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MI6.1-3 | Central Nervous System Infections — PBL Case
CLINICAL SETTING
It is the second week of August. The district hospital in Motihari, East Champaran district, Bihar, is overwhelmed. Over the past 10 days, 14 children from nearby villages have been admitted with acute febrile encephalitis. The monsoon has been heavy this year, and the surrounding paddy fields are flooded. You are a medical student on clinical posting. Your resident asks your PBL group to work through the next admission — a 9-year-old boy named Raju, brought in by his mother from a village 30 km away. The PHC referred him with a handwritten note: 'Fever 4 days, fits, unconscious since this morning.'
Trigger 1: Initial Presentation
Raju's mother, visibly exhausted, tells you: 'Pehle bukhar tha, phir raat ko haath paon kaampne lage, aur subah se uthta hi nahi' (First there was fever, then his limbs started shaking at night, and since morning he cannot be woken). On examination: temperature 39.8°C, pulse 116/min, BP 90/60 mmHg, RR 28/min, SpO₂ 94% on room air. GCS: E2V2M3 = 7/15. Pupils 3 mm bilaterally, equal, sluggishly reactive. Neck: stiff. No skin rash. No papilloedema on fundoscopy. Motor: bilateral upper limb spasticity. There are no focal neurological deficits. His immunisation card shows he received all NIS vaccines up to age 5, but his mother is unsure about the JE vaccine. The village ASHA worker accompanies them and mentions that two other children from the same village have similar symptoms and are still at home.
DISCUSSION POINTS
- Based on the clinical presentation (fever, seizures, altered consciousness, neck stiffness, no rash), construct a differential diagnosis listing at least 4 aetiologies in order of priority for a 9-year-old from rural Bihar in August. Justify your ranking.
- What features from the epidemiological context — season, geography, paddy fields, cluster of cases — point towards a specific aetiology? What is the microbiological mechanism by which this pathogen crosses the blood-brain barrier?
- The attending team debates whether to perform an LP before a CT head. The child has a GCS of 7/15. What are the clinical criteria for deferring LP? If LP is deferred, what immediate investigations and empiric treatment would you initiate?
Click to reveal Trigger 2: Investigations Unfold (discuss previous trigger first!)
Trigger 2: Investigations Unfold
A CT head is done: no mass lesion, no midline shift, cisterns patent, mild cerebral oedema. LP is performed. CSF results: opening pressure 230 mm H₂O, appearance clear, WBC 185/mm³ (88% lymphocytes), protein 82 mg/dL, glucose 52 mg/dL (blood glucose 88 mg/dL), RBC 4/mm³. Gram stain: no organisms. India ink: negative. ZN stain: negative. The CSF sample is sent to the state referral laboratory for JEV IgM MAC-ELISA. A blood smear for malaria is negative. Blood culture is sterile at 48 hours. Meanwhile, the state health department contacts the hospital: serological testing from the first 4 admitted children shows JEV IgM positive in 3 of 4 on MAC-ELISA of CSF. Raju's MAC-ELISA result returns: JEV IgM DETECTED in CSF.
DISCUSSION POINTS
- Interpret Raju's CSF in detail: appearance, cell count, glucose ratio (calculate it), protein. Which aetiological category does this pattern fit? How does it help exclude bacterial and tuberculous meningitis?
- Explain why JEV IgM MAC-ELISA on CSF is the gold standard for confirmation rather than serum IgM or RT-PCR on blood. What is the biological basis for the timing of IgM positivity (early vs late disease)?
- The treating team asks: 'Is there any specific antiviral therapy for Japanese encephalitis?' Answer this, and then outline the supportive management priorities for Raju, including management of raised ICP, seizure control, and airway protection.
Click to reveal Trigger 3: Diagnosis, Management, and Public Health Response (discuss previous trigger first!)
Trigger 3: Diagnosis, Management, and Public Health Response
Raju is diagnosed with Japanese encephalitis. He is managed in the ICU with IV mannitol, phenobarbitone for seizure control, IV fluids, nasogastric feeding, and intensive nursing care. His GCS improves slowly — by day 7, GCS 12/15, by day 14, he is awake but has residual left-sided weakness and cognitive slowing. The District Medical Officer visits and asks your team to prepare a rapid report on the outbreak: 14 confirmed JE cases, 2 deaths. The ASHA worker from Raju's village asks: 'Why are only children getting this? My husband works in the fields every day and he is fine.' The state public health officer wants to initiate vector control and vaccination. There is a Culex mosquito breeding site survey pending.
DISCUSSION POINTS
- Explain the epidemiological triad of Japanese encephalitis: the vector (Culex tritaeniorhynchus), the amplifying reservoir (pigs and wading birds), and the accidental dead-end host (humans). Why do rice paddy ecosystems amplify JE transmission? Why are children (not adult field workers) more vulnerable?
- Raju survives but has neurological sequelae. What are the common neurological sequelae of JE in survivors? From a microbiological standpoint, which host and viral factors determine the severity of CNS injury?
- The DMO asks you to recommend an evidence-based outbreak response. Outline: (a) the JE vaccine recommended for the endemic population in Bihar, (b) vector control measures targeting Culex breeding sites, and (c) criteria for case definition and surveillance reporting to the IDSP.
Group Task Assignments
Group 1: Microbiology and Diagnosis
- Prepare a table comparing the CSF patterns in bacterial, viral, tuberculous, and cryptococcal meningitis with appropriate column headers (appearance, pressure, WBC, differential, glucose ratio, protein, key test).
- Explain the MAC-ELISA principle: why does IgM capture ELISA give fewer false positives than indirect ELISA in JEV diagnosis?
Competencies: MI6.1, MI6.3
Group 2: Virology and Pathogenesis
- Map the JEV transmission cycle: Culex mosquito → pig/bird amplifying host → human dead-end host. Identify which stage produces the highest viraemia and why humans are dead-end hosts.
- Explain why JEV causes thalamic and basal ganglia lesions predominantly — relate to viral neurotropism and BBB crossing mechanism.
Competencies: MI6.2
Group 3: Public Health and Outbreak Response
- Outline the IDSP case definition for Acute Encephalitis Syndrome (AES) and the reporting workflow from PHC to state level during an AES outbreak.
- Compare the SA 14-14-2 live attenuated JE vaccine and the inactivated Vero cell-derived vaccine (JEEV): schedule, immunogenicity, cold chain requirements, and use in the Mission Indradhanush programme.
Competencies: MI6.2
Learning Issues
Research these questions and bring your findings to the discussion.
- [MI6.1] What are the major microbial causes of acute encephalitis syndrome in India by age group, and how does the epidemiological context (season, geography, exposure) guide the initial differential diagnosis?
- [MI6.2] What is the natural transmission cycle of Japanese encephalitis virus, and what host and environmental factors explain the seasonal clustering of cases in rice-paddy regions of India?
- [MI6.3] How is JEV IgM MAC-ELISA on CSF performed, interpreted, and distinguished from serum MAC-ELISA in terms of specificity and timing of positivity?