Brief overview
- What is Japanese encephalitis? An inflammation of the brain caused by a virus, which is particularly common in South-East Asia.
- Causes: Japanese encephalitis viruses, which are transmitted by blood-sucking mosquitoes
- Symptoms: usually no or only mild symptoms such as headaches and fever, in children mainly gastrointestinal complaints. Rarely severe courses with symptoms such as high fever, stiff neck, seizures, paralysis, loss of consciousness and even coma.
- Diagnosis: Detection of specific antibodies against the Japanese encephalitis virus in the blood or cerebrospinal fluid (CSF)
- Treatment: only symptomatic treatment possible (alleviation of symptoms); intensive medical care if necessary
- Prognosis: 1 in 250 infected people become seriously ill. Up to 30 percent of those affected die. 20 to 30 percent of survivors suffer permanent consequential damage (such as paralysis).
Japanese encephalitis: Description
Japanese encephalitis is an inflammation of the brain caused by a virus. There is a risk of infection mainly in South-East Asia and the western Pacific region, and therefore for more than three billion people.
Japanese encephalitis: Occurrence and risk areas
The risk areas for infection with Japanese encephalitis range from East Asia (e.g. Eastern Siberia, Korea, Japan) to Southeast Asia (Thailand, Vietnam, Cambodia, Philippines, Indonesia, etc.) and South Asia (India, Nepal, etc.). In the Western Pacific region, you can also contract the Japanese encephalitis virus in Papua New Guinea, for example. And the viral disease even occurs at the northern tip of Australia.
In the temperate climate zone of Asia, Japanese encephalitis can be contracted particularly in summer and fall. In tropical-subtropical regions, the greatest risk of infection is during and after the rainy season. However, it is generally possible to become infected with the Japanese encephalitis pathogens in these areas all year round.
Japanese encephalitis: symptoms
Four to 14 days pass between infection and the first symptoms appearing (incubation period). However, most infected people develop no symptoms at all or only mild symptoms similar to those of a flu-like infection (such as fever and headache). In children with Japanese encephalitis, abdominal pain and vomiting can be the main initial symptoms.
- high fever
- headache
- stiff neck
- Sensitivity to light
- Disturbance of movement coordination (ataxia)
- Trembling (tremor)
- Impaired consciousness up to coma
- seizures
- Spastic paralysis
These severe symptoms of Japanese encephalitis can be explained by the spread of the infection to the central nervous system: an inflammation of the brain (encephalitis) develops, which can subsequently spread to the meninges (combined inflammation of the brain and meninges = meningoencephalitis). Additional inflammation of the spinal cord is also possible (meningomyeloencephalitis).
Such a severe course of Japanese encephalitis is often fatal or leaves neurological and psychiatric sequelae. These include, for example, signs of paralysis, repeated seizures or loss of the ability to speak.
Japanese encephalitis often takes a severe course, especially in young children and older people.
Japanese encephalitis: causes and risk factors
Japanese encephalitis is triggered by the Japanese encephalitis virus (JEV). It belongs to the so-called flaviviruses. Other members of this virus family include the West Nile virus, the yellow fever virus and the causative agent of tick-borne encephalitis (TBE).
Unlike infected pigs or waterfowl, the amount of virus in the blood of infected humans can never increase to such an extent that healthy mosquitoes become infected during a blood meal and thus become a risk of infection for other people.
There is an increased risk of contracting Japanese encephalitis, especially for the population in rural and peri-urban areas in the risk regions mentioned above. In these areas, people usually live in close proximity to the host animals of the pathogen (pigs, waterfowl).
Japanese encephalitis is particularly common in regions with extensive rice cultivation and/or pig farming. Rice-growing areas play a role because the humid environment provides optimal breeding conditions for the main vectors of the disease – the rice field mosquitoes. Humidity is also the reason why outbreaks of the disease are often more frequent during the rainy season and afterwards – a lot of stagnant water combined with a warm climate provide ideal conditions for the Japanese encephalitis virus to spread.
Japanese encephalitis: examination and diagnosis
At the same time, other possible causes for the brain inflammation (e.g. other viruses, bacteria) must be ruled out with suitable examinations. This prevents other, treatable causes such as bacterial infections from being overlooked.
Japanese encephalitis: treatment
To date, there is no targeted, i.e. causal, therapy for Japanese encephalitis. The disease can only be treated symptomatically, i.e. by alleviating the patient’s symptoms. For example, the doctor can administer anticonvulsants to the patient.
Japanese encephalitis is often treated in the intensive care unit. If necessary, a poor general condition can be better stabilized there. Above all, the intracranial pressure must be closely monitored and possibly reduced (encephalitis can cause the brain to swell dangerously!).
Japanese encephalitis should be treated as quickly and carefully as possible. This increases the patient’s chances of survival and reduces the risk of secondary damage.
Japanese encephalitis: course of the disease and prognosis
Japanese encephalitis: Vaccination
Anyone planning a trip to an area where Japanese encephalitis is widespread can protect themselves from infection with a vaccination. The available vaccine can be injected from the age of 2 months. Two vaccine doses are required for effective protection. They are normally administered 28 days apart.
For adults up to the age of 65, there is also the option of a faster vaccination schedule, for example for trips to Asia planned at short notice. In this case, the second vaccination dose is given seven days after the first.
You can find out more about the administration, effectiveness and possible side effects of this vaccination in the article Japanese encephalitis vaccination.
Japanese encephalitis: other preventive measures
In addition to the vaccination, there is another way to prevent infection with the Japanese encephalitis virus – by carefully protecting yourself from mosquito bites:
The Culex mosquitoes that transmit the Japanese encephalitis virus are mainly active in the evening and at night. During this time, you should therefore take particular care to protect yourself from mosquito bites if you are in a risk area. Important tips:
- Use a suitable mosquito repellent.
- Sleep under a mosquito net to keep the carriers of Japanese encephalitis away from you at night.
