Japanese encephalitis is an inflammation of the brain caused by an RNA virus belonging to the family Flaviviridae. The virus, which is spread by bloodsucking mosquitoes, is endemic to parts of Asia and is the leading cause of viral encephalitis in Asia.
Examples of areas where Japanese encephalitis is present are Japan, China, India, Bangladesh, Pakistan, Cambodia, Indonesia, Laos, the Philippines, Nepal, Thailand, Sri Lanka, Vietnam, the Korean peninsula, and eastern parts of Russia. Thank’sto widespread vaccination, the disease has declined sharply in Japan, South Korea and parts of China.
Japanese encephalitis is chiefly associated with agricultural environments, especially those where pigs are kept and where flood irrigation is practiced.
Transmission may take place year round, provided that the climate is suitable for mosquitoes. Rainy season (in the tropics) and warm season (in temperate climates) increase the mosquito population and thereby increase the risk of catching Japanese encephalitis
It is chiefly mosquitoes of the genus Culex that spread the disease. They can spread the disease between humans, and also between pigs and humans. Some bird species are also suspected of being able to serve as vectors for the Japanese encephalitis virus.
Vaccination against Japanese encephalitis
There is currently only one Japanese encephalitis vaccine licensed for use in the United Kingdom. It is an injectable vaccine approved for adults and for children from the age of 2 months.
Vaccination against Japanese encephalitis is especially important if:
- You will be visiting wet rural areas in a high-risk country, e.g. rice fields or marshlands.
- You will be in close vicinity of pigs in a high-risk country.
- You will visit a high-risk country during the rainy season.
- You will spend a lot of time outdoors in a high-risk country, e.g. camping, hiking or biking.
- You work in a laboratory or similar where you may be exposed to the virus.
To obtain more information about where to obtain your Japanese encephalitis vaccination, contact your GP or practice nurse.
Japanese encephalitis vaccination is usually not available for free on the NHS.
The cost can vary a lot between clinics, and each dose can cost more than £90.
The vaccine is injected.
Small children are injected in the leg, while older children and adults are injected in the upper arm.
Two doses are given, with 28 days between the first and second dose.
If you are in a hurry, you can receive the second dose 7 days after the first dose, but only if you are in the age span 18 – 65 years.
Ideally, get the second dose at least 7 days prior to visiting a region where you may encounter Japanese encephalitis
To facilitate this, it is advisable to contact your GP or practice nurse at least 8 weeks prior to departure to schedule the two injections.
The vaccine provides protection for over 90% of those who receive two doses.
There is no guarantee that you will obtain full coverage, so protecting yourself against bloodsucking mosquitoes is still recommended.
To stay protected, get a booster dose of the vaccine 1-2 years after the initial vaccination.
Side effects of Japanese encephalitis vaccination
Examples of common side effects of Japanese encephalitis vaccination
- Redness, swelling and tenderness at the injection site
Examples of rare side effects of Japanese encephalitis vaccination
- Swollen face
- Difficulty breathing
Should I avoid Japanese encephalitis vaccination?
- Vaccination against Japanese encephalitis is not recommended for children younger than 2 months.
- Vaccination against Japanese encephalitis is not recommended if you have had a severe allergic reaction to any of its ingredients in the past.
- If you have a fever, the vaccination may need to be postponed.
- If you are pregnant or breastfeeding, talk to your GP to discuss your options when it comes to vaccination against Japanese encephalitis.
About Japanese encephalitis
The incubation period for Japanese encephalitis is normally 3-7 days, but reports exists of considerably longer incubation periods that exceeds two weeks.
A majority of those infected with the virus develop no symptoms or only mild symptoms.
Examples of symptoms:
There is no medical treatment that will kill the virus. Treatment is focused on mitigating the symptoms and handling the various problems that may occur while the body’s immune system fights the virus.
Among patients that develop serious symptoms of Japanese encephalitis, the death rate is approximately 25% even with hospital care.