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JEV (Japanese Encephalitis Virus) - IgM antibody-Serum
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Detects Japanese Encephalitis virus IgM.
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JEV (Japanese Encephalitis Virus) - IgM antibody-Serum
- Why is it done?
- Detection of Acute JEV Infection: This test detects IgM antibodies against Japanese Encephalitis Virus in serum, which indicates a recent or acute infection. IgM antibodies are the first antibodies produced by the immune system in response to JEV infection.
- Clinical Diagnosis of Encephalitis: Ordered when patients present with symptoms of meningoencephalitis such as fever, headache, neck stiffness, confusion, altered consciousness, seizures, and focal neurological deficits.
- Epidemiological Surveillance: Used for disease surveillance and confirmation during JEV outbreak investigations in endemic regions of Asia and Western Pacific.
- Timing of Testing: Performed ideally within the first 3-5 days of symptom onset when viremia is still detectable, and can be positive up to 2 weeks after illness onset. Most commonly positive in the second week of illness.
- Travel History Evaluation: Particularly useful for travelers returning from JEV endemic areas with compatible clinical symptoms.
- Normal Range
- Negative Result: Less than 1.0 IU/mL or reported as "Negative" or "Not Detected". This indicates absence of IgM antibodies against JEV and suggests no recent or acute JEV infection.
- Positive Result: Greater than or equal to 1.0 IU/mL or reported as "Positive" or "Detected". This indicates presence of IgM antibodies and confirms recent or acute JEV infection.
- Equivocal/Borderline Result: Results in the gray zone may require retesting or confirmation with additional serological tests. Different laboratories may have slightly different cutoff values.
- Units of Measurement: IU/mL (International Units per milliliter) or Qualitative (Positive/Negative) depending on the assay method used (ELISA, MAC-ELISA, or others).
- Clinical Interpretation of Normal: A negative result does not completely rule out JEV infection if tested within the first few days of illness, as IgM may not have developed yet. Repeat testing may be needed.
- Interpretation
- Positive IgM Result: Strong evidence of acute or recent JEV infection (typically within 2 weeks). IgM antibodies develop early in infection, usually appearing 3-5 days after symptom onset and lasting 30-90 days. This is the primary test for diagnosing acute JEV infection.
- Negative IgM with High Suspicion: If clinical suspicion remains high but IgM is negative, consider repeat testing 3-5 days later, or test IgG antibodies to assess for past or recent infection.
- Cross-Reactivity Considerations: IgM antibodies may show cross-reactivity with other flaviviruses (Dengue, West Nile Virus, Yellow Fever, Zika). Clinical history, epidemiology, and additional confirmatory testing (plaque reduction neutralization test or RT-PCR) help differentiate.
- Timing Matters: False negative results are common in the first 3 days of illness. IgM detection improves significantly from day 4 onwards and peaks around day 7-14. Early testing may require repeat sampling.
- Persistent Positivity: IgM can persist for months in some cases, potentially making it difficult to distinguish acute infection from recent past infection. IgG testing provides additional temporal information.
- CSF vs Serum: CSF IgM is more specific for CNS infection than serum IgM, as CSF IgM production indicates intrathecal antibody synthesis. Serum IgM may also be positive in uncomplicated viremia without CNS involvement.
- Immunocompromised Patients: IgM response may be delayed or diminished in immunocompromised individuals. Additional testing methods may be necessary.
- Associated Organs
- Primary Organ Systems: Central Nervous System (CNS) - brain and spinal cord are primary targets; also affects the meninges and can involve peripheral nerves.
- Japanese Encephalitis (JE): A potentially fatal form of encephalitis characterized by inflammation of the brain, presenting with fever, headache, altered consciousness, seizures, focal neurological deficits, and behavioral changes. Mortality rate ranges from 5-40%.
- Meningitis: Inflammation of the meninges (protective membranes around brain and spinal cord), causing fever, neck stiffness, headache, photophobia, and nausea.
- Complications: Long-term sequelae including cognitive impairment, motor disorders, seizure disorders, psychiatric manifestations, movement disorders (Parkinsonian features), and permanent neurological damage in survivors.
- Secondary Organ Involvement: Respiratory system (acute respiratory distress syndrome), cardiovascular system (myocarditis, arrhythmias), renal dysfunction, and hepatic involvement can occur in severe cases.
- Risk of Fatality: Case fatality rates are significant, particularly in symptomatic cases that progress to encephalitis. Age extremes (very young and elderly) have higher mortality.
- Asymptomatic Infections: For every symptomatic case, approximately 20-300 infections are asymptomatic or cause mild febrile illness without neurological involvement.
- Follow-up Tests
- JEV IgG Antibody: Recommended to confirm diagnosis and assess immune response. IgG develops after IgM and persists long-term. Rising titers between acute and convalescent sera confirm recent infection. Helps distinguish recent from past infection.
- JEV RT-PCR (Reverse Transcription PCR): Detects viral RNA in serum or CSF, particularly useful in early acute phase (first 5-7 days). More specific than serology but less sensitive in later stages of illness.
- Plaque Reduction Neutralization Test (PRNT): Gold standard confirmatory test that differentiates JEV from other flaviviruses. Demonstrates functional neutralizing antibodies and provides serotype information. Usually reserved for reference laboratories.
- CSF Analysis: Lumbar puncture with CSF examination for pleocytosis, protein elevation, and CSF IgM/IgG antibodies. CSF findings more specific for CNS involvement than serum. MAC-ELISA on CSF is preferred confirmatory test.
- Neuroimaging (MRI/CT): Brain MRI may show characteristic lesions in thalamus, basal ganglia, brainstem, and spinal cord. Helps assess severity and rule out alternative diagnoses.
- Other Flavivirus Serology: Dengue, West Nile Virus, Zika, and Yellow Fever IgM/IgG antibodies may be needed to exclude cross-reactivity, especially in endemic regions.
- Complete Blood Count (CBC): Monitors for hematological complications, thrombocytopenia, and leukopenia which can occur in severe cases.
- Biochemical Profile: Liver function tests, renal function, electrolytes to assess organ involvement and guide supportive care management.
- EEG (Electroencephalography): May show abnormalities in cases with seizures or altered consciousness. Helps monitor seizure activity and brain function.
- Repeat Testing: If initial IgM is negative but clinical suspicion remains high, repeat serum testing 3-5 days later or obtain CSF sample for MAC-ELISA.
- Fasting Required?
- Fasting Requirement: NO - Fasting is NOT required for JEV IgM antibody serum test.
- General Patient Preparation: Standard blood draw precautions apply. Patient can eat and drink normally. No special medication restrictions specifically for this test.
- Sample Collection Timing: Blood can be collected at any time of day. However, timing relative to illness onset is critical - ideally collected during 2nd week of illness when IgM is most likely to be positive.
- Special Instructions: Inform healthcare provider of recent travel to JEV endemic areas, exact date of symptom onset, and any recent vaccinations. This information aids interpretation.
- Medications: Continue all regular medications unless otherwise directed by physician. No medications need to be discontinued for this specific test.
- Sample Type: Serum sample collected in standard sterile venipuncture tube. Typically 3-5 mL of blood. Store at 2-8°C if there is a delay in processing.
- After Testing: No restrictions after blood draw. Patient may resume normal activities immediately. Rare complications include minor bleeding or bruising at puncture site.
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