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Japanese Encephalitis Reported in Bali

by Dr Bob Kass - November 11, 2018

The Indonesian Ministry of Health has, this week, alerted the public (including tourists) of a recent outbreak of Japanese Encephalitis in both Bali and Sulawesi (Manado).  Limited details are available, and we await more information to be released by the Indonesian Ministry of Health. In the meantime, news sources (including social media) will seize on this outbreak. It is therefore important for travellers to understand real risk rather than “risk” portrayed by the media.

Much can be done to reduce the risk of contracting Japanese Encephalitis through mosquito avoidance measures, and a vaccine is available.

The Japanese Encephalitis (JE) virus maintained in the environment through an amplifying host such as pigs and birds.  The virus is transmitted by the bite of an infected mosquito that feeds on infected animals, and incidentally bites/ infects humans. The viraemia in humans is not sufficient to support transmission; thus, humans are not responsible for infection to other humans. The incubation period ranges from 4 to 15 days.


The disease is widely distributed in South East Asia. It is generally considered to be a summer month disease (monsoons) when the rice paddy fields are flooded. Outbreaks are commonly observed towards the end of the rainy season but can occur at other times. It is important to remember urban areas can be in close proximity to rice paddy fields and it cannot be assumed to be only a rural disease.

Sero-prevalence studies demonstrate high antibody positivity in children over the age of 15 in some risk areas (Northern Thailand, Laos, China). Acute infectious illness is commonly seen in young children. Adults from these areas are mostly immune.

Travellers are at risk at any age, as they have no natural immunity to the disease. They may get some protection from staying within a population who have natural immunity or are vaccinated (Japan, Korea). Risk assessment must be based on the destination, time of the year and length of stay; however, overall the risk of serious disease is low.

The incidence of Japanese Encephalitis has declined in many countries over the last few years (Taiwan, South Korea, Japan). Much of this decline has been attributed to vaccination, changes in pig farming and a decline in land utilization for rice farming (expanding urbanization).

Risk of exposure can be extrapolated to tourists. After adjusting for the period of risk (5 months of the year) a figure of 1 in 20,000 to 1 in 200,000 per week can be estimated for travellers. This would make the risk quite high for the expatriate worker and those travelling long term in the season of risk. Accumulated risk could also apply to those visiting areas of risk e.g. Indonesia on a regular basis.

Travel-associated JE is rare. A total of 55 cases have been reported in the literature in the period 1973 to 2008 with no evidence that the risk is increasing using 10 year cohorts .  In those well documented (46), 60% cases were in tourists and 16% expatriate workers. The individuals came from 17 different countries and the infection was acquired in Thailand (19), Indonesia (8), China (7), Philippines (5), Japan (4) and Vietnam (3). Median age was 34 years. The disease was fatal in 18% and there were neurological sequelae in 44%. Only 22% survived without problems. These case reports are important as they help to identify those most at risk.

Risk factors include:

  • rural travel
  • living in proximity to farms or jungle areas
  • basic accommodation
  • participation in outdoor activities
  • duration of travel (those with very detailed itineraries 65% had been travelling for more than a month)

The following activities may increase the risk:

  • spending substantial time outdoors in rural or agricultural areas, especially during the late afternoon, early evening and night
  • participating in extensive outdoor activities (such as camping, hiking, trekking, biking, fishing, hunting, or farming)
  • staying in basic accommodation without air conditioning or nets.

Japanese Encephalitis has been reported in Australians visiting resort areas of South East Asia.

Cases have been reported for Australian travellers to Bali. This would be expected given the numbers visiting Indonesia on an annual basis (> 1,250,000). In 2017 a traveller to Thailand, was diagnosed in Melbourne and gave a history of a short-term resort stay in Phuket.  His activities during the stay may have put him at risk but these were unknown.  The case was widely reported and travellers were informed about risk.


Two vaccines, JESPECT and IMOJEV are currently available in Australia (see below for information on the two vaccines currently available). Both vaccines have good protective efficacy but are quite expensive. The previous JE Vax is no longer available.

All travel requires a risk analysis for health issues commonly associated with the type of trip.  Consideration must be taken of the destination, length of stay and season of travel. In the case of Japanese Encephalitis, vaccination is generally recommended for travellers who plan to spend one month or more in endemic areas during the JE virus transmission season. This includes long-term travellers, recurrent travellers (accumulated risk), or expatriates who will be based in urban areas but are likely to visit endemic rural or agricultural areas during a high-risk period of JE virus transmission.

JE vaccination may also be indicated for:

  • travellers to an area with an ongoing JE outbreak
  • travellers to endemic areas who are uncertain of specific destinations, activities, or duration of travel

JE vaccine is generally not recommended for short-term travellers whose visits will be restricted to urban areas or times outside a well-defined JE virus transmission season. However, vaccination may be considered for short-term travel (less than one month) to endemic areas during the transmission season if the traveller plans to travel outside an urban area and undertake certain activities which increase their risk of exposure.


1. MOSQUITO BITE AVOIDANCE (from Globe Medical’s Little Book)

  • Reduce exposure time by modifying activities. The Japanese Encephalitis mosquito is a predominantly night-time biting mosquito (the malaria mosquito is most active between dusk and dawn with peak activity around 9pm; the dengue mosquito is active around dusk (4-6 pm)).
  • Wear light-coloured clothing. Cover arms and legs as much as possible.
  • Tuck trousers into socks and wear covered shoes in areas with ticks.
  • Use permethrin impregnation of clothing, camping gear and curtains.
  • Avoid strongly scented perfumes or toiletries.
  • Sleep in air-conditioned accommodation or under mosquito nets (preferably impregnated with permethrin)
  • Use personal repellents on exposed skin (see table).
  • Use insecticide aerosols, mosquito coils or other agents in the immediate environment


Insect Repellents (IR’s)

Insect repellents date back to ancient times when smoke, plant oils and tars were used. Modern IRs are subject to rigorous testing prior to licensing. This usually involves subjecting volunteers to specifically bred mosquitoes on both treated and control forearms over measured time intervals. Of course, in the real world, repellency may be affected by temperature, sweating and water exposure.

DEET (N,N-diethyl-meta-toluamide) containing insect repellents were developed in the 1950s following military entomological trials.  These chemicals work by vaporizing. The vapor barrier deters the insect by its smell and taste. It is very effective against mosquitoes, ticks and biting flies. The higher the concentration the longer it protects. There seems, however, to be no added benefit beyond 50% concentration. DEET is toxic when ingested and may cause skin irritation in some people. DEET has been used over a long period of time and by many millions of people with few reported serious side effects. In over 50 years there were only 43 case reports (USA) of serious toxicity, most due to overuse or incorrect use.  People may dislike its feel and smell. It is also a plasticizer and can dissolve plastic, synthetic clothing, nail polish and the varnish on musical instruments.


A few precautions should be taken.

  • Apply DEET lightly to exposed areas only
  • Where possible, wash off on returning indoors
  • Do not apply to open cuts or sores
  • Do not use aerosol applications to the face directly. Apply to the hands and then rub on the face avoiding eyes and mouth
  • Do not allow young children (<10 years) to apply it to themselves. Special weaker formulations are available for children. If they have never used it before, it is wise to test a patch on the arm for a few days before applying all over. Do not apply it to their hands that they may subsequently lick. Always stick to the age restrictions stated on the product.
  • If sunscreens are to be used with repellents then the sunscreen should be applied first.  Wait 20 minutes before using the repellent.





6 hrs


5 hrs


3 hrs


2 hrs


Well known DEET containing brands in Australia are Bushmans, Rid, Aerogard Tropical and Repel. See our range of recommended DEET repellents at Globe Medical's TravelShop.



PICARIDIN (KBR3023) or 1 methyl propyl 2-(2hydroxyethyl)-1piperidine carboxylate, is a newer chemical insect repellent. At 20% concentration it is as effective as 20-30% DEET for 4-6 hours. It doesn't feel sticky or damage plastics. Brands available in Australia Repel “New Era” 20% picaridin and “Protect” (19%).

Citronella oil

Citronella oil was discovered in 1901. While it works, it only does so for 20 to 30 minutes.

Products containing extracts form Australian native plants have been shown to provide very little protection, with the exception of oil of lemon eucalyptus (p-methane 3,8- diol or PMD). When trialed, it is equivalent to a weaker DEET, protecting for about 2 hours.

Combination sunscreen/IR products

There is some evidence that the sunscreen may increase DEET absorption, especially if reapplied. The IR may also make the sunscreen less effective.  It is probably best to be specific as to why you are using the chemical on your skin. If you require both, apply the sunscreen first.


Permethrin is similar to a naturally occurring chemical called pyrethrum. Pyrethrum was originally derived from the flowers of the daisy Chrysanthemum. The insecticide properties of the flower have been recognized since the 18th century. The synthesized product has been available for over 30 years. It is colourless, odourless and biodegradable.

Permethrin acts as a “knockdown” insecticide. It is not a personal repellent. It damages the central nervous system of insects that come into contact with it. It is effective against many insects including mosquitoes, fleas, ticks, bedbugs, chiggers, scabies and flies. Permethrin-treated bed-nets have been found to significantly reduce malaria rates in children in Africa and the Western Pacific region.

Once opened to the air, the net should be treated every 6 months to retain its potency. Permethrin can also be used to impregnate clothes, tents and window drapes. It adheres well to fabrics like cotton and will remain effective for between 5 and 10 washes. It is not recommended for skin application.

See our recommended range of permethrin products and insect protection here.




This is a live attenuated viral vaccine produced using gene technology. Two genes from the 17D Yellow Fever vaccine have been replaced by 2 genes from the SA 14-14-2 strain of JE virus. It is given as a single dose and licensed for use from 12 months of age. Seroconversion has been noted as early as 14 days and 99% adults have protective antibody levels by 28 days. Establishment of long term memory has been demonstrated and it is likely to provide good protection for at least 5 years.  Studies to date show protective antibody levels in more than 93% adults at 60 months. There is a similar vaccine in China and evidence from this vaccine suggests long term immunity (> 10 years after a single dose).


This vaccine is manufactured from the SA-14-14-2 strain of JE.  It is an inactivated, cell cultured vaccine, licensed for use in Australia for those 18 years and older. It is a 2 dose schedule (0, 28 days apart). Antibody levels are known to wane over 12-24 months and a booster dose is recommended after 12 months for those with continuing risk provided the original series was less than 2 years previously.  There are no current recommendations for future boosting at this time. The 2 dose schedule should be completed at least 7 days before departure.

An accelerated course can be given at 0,7 days if time is an issue.

Age-related adjustments have been made for the vaccine since first introduced (see below). 

Further details on the vaccine may be sourced at:











Sanofi Pasteur

> 9 months and   < 18 years

0.5ml sc


1-2 years if continuing risk



> 18 years

0.5ml sc








> 17 years

0.5ml IM

0,28 days

> 12 months

> 2 months and < 3 years

.25ml IM


> 12 months

> 3 years and < 18 years

0.5ml IM


> 12 months




Dr Bob Kass

Dr Bob Kass is Medical Director of Globe Medical. He holds specialist qualifications in paediatrics and public health medicine and is one of Australia's pioneers in the discipline of Travel Medicine.