A Victorian man in his 60s who’d holidayed in Phuket, Thailand in early May died this week from Japanese encephalitis (JE) in a Melbourne hospital.
The traveller was on a 13-day trip to Thailand and stayed at a local resort. On day 8 of his trip, he suddenly became lethargic, however continued his travels to Bangkok 2 days later. While in Bangkok he remained lethargic, slept for several hours each day, had a poor appetite and was sweaty. He flew back to Victoria on Day 13 of his trip and presented to a local hospital a day later suffering from confusion. The following day, due to his deteriorating mental state and lethargy, he was placed on a ventilator and transferred to the Royal Melbourne Hospital. The diagnosis of JE occurred on day 22 of his illness after blood tests confirmed the presence of the virus - details of the traveller’s itinerary indicated that he hadn’t visited rural areas, however multiple mosquito bites were noticed. (This information is reported in Promed, on behalf of the Victorian Institute of Infectious Disease Service, the Royal Melbourne Hospital and the University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia.)
On the face of it, the man in his 60s wasn’t at a great risk of contracting this viral disease. He had a typical short stay: just over a week at a resort in Phuket and then a return trip via Bangkok to Victoria. We’re told he didn’t spend any time in rice-growing areas, where most JE outbreaks occur. (Wading birds in rice fields and pigs serve as reservoirs, or ‘amplifying hosts’, in the virus’ transmission cycle. Mosquitoes transfer it between the two animal species before passing it on to humans who are termed ‘dead-end hosts’ because we are unlikely to have enough virus in the blood that a mosquito could ingest and then transmit to others.)
JE cases are very rare
Promed has previously reported on a case of JE originating from Thailand and, while it is an unusual occurrence in short-term travellers to Thailand, the disease actually is endemic there. This recent case is now the second recorded in Victoria, after another man was hospitalised in February 2015 following a stay in Canggu on the Indonesian island of Bali. It appears the Melbourne man did not seek any pre-travel health advice prior to travelling to Phuket.
The US Centers for Disease Control and Prevention (CDC) reports that for most travellers to Asia, the risk of JE is extremely low, with ‘the overall incidence of JE among people from non-endemic countries travelling to Asia estimated to be <1 case per 1 million travellers; however the degree of risk is based on the destination, length of stay, season of travel and activities.
Only 79 cases of JE among travellers or expatriates from non-endemic countries were reported to the CDC from 1973 through to 2015 – 10 of those were recorded after a vaccine became available in the United States in 1993. In Australia, since 2001 there have been 10 reported cases of JE – most of them in Cape York Peninsula and the Torres Strait Islands.
Rare, but potentially severe outcome
The Japanese encephalitis virus is an arbovirus and is closely related to other mosquito-borne viruses such as West Nile, St Louis encephalitis, yellow fever and dengue fever.
Most cases occur among local people living in rice-producing areas of China, the Indian subcontinent, and Southeast Asia. More recently JE has become established in Papua New Guinea and the Torres Strait Islands, with the occasional case in Northern Australia.
Most JE infections are mild: usually a slight fever and a headache. But, for around 1-in-100 victims, the infection is severe and statistics show that 20-30% of these patients will die while 30% - 50% will be left with a severe neurological disability.
Because so few returned travellers show signs of illness – unlike the unfortunate Victorian gentleman – the incidence of JE is almost certainly under-reported here and elsewhere around the world.
Those at higher risk of JE
Inevitably, cases like the Victorian one fuel the vaccination question: should short term travellers to Asian holiday resorts such as Phuket and Bali be vaccinated?
The fringes of holiday resort areas and major towns and cities in Asia often do have rice paddy fields and pigs (such as Canggu and Seminyak in Bali) – so, we shouldn’t be surprised that the JE virus is present in mosquitoes in these areas. All travellers to Asia (and other tropical regions) must be fully aware of the need to take appropriate measures to avoid mosquito bites.
Typically, the vaccine is recommended for backpackers passing through regional areas for more than a month, for rural-based aid workers, and expats living or working in an endemic region for extended periods, particularly during or just after the wet season.
The Australian Immunisation Handbook recommends that doctors consider advising vaccination for travellers in the following situations:
- JE vaccination is recommended for travellers spending 1 month or more in endemic areas in Asia and Papua New Guinea during the JE virus transmission season, including persons who will be based in urban areas but are likely to visit endemic rural or agricultural areas.
- The Handbook further advises that “it is important to note that, as JE has occurred in travellers after shorter periods of travel, JE vaccination should be considered for shorter-term travellers, particularly if the travel is during the wet season, or anticipated to be repeated, and/or there is considerable outdoor activity, and/or staying in accommodation without air conditioning, screens or bed nets”. Risk is negligible for short stay business travellers to urban areas.
The imperative of insect bite avoidance
So, should Australians planning to visit Thailand or anywhere else in Asia where Japanese encephalitis occurs be concerned? The answer is yes and no.
No, because for a traveller on a typical short holiday in Asia, the risk of getting JE is clearly so low that vaccination is very rarely recommended.
Yes, because the Victorian case demonstrates that no-one travelling to a tropical Asian destination – even well-travelled ones like Phuket - can afford to be blasé about avoiding mosquito bites. Not anywhere. Not any time.
And the repellent won’t just prevent JE: Dengue, Zika and chikungunya are a significantly higher risk for travellers in many tropical and sub-tropical destinations because they’re spread by the urban-breeding, daytime-feeding Aedes species.
Adopt some or all of these bite avoidance measures:
- Apply an insect repellent containing an effective ingredient such as DEET (30-50% formulations for adults, or 10-20% formulations for young children and infants as young as 2 months of age), Picaridin or preparations containing extract of lemon eucalyptus oil, as necessary when outdoors.
- Wear long, loose-fitting, light-coloured clothing after dark, particularly around dusk and dawn when JE (Culex) mozzies are most active. Treating your clothing with the contact insecticide permethrin creates a deadly barrier to mozzies and other bugs that can bite through light material.
- Sleep under a treated bed net, especially if you are staying in a tent or in budget accommodation without screened doors and windows, or air-conditioning. You can buy a treated net or purchase a DIY kit and use it to treat a net and clothing to give yourself a strong barrier against biting insects.
While the focus is still on a risk assessment and the full range of bite protection measures, the length of the trip is no longer the main consideration for vaccination. Increasingly, it is being discussed in terms of a long-term ‘investment’ in healthy travel, particularly for the more adventurous who regularly head off the beaten track in Asia, as well as those who expect to continue travelling there regularly for leisure or work and want the extra protection (and peace of mind) immunisation offers.
There are two very effective vaccines against Japanese encephalitis for those at sufficiently high risk to warrant that level of protection, or who are unsure of their itinerary and wish to be proactive. One of these vaccines (Imojev) affords protection for at least 5 years. Unfortunately these vaccines are more expensive than your typical travel vaccines so discuss the need for this and other vaccinations for your trip with an experienced travel medicine practitioner.
If this sounds like you, discuss the merits of vaccination with your travel doctor at least 6 weeks before departure.
Heading to Asia? Learn more about the risks of Japanese encephalitis and the potential travel health issues for your trip by calling the Travelvax Australia travel health advisory service on 1300 360 164 for the latest country-specific information.