32 CLINICAL FOCUS
32 CLINICAL FOCUS
15 SEPTEMBER 2023 ausdoc . com . au
Therapy Update
Japanese encephalitis
Travel medicine
Professor Nick Zwar is a GP and executive dean at the faculty of health sciences and medicine , Bond University , Queensland and is chair of the RACGP travel medicine specific interest group .
Vaccination is now recommended for travellers spending one month or more in endemic areas in Asia and Papua New Guinea during the transmission season .
NEED TO KNOW
Vaccination recommendations for Japanese encephalitis have been updated , in line with changes in disease epidemiology resulting from climate and environmental changes .
While still relatively uncommon , Japanese encephalitis is potentially very serious , with mortality as high as 70 % in those with symptomatic infection .
It is prudent to advise travellers to affected areas about preventive strategies , including protection from mosquitoes as well as vaccination when indicated .
Online tools can aid decision-making about who to vaccinate as well as discussions about risk versus benefit of vaccination .
JAPANESE encephalitis has been in the news since early 2021 when cases of the disease , previously only seen in returned travellers or in people living in the Torres Strait , started appearing in other parts of Australia including the southern states . 1
Since January 2021 there have been 45 human cases notified of which 36 were confirmed with definitive laboratory evidence . These cases resulted in seven deaths , two in NSW , two in SA , and one each in Victoria , Queensland and the NT . Prior to 2021 local transmission was only seen infrequently in the Torres Strait and Cape York with three cases on Badu Island in 1995 and one on Badu Island and the Cape York Peninsula respectively in 1998 . 1
Japanese encephalitis ( JE ) in returned travellers has been uncommon , with 12 cases reported to the National Notifiable Diseases Surveillance System in the period 2001 to 2016 . The most recent fatality in a returned traveller was in November 2019 in a 59-year-old man who had spent extended periods of time in Bali .
Travel vaccination recommendations updated
In 2022 the Australian Immunisation handbook recommendation for JE vaccination and travel was updated and expanded . 2 JE vaccination is now
There are two Japanese encephalitis vaccines currently available in Australia . recommended in travellers spending one month or more in endemic areas in Asia and Papua New Guinea during JE transmission season . This includes people who will be based in urban areas but are likely to visit endemic rural or agricultural areas . The handbook also recommends considering vaccination for shorter-term travellers , particularly if : the travel is during the wet season ; there may be ongoing travel to at-risk areas ; there is considerable outdoor activity during the travel ; or the traveller is staying in accommodation without air-conditioning , screens or bed nets .
Areas of risk
The major areas of JE risk are the Indian subcontinent , South-East Asia and China . JE is also thought to be widespread in Papua New Guinea . Disease transmission occurs year-round in tropical areas and during the rainy season ( April to October ) in the temperate and northern tropical areas of countries such as China , India , Vietnam , Cambodia and Myanmar . Although , as stated previously , the risk is higher with longer-term travel , cases have occurred in short-term travellers to holiday destinations , such as Bali , which are close to areas of intense transmission .
Evolving epidemiology
The changes to the Australian Immunisation Handbook reflect the changing epidemiology of JE . In some countries in Asia , JE risk has declined ( Japan , Taiwan , South Korea ) or been eradicated ( Singapore ), related to changes in the pig industry , less land used for rice farming and improved socioeconomic circumstances . However , in other Asian countries , such as India , Nepal and Vietnam , there is evidence that the risk is increas-
Vaccination should be considered for shorterterm travellers , particularly if the travel is during the wet season .
ing . 3 This is thought to be related to the effects of climate change , population growth and struggling vaccination programs . Climate change has seen culex mosquitoes that transmit JE found at higher latitudes and at higher altitudes than previously . The increase of flooding events associated with climate change provides more breeding sites for mosquitoes and the increased proximity of human populations to rice paddies and piggeries is another factor in facilitating transmission .
Pathophysiology
JE is caused by a flavivirus and is in the same family as viruses that cause Murray Valley encephalitis , dengue , Kunjin and Zika . It is transmitted from wading birds to domestic animals , usually pigs ( an important amplifying host ), and then occasionally to humans by mosquito vectors , including culex mosquitoes that bite in the evenings . The risk of infection is greatest in rural areas near rice paddies and animals . Most human infections are asymptomatic with < 1 % of those infected developing symptoms , however the rate is likely to be higher in non-endemic populations . 1 It has been estimated that the incidence of symptomatic disease could be as high as one in 25 in non-immune returned adult travellers . 4 JE can cause a non-specific febrile illness with symptoms of fever , headache , nausea and vomiting . Only a small proportion of those infected with the virus ( about one in 200 ) develop encephalitis causing convulsions , delirium and paralysis . The mortality rate of JE can be as high as 70 %, especially in those with cerebral involvement , although with high-quality medical care the death rate is more often about 10 %. Among survivors , neurological sequelae are common . Infection in pregnancy is associated with a high risk of intrauterine infection and fetal death .