting urban areas
• risk is higher if in rural or periurban areas, especially in warmer months although occurs all year round in tropical and subtropical regions
• major outbreaks of JE occur every 2-15 years
• mosquitoes do not get the virus from infected humans as viraemia is not high enough, but get it from infected pigs, horses or water birds and thus human infections are usually acquired in non-urban areas
• infection with JE virus confers lifelong immunity

• Culex species of mosquitoes
  • in SE Asia rice fields, this is particularly Culex tritaeniorhynchus
  • other species in Australia of uncertain significance for JEV may include Cx. gelidus, Ae. kochi, Ochlerotatus notoscriptus (probably not a vector for JEV)¹⁾, and Verrallina funerea
  • in Torres Strait, it is the Culex annulirostris (the common banded mosquito), which may be the vector in inland Australia but this is yet to be proven
    • this mosquito also can carry Ross River virus (RRV), Barmah Forest virus (BFV), Murray Valley encephalitis (MVE)
    • breeds in fresh water and is most active at dusk and dawn
    • these can also transmit JEV to mice, horses and flying foxes ²⁾

Culex annulirostris image courtesy https://wrbu.si.edu/vectorspecies/mosquitoes/annulirostris

• water birds such as herons and egrets
• pigs are important amplifier hosts
• NB. humans, horses and other large vertebrates are dead-end hosts in the JEV transmission cycle producing not a high enough viremia to be infectious for mosquitoes

• 1st recognised as a disease in Japan in 1871
• virus first isolated in Japan in 1935
• it is endemic mainly in SE Asia and Southern Asia as far south as the tip of Australia
• introduced into the Torres Strait islands in 1995, Papua New Guinea human cases in 1997, and onto the mainland of northern Australia (Cape York) in 1998
• in 2022, cases were found in inland Australia for the 1st time, particularly along the Murray River in association with piggeries

• usually 5 to 15 days

• 99% are asymptomatic or have only mild symptoms
• in children, gastrointestinal pain and vomiting may be the dominant initial symptoms
• in endemic regions, most cases are children with no past exposure and 1 in 250 develop severe encephalitis illness:
  • rapid onset of high fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis and ultimately death in 30%
  • of those who survive, 20%–30% suffer permanent intellectual, behavioural or neurological problems such as paralysis, recurrent seizures or the inability to speak
  • children aged under five and older people who are infected with JE are at a higher risk of developing more severe illness

• general mosquito precautions such as insect repellents and long sleeved clothes if visiting at risk zones
• consider vaccination if either:
  • planning extended time in endemic zones
  • work around or with pigs in Australia

• testing for JEV-specific IgM antibody in CSF (preferred as has lower false positive rates from prior infection or vaccination than in serum) or serum, using an IgM-capture ELISA
• PCR testing of blood or CSF

• supportive care