What is Japanese encephalitis? How did it originate?
Japanese encephalitis is a mosquito-borne brain infection caused by the flavivirus. Believed to have originated in the Indonesia-Malaysia region, it was first identified in Japan during the late 19th century.
It is now recognised as the leading cause of viral encephalitis in South East Asia and the West Pacific regions. It is mainly found in rural areas where rice cultivation and pig farming are common.
What are the symptoms of Japanese encephalitis?
In most cases, people infected with the Japanese encephalitis virus don’t experience symptoms. However, symptomatic cases can be severe enough to require hospital treatment and can result in brain damage or death.
According to the World Health Organization (WHO), up to 30 percent of cases of symptomatic Japanese encephalitis are fatal and 30 to 50 percent cause neurological disability.
Under one percent of people infected with Japanese encephalitis, around 1 in 250, will become ill, with symptoms appearing 5 to 15 days following infection. The mildest symptoms of Japanese encephalitis are fever and headaches.
More serious symptoms include nausea, convulsions and neck stiffness. As inflammation affects the brain, sufferers may experience confusion, become disorientated and fall into a coma.
How is Japanese encephalitis transmitted?
Japanese encephalitis cannot be spread from person to person. Instead, the disease is spread from infected wading birds, pigs and horses to humans via a mosquito carrying the virus.
When a Culex spp. mosquito feeds on an infected animal, it picks up the virus from its blood. The mosquito then passes the virus to humans by infecting our blood via its bite.
What is the transmission seasonality?
The transmission season of Japanese Encephalitis varies from place to place.
In some tropical areas, the disease is spread throughout the year, depending on farming practices.
In other tropical and subtropical areas, transmission season depends on rainfall and bird migration patterns.
In temperate zones, the spread is highest during summer months and in early autumn, from around May to September.
What are the infected areas in the world?
Japanese encephalitis is found in most countries in South and East Asia. 50 percent of cases occur in China, and it is endemic in 24 countries altogether. A more detailed map of countries in which the disease occurs is available on the CDC website.
What is a Japanese encephalitis certificate?
A Japanese encephalitis certificate is issued by a clinic to prove you have been vaccinated to protect yourself against contracting Japanese encephalitis.
Is Japanese encephalitis curable?
Japanese encephalitis is not curable. Treatment is available to deal with the symptoms of the disease and support the patient’s recovery.
How can you prevent Japanese encephalitis?
The most effective way to prevent Japanese encephalitis is by getting vaccinated before visiting a high risk area. .
Reducing your chances of being bitten by mosquitoes can also help lower the risk of contracting Japanese encephalitis.
Mosquitoes feed from dusk until dawn, so risk of infection during this period is the highest. Covering your skin adequately, treating your clothes with permethrin, applying insect repellent and sleeping under a mosquito net can all help prevent bites that cause infection.
How long before a trip do you have to get Japanese encephalitis vaccine?
The Japanese Encephalitis vaccine is given as a two-dose series, with the doses spaced 28 days apart.
However, the CDC indicates that as part of an accelerated schedule, adults aged 18–65 years can get the second dose as early as 7 days after the first dose. The last dose should be given at least 1 week before travel. In this case, the vaccination process should begin at least two weeks before travel.
A booster dose (third dose) should be given if a person has received the two-dose primary vaccination series one year or more previously and if there is a continued risk for infection or potential for reexposure.
For children, vaccination must begin at least five weeks before travelling to a high risk area, with protection effective seven days after the second (and final) jab.
Who should get the Japanese encephalitis vaccine?
The risk of contracting Japanese encephalitis for most travellers is very low, especially for short term travellers visiting urban areas.
However, if you are planning to stay a month or more in a high risk area during transmission season you are recommended to get the vaccine, especially if you will be visiting rural areas.
Even if your trip is shorter than one month, if you plan to spend any time in areas where rice cultivation or pig farming are common, you should get vaccinated.
If you plan to visit a country that is experiencing a Japanese encephalitis epidemic, you should get vaccinated before you go.
People working in close proximity of the virus, for example in a laboratory, are also advised to get vaccinated.
Who should not get the Japanese encephalitis vaccine?
The CDC recommends that the following groups of people do not get the Japanese Encephalitis vaccine:
- Anyone who has had a severe allergic reaction to the vaccine previously
- Anyone who has a severe allergy to any component of the vaccine
- Pregnant women
If you are pregnant, it’s best that you check with your health provider about whether the Japanese Encephalitis vaccine is suitable for you. If the risk of travelling unprotected to a high-risk region is significantly higher than the risk of receiving the vaccine, your health provider may recommend that you get the vaccine.
Getting vaccinated
- Minimum age for vaccination: The Japanese encephalitis vaccine can be given to children two months and above.
- How effective is it? The WHO states that the Japanese encephalitis vaccine is both safe and effective at preventing the disease.
- What are the side effects? Side effects are usually mild, and include redness, soreness and pain at the injection site, headache and muscle pain. In rare cases, you may experience hives and breathing difficulties.
- How many jabs are needed? The Japanese encephalitis vaccine is given in two jabs at least a week apart.
- How long does it last? A booster shot should be taken one to two years after the initial dose, and subsequent booster shots should be administered once every 10 years.
When and where was the last outbreak of Japanese encephalitis?
There are around 68,000 cases of Japanese encephalitis recorded worldwide every year. Outbreaks are regular, occurring every 2 to 15 years, particularly during rainy seasons when mosquito populations increase. Outbreaks have been linked to agricultural practices and intensive rice farming.
A number of countries have succeeded in overcoming epidemic rates of the disease through vaccination programs, but outbreaks still occur regularly in Cambodia, India, Malaysia, Myanmar, Nepal and Vietnam.
