Japanese encephalitis – ‘rare’ doesn’t mean ‘never’ Heading to Asia? Japanese encephalitis is one of the many mosquito-borne diseases you might hear mentioned as you prepare for your trip. Potentially, it's more lethal than dengue and Chikungunya, the better known, but (generally) more benign diseases spread by mozzies in tropical and sub-tropical regions.
In fact, in terms of potential severity, Japanese encephalitis (or JE as it is known) ranks closer to yellow fever or malaria, but with far fewer cases – particularly among travellers.
There have been only 62 documented travel-related cases of JE in the past 40 years, although an estimated 30,000-50,000 people living in the rural rice-growing, pig-farming areas where the disease typically occurs are infected each year.
That makes JE a rare event among travellers. But, 'rare' does not mean 'never', as 2 recent worrying cases involving travellers show.
Two unusual recent cases
They're worrying because their separate itineraries did not fit the usual criteria for recommending JE vaccination.
Both patients were healthy young men who spent only a short time in Thailand and had no exposure (as far as we know) in the higher-risk rice-growing areas.
CASE 1 – A 20-year-old Spaniard who travelled to Thailand for a martial arts competition in March this year enjoyed a very common itinerary in popular areas of Thailand. It began with 2 days in a Bangkok hotel, followed by stays in bungalows on two beaches (Chaweng and Lamai) on Koh Samui Island. He visited rural areas, including a forest and waterfalls, where he recalls receiving mosquito bites. Four months later, including a 2-month stay in hospital, the previously healthy young sportsman is able to walk again, if unsteadily, but has memory loss. His case was described in a Eurosurveillance report.
CASE 2 – A Chinese man, also aged 20, became ill with a fever in Thailand in late August after a 3-week stay. Fortunately, was able to return home and is in a stable condition undergoing treatment in hospital in Hong Kong. It is not yet known where he stayed or the places he visited while in Thailand. (Hong Kong has now seen 2 'imported' and 4 locally acquired cases in the past two years.) Source: The Centre for Health Protection (CHP) of the Department of Health (DH) – Hong Kong.
Which travellers are most at risk?
Travellers considered to be most at risk of JE in Asia are those who are:
- staying longer than month, especially in rural areas during the local JE transmission season.
- Working or studying in ANY areas of a country where JE is common (endemic) for an extended period.
- visiting an area with an ongoing JE outbreak.
- uncertain of specific destinations, activities, or duration of travel in an endemic area.
Typically, JE vaccination is recommended for backpackers passing through regional areas, rural-based aid workers, and expats living or working in an endemic region.
However, because travellers have been infected after shorter periods of travel, the Australian Immunisation Handbook recommends that doctors consider advising vaccination if:
– Travel is taking place during the wet season, and/or there is considerable outdoor activity, and/or the accommodation may not be mosquito-proof.
– The traveller is spending a year or more in Asia (except Singapore) – even if much of their time will be spent in urban areas, and
– The itinerary includes a month or more in Papua New Guinea, particularly during the wet season.
Rare risk of severe illness
These young men were doubly unlucky: Firstly, to get JE and, secondly, to develop a severe illness.
For most of those infected, there are no symptoms or they're mild and self-limiting.
But, for the less than 1% whose infection is severe, the statistics tell us that 20-30% will die and 30% - 50% will suffer a severe disability.
In short, JE is a travel disease with a relatively low risk, but with potentially severe consequences.
There are two excellent vaccines against Japanese encephalitis that should be considered by all travellers visiting Thailand and other risk areas of Asia, especially those expecting to get off the beaten track.
Discuss your plans and detailed itinerary with your doctor, ideally one experienced in travel medicine.
- Dr Eddy Bajrovic, Medical Director, Travelvax Australia.
More about Japanese encephalitis
About the virus – Japanese encephalitis (JE) is an arthropod-borne virus (arbovirus) closely related to the West Nile, St Louis encephalitis, yellow fever, and dengue fever viruses.
The symptoms – The virus affects the brain. Most JE virus infections are mild (fever and headache) or without apparent symptoms. However, less than 1% of infections results in severe disease that starts with high fever and may progress to coma and death.
How it's spread – JE is transmitted in an 'enzootic cycle'. That is, mosquitoes usually transmit the disease to people after biting infected animals - mainly pigs and wading birds - that serve as 'hosts' to the virus. There is no person-to-person transmission.
Where it occurs – JE occurs across most of Asia and parts of the western Pacific, where an estimated 35,000- 50,000 cases occur each year. Most are among local people living in rice-producing areas of 3 main regions: China (June through October) and Korea (May-October); Indian subcontinent – India (May–October, especially northern states; year-round in some southern states), Bangladesh (May–October), Nepal (June-October), Sri Lanka (year-round; variable monsoon peaks), and Pakistan (unknown); Southeast Asia – Myanmar (May–October), Thailand (year-round; seasonal peaks May–October, especially in the north), Cambodia (May–October), Laos (June – September), Vietnam (year-round; seasonal peaks May–October, especially in the north), Malaysia (year-round transmission; peak Oct–Dec in Sarawak), Indonesia (year-round; peak season varies by island; Bali year-round), and the Philippines (unknown; probably year-round). (JE also occurs occasionally in Japan, Taiwan, Singapore, Hong Kong, Eastern Russia, Guam, Saipan, and Brunei Darussalam during the wet and early dry seasons. More recently JE has become established in Papua New Guinea and the Torres Strait Islands, with the occasional case in Northern Australia.)
How you can prevent JE
For those travellers who feel they may be at risk or wish to have the additional protection of immunisation against JE, two vaccines are available to Australian travellers.
Imojev – The newest vaccine is a single-dose vaccine suitable for adults and infants/children 12 months and older. It provides 94% protection after 14 days. Because the vaccine is new, a booster dose is not recommended at this stage.
Jespect – 2 intramuscular doses a month apart. Although it is registered for use in Australia for persons 18 years and older, it is also suitable for infants/children 12 months and older, if the alternative vaccine Imojev is contraindicated. Information regarding boosting is limited, but a single booster dose may be recommended after 12 months, if the risk of exposure continues.
Read more about these vaccines, the schedules, protection levels, and potential side effects.
AVOID MOZZIE BITES
In any tropical region, preventing insect bites is vital – especially as malaria, dengue fever, Chikungunya fever, and other insect-borne diseases are even more likely to be present. Here are some simple bite-prevention measures you can take:
- Apply mosquito repellent containing an effective active ingredient, such as DEET, Picaridin, IR3535, or oil of lemon eucalyptus to all exposed skin when outdoors.
- Wear protective clothing (loose-fitting, long-sleeved shirts and long pants).
- If possible, staying indoors at twilight and after dark.
- Sleep under a mosquito net impregnated with Permethrin or Deltamethrin (which are available from Travelvax clinics), particularly if your accommodation does not have insect screens or air conditioning.
- Use mosquito coils and knock-down aerosol insecticides, if needed.
Learn more about protecting yourself against insects.
For more healthy pre-travel advice, call Travelvax Australia's free, no-obligation travel health advisory service on 1300 360 164.