Japanese encephalitis (JEV) Virus Infection
Japanese encephalitis (JEV) virus infection typically progresses through several clinical stages with a range of signs and symptoms:
Incubation Period
Usually 5 to 15 days after a mosquito bite, most infected people are asymptomatic.
Prodromal Phase
Nonspecific flu-like symptoms appear, such as sudden high fever, headache, malaise, fatigue, nausea, vomiting, and general discomfort. This phase lasts a few days, and many recover without further illness.
Acute Encephalitic Phase
In less than 1% of infected people, the virus invades the central nervous system, causing encephalitis.
Clinically, JE cases present signs and symptoms similar to encephalitis of any viral origin and cannot be distinguished for confirmation. However, JE can be suspected as the cause of encephalitis as a febrile illness of variable severity associated with neurological symptoms ranging from headache to meningitis or encephalitis. Symptoms can include high fever. Severe headache, neck stiffness, Seizures (fits), especially common in children, Confusion, disorientation, altered mental status, or coma, Muscle weakness or paralysis, Tremors and abnormal movements such as choreathetosis or parkinsonian-like symptoms, Behavioral changes or irritability, increased sensitivity to high light.
Sequelae and Outcome
About 20% to 30% of those with encephalitis die and
30% to 50% of survivors have long-term neurological complications, including
cognitive impairment, paralysis, deafness, emotional instability, or motor deficits.
Severe Cases
May progress rapidly to coma and death without supportive care.
In short, Japanese encephalitis manifests initially as mild flu-like symptoms in most but can progress to serious brain inflammation with seizures, paralysis, and death in a minority of cases, especially in children and vulnerable populations.
Epidemiology of Japanese Encephalitis in India
In India, the age groups most affected by JE vary subtly by region but generally fall within children and young adults.
- Children aged 1 to 15 years are the principal group affected in most endemic areas, with the highest burden often seen in ages 1 to 5 and 5 to 10 years. Infants under 1 year show the least incidence.
- In some highly endemic districts such as Assam, studies show that higher JE incidence is in the 31- to 60-year-old age group, followed closely by the 16- to 30-year-old group, indicating a broader adult vulnerability in certain regions.
- Historically, boys tend to be infected more than girls, possibly due to behavioral factors.
- Children engage in more outdoor play near paddy fields and piggery areas, increasing mosquito exposure from Culex vishnui vectors.
Laboratory Diagnosis of JEV
Several laboratory tests are available for JE virus detection, which include
Enzyme-Linked Immunosorbent Assay IgM-ELISA (MAC)
This is the most common and recommended method for laboratory confirmation. Detection of JEV-specific IgM antibody in cerebrospinal fluid (CSF) or serum confirms infection. If the initial test is negative and clinical suspicion remains, a second serum sample collected 7 to 10 days later can be tested. Cross-reactivity with other flaviviruses can occur, so confirmatory testing may be necessary.
Genome Detection—RTPCR
Reverse transcriptase polymerase chain reaction can detect viral RNA in serum, CSF, or tissues. It is highly specific test but requires good specimen timing as viremia
Virus Isolation
The virus can be isolated in cell cultures, tissue cultures like BHK-21 cells. IT is less commonly used due to technical complexity and biosafety requirements.
Other Serological Tests
Hemagglutination inhibition (HI), complement fixation test (CF), IgG, etc., are used mainly for epidemiological studies, surveillance, and differentiation from other flavivirus infections
Rapid Diagnostic Test
Newer rapid IgM detection methods based on dot ELISA or lateral flow immunoassays are being evaluated for field diagnosis, offering quick results without specialized equipment. CSF and serum samples should be collected early after symptom onset. Because IgM may not be detectable immediately.
Vaccine for Japanese Encephalitis
- The Central Research Institute, Kasuali, has developed the JEV vaccine indigenously.
- It is a mouse brain-killed vaccine, and three doses are required to produce primary immunization. Two doses are administered subcutaneously within a gap of 7 to 14 days, followed by a third dose any time after one month and before one year after the second dose. A booster is required after three years.
- Mouse brain technology has limitations in huge production beyond a few million.
- Tissue culture vaccines with feasibility of mass production are under various phases of development, standardization, and/or commercialization.
