Japanese encephalitis


The Japanese encephalitis is the most important viral infection of the brain in Asia. It is caused by the Japanese Encephalitis virus. So far there are no effective medicines for the disease. Vaccination is therefore the best prevention besides effective protection against mosquito bites. Read here everything important about Japanese Encephalitis, its symptoms and preventive measures.

ICD codes for this disease: ICD codes are internationally valid medical diagnosis codes. They are found e.g. in medical reports or on incapacity certificates. A83G04Article ReviewJapanese Encephalitis

  • description
  • symptoms
  • Causes and risk factors
  • Examinations and diagnosis
  • treatment
  • Disease course and prognosis

Japanese Encephalitis: description

Japanese Encephalitis is an inflammation of the brain that is triggered by a virus. Every year, around 50,000 people contract Japanese encephalitis, and around 15,000 people die as a result. A vaccine is the best prevention against the disease.

Over half of the world's population is at constant risk of infection with the Japanese Encephalitis virus. This affects more than four billion people in 25 countries.

If the central nervous system (brain or spinal cord) is affected by the Japanese Encephalitis virus, mortality is very high. A significant proportion of diseased patients also suffer neurological sequelae. However, not everyone infected develops Japanese Encephalitis. Only one in 25 to 100 infected people will actually get sick. In the milder cases, the infection often goes unnoticed with only mild symptoms.

Particularly affected are children and the elderly. In endemic areas, especially the three- to six-year-olds are affected. In under three year olds, the disease rarely occurs.

Japanese encephalitis: incidence and risk areas

Japanese encephalitis occurs mainly in South Asia. The Japanese Encephalitis virus is spreading more and more. Meanwhile, the virus has also appeared in northern Australia. The reason for this is probably the bird migration, increasing irrigation, animal smuggling and global warming.

In the past, epidemics mainly affected Southeast Asia and India. Despite vaccination - Japanese encephalitis remains the most common brain virus infection in Asia. About every ten years, it occurs in the form of epidemics.

Outbreaks occur in the northern, temperate climatic region, particularly between May and October (Japan, Taiwan, China, Korea, North Vietnam, northern Thailand, Bangladesh, northern and central Burma, Nepal, maritime Siberia and northern India, among others). In southern tropical regions (including South Vietnam, southern Thailand, Indonesia, Malaysia, Philippines, Sri Lanka, and southern India), infection is relatively uniform throughout the year. A high point of the infection rate is there especially at the beginning of the rainy season, which lasts from May to October.

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Japanese Encephalitis: Symptoms

In children and the elderly, the disease is usually very clear. Often, however, the disease is so mild that it is overlooked.

About 5 to 15 days after the infection by a mosquito bite, the first symptoms of Japanese encephalitis appear. First, the virus multiplies in the skin and lymph nodes. Various tissues such as muscle or glandular tissue may additionally be affected. At this stage, the symptoms are similar to a flu. Especially in children, gastrointestinal complaints are also common.

After two to four more days, neurological symptoms develop. This is the time when the virus reaches the brain. The consciousness can be massively disturbed up to comatose states. It can lead to paralysis and convulsions. Japanese encephalitis may be similar to Parkinson's disease due to tremor, muscle stiffness and gait disturbances. Also symptoms of meningitis are common. The symptoms occur depending on the affected brain area.

Particularly serious is the inflammation in the brainstem. From there, vital functions such as breathing and circulation are controlled. If the regulatory centers are disturbed, it can cause serious complications. The more severe the course, the lower the probability of survival and the higher the risk of long-term damage.

Later, the symptoms slowly recede. Diseased individuals who have suffered from inflammation in the brain or spinal cord often do not completely reverse the symptoms. The long-term consequences mainly include neurological and psychiatric disorders. Late effects can still occur after years. Without treatment, Japanese Encephalitis can be fatal.

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Japanese encephalitis: causes and risk factors

The cause of Japanese encephalitis is the Japanese Encephalitis virus (JEV). It belongs to a virus family (Flavivirus) that is spread all over the world. This family also includes the West Nile virus, the yellow fever virus or the early-summer encephalitis (FSME) virus.

The Japanese Encephalitis virus is found mainly in birds and pigs. In these animals the pathogen is often highly concentrated in the blood, so that the viruses can spread well. The animals usually do not get sick. The Japanese Encephalitis virus circulates between birds and mosquitoes. The human is then infected with the Japanese Encephalitis virus by a sting of the nocturnal rice field mosquito (Culex tritaeniorrhynchus).

Indigenous people often live in simple conditions in the countryside, where there is intensive contact with animals. However, a human-to-human transmission is not possible. In regions where Japanese Encephalitis is prevalent year round, many residents have experienced an often asymptomatic infection, developing antibodies to the virus.

There is a particularly high risk of infection in humid areas where optimal breeding conditions for the rice field mosquito, the transmitter of Japanese encephalitis, exist. In addition to the monsoon season and periods of particularly intensive irrigation, as they may be necessary on rice fields, are dangerous. Regions with stagnant water and warm temperatures provide optimal propagation conditions for the Japanese Encephalitis virus. This mainly affects rural areas. In the rainy season there are more and more outbreaks. In addition to moisture, a decisive factor is a permanent temperature above 20 ° C.

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Japanese encephalitis: examination and diagnosis

The virus can be detected in the blood and cerebrospinal fluid (cerebrospinal fluid). However, this is not easy. The evidence succeeds especially in the early disease phase, before the brain is affected. At this time, the symptoms are usually still unspecific. When the virus reaches the brain, it is often difficult to detect in the blood.

At about the tenth day of the disease, antibodies to the virus can be found in the blood. In most cases, the diagnosis for these antibodies is sought.

As soon as possible other causes of brain inflammation must be excluded and the correct diagnosis made. This prevents that other, treatable causes such as bacterial infections are overlooked and the start of treatment is delayed.