Japanese Virus Encephalitis

 

Japanese Virus Encephalitis

By

P.K.Ghatak, MD.

Japanese virus encephalitis (JVE) was originally known as Japanese B virus encephalitis when, in 1934, the scientist Hayashi isolated the virus from the monkey brain and named it Japanese B virus to distinguish this summer virus from other viruses. In 1871, an epidemic of encephalitis broke out in Japan, and most of the clinical and pathological features were documented during that time but the pathogen remained elusive. Many large and small epidemics happened since then in Japan and the neighboring countries. Japan claimed the virus originated in Malaysia peninsula, Malaysia thought the virus came from Indonesia. According to WHO, Japanese virus encephalitis is the most common viral encephalitis in Asia.

The virus:

JVE is an arbovirus, transmitted to humans by Culex mosquitoes. The wild water-birds, like heron and egrets, are a natural harbor; the domesticated water -birds are an important source and household pigs are an amplifying factor for the virus.

The viral particles are 50 nanometers in diameter and 11kb in length, the genome of the virus is composed of several copes of capsid C-protein and the host supply the lipid covering membrane.

The vector: Culex mosquito.

Clinical features: Incubation period varies from 4 to 14 days, usually 6 to 8 days.

Initial symptoms: Most cases remain asymptomatic or only develop mild symptoms. High fever, headaches, variable mental status, convulsions in children. Mutism and speech impairment, abnormal movements like dystonia, chrioathetoid movements and Parkinson disease like features point to more severe inflammation in the basal ganglion of the midbrain and cerebellum.

Complications: Children usually have worse outcome. In some endemics, the mortality is as high as 25 % . Those who recover, have significant leaning difficulties and ambulatory disorders,

Diagnosis: The virus is difficult to isolate or successfully grown in labs. EISA IgM antibody test is mostly relied upon for confirmation where there is clinical and laboratory findings are indicating of viral encephalo-meningitis.

Treatment: Symptomatic.

Prevention: Individual protection from mosquito bites. Vaccination prior to visiting endemics counties, specially visiting agricultural area with intention of staying 30 days or more. The vaccine usually protects 5 years. WHO says the vaccine is under utilized.

Vaccine: The JVE vaccine is made using mouse brain and expensive. Japan, Korea and Taiwan made compulsory childhood vaccine to its population and the illness is controlled in those counties.

People at risk:

India is top of the list of nations keeping records, the outbreaks follow monsoon rain and flooded rice fields where Culex mosquito breeds. All south Asian countries, pacific island countries and Australia have recorded JVE encephalitis.

In the USA:

Only passengers returning home from a visit of the endemic countries brought the disease with them. The total number was 13, giving an incidence of 1 in 1 million returnees.

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