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MI9.1-6 | Zoonotic, Opportunistic & Emerging Infections — PBL Case

CLINICAL SETTING

October 2024. Kozhikode Medical College, Kerala. Dr Anjali Menon, second-year resident in Internal Medicine, is preparing handover notes for the night shift when the charge nurse pages her urgently: Ward 4 has admitted three pig farmers from the same village within 48 hours, all with high fever, encephalitis, and respiratory distress. One of the night-shift nurses who had managed the first patient is now febrile and confused. The District Surveillance Officer has been informed. The State Rapid Response Team is en route. You are the Year-2 MBBS PBL group assigned to Dr Anjali's firm; she has asked you to work through the case and brief her on the microbiological differential, investigation plan, and infection control priorities before the surveillance team arrives.

Trigger 1: Initial Presentation

Patient 1: Mr Rajan, 48 years. Pig farmer, Malappuram district. Admitted Day 1 with 7 days of high fever (40.2°C), severe headache, myalgia, and a single episode of generalised tonic-clonic seizure en route to hospital. Examination: disoriented (GCS 12), neck stiffness absent, bilateral coarse crepitations in lower lung zones, BP 96/60 mmHg, heart rate 118/min. No skin rash, no eschar. Daughter (carer) reports that three of their pigs died 2 weeks ago after a neurological illness; fruit bats roost in mango trees adjoining the piggery. Patient 2 and 3: Similar presentations admitted within the next 48 hours from the same village.

DISCUSSION POINTS

  • What is your differential diagnosis for this cluster of encephalitic-respiratory illness in pig farmers with bat exposure? Rank your top 3 differentials by probability and justify each using the epidemiological and clinical clues.
  • What features of this outbreak — animal-human interface, bat roost proximity, pig deaths preceding human cases, and the nurse's illness — suggest this pathogen may have pandemic potential? Use the WHO/IUCN framework for emerging infections.
  • Which biological properties of your most likely pathogen explain why it can cross multiple species barriers (bat → pig → human) while maintaining pathogenicity in each host?
Click to reveal Trigger 2: Investigations and Escalating Concern (discuss previous trigger first!)

Trigger 2: Investigations and Escalating Concern

Investigations on Rajan (Day 2 of admission): CBC: WBC 4,200/µL (lymphocytes 1,100/µL), Hb 11.2 g/dL, platelets 88,000/µL. LFT: ALT 220 U/L, AST 310 U/L, total bilirubin 2.1 mg/dL. Renal: creatinine 1.8 mg/dL. ABG: PaO₂ 58 mmHg on 6L O₂. CSF (LP performed): opening pressure 240 mm H₂O, WBC 280 cells/µL (90% lymphocytes), protein 120 mg/dL, glucose 52 mg/dL (blood glucose 96 mg/dL). India ink: negative. CSF Gram stain: no organisms. Blood cultures: pending. RT-PCR of throat swab and CSF for a regional panel of respiratory and neurotropic viruses is sent to the National Institute of Virology (NIV), Pune. The nurse who cared for Patient 1 without full PPE is now admitted with fever and headache (Day 5 of exposure). State surveillance confirms 2 additional cases from an adjacent village.

DISCUSSION POINTS

  • Interpret the CSF findings and peripheral blood results. Which pattern of CSF abnormalities is consistent with viral (aseptic) meningitis/encephalitis rather than bacterial meningitis? What does the thrombocytopaenia suggest about the pathogen's mechanism?
  • Why is RT-PCR preferred over serology at this stage of illness for the suspected pathogen? Name the appropriate specimen types and the molecular targets the NIV laboratory would amplify.
  • The nurse's illness on Day 5 after unprotected patient care suggests human-to-human transmission. Under IHR 2005, what constitutes a Public Health Emergency of International Concern (PHEIC)? Does this cluster meet the criteria? What immediate notification steps should the State take?
Click to reveal Trigger 3: Diagnosis, Management, and Prevention (discuss previous trigger first!)

Trigger 3: Diagnosis, Management, and Prevention

Day 4: NIV Pune reports RT-PCR positive for Nipah virus (NiV) in Rajan's serum and CSF. The nurse's serum is also NiV-positive. The State government activates the Nipah containment protocol; the village is quarantined; a 21-day contact-tracing exercise has identified 147 contacts. Two pigs from the farm test NiV-positive on veterinary testing. The WHO India Country Office is briefed. Rajan's condition deteriorates; he requires mechanical ventilation. Patient 2 is improving with supportive care. Patient 3 develops ARDS. The RRT asks the medical team: 'Is there any specific antiviral therapy? What about post-exposure prophylaxis for the contacts?'

DISCUSSION POINTS

  • Outline the current evidence for specific therapy in Nipah virus encephalitis. Discuss monoclonal antibody therapy (m102.4 / ribavirin) — their mechanisms, evidence levels, and availability in India under compassionate use.
  • Design an infection control strategy for the hospital to prevent further nosocomial NiV transmission. Include: patient placement, PPE tiers for different staff categories, waste management, and post-exposure monitoring for 147 contacts.
  • The national One Health coordination team is asked to prevent future spillover events. Identify three intersectoral interventions targeting the bat–pig–human interface that could reduce NiV emergence in Kerala, linking each to a specific element of India's National Action Plan for emerging infectious diseases.

Group Task Assignments

Group 1: Virology and Pathogenesis

  • Prepare a 5-minute presentation on Nipah virus: taxonomy (Paramyxoviridae, Henipavirus), genome structure, mechanism of cell entry (ephrin-B2/B3 receptor), and why it is neurotropic and pneumotropic.
  • Compare the 1998–1999 Malaysia outbreak with the 2018 Kerala outbreak: differences in transmission dynamics, CFR, and containment strategies.

Competencies: MI9.5, MI9.1

Group 2: Diagnostics and Laboratory Response

  • Create a diagnostic algorithm for a suspected Nipah encephalitis case from the District Hospital level to NIV Pune: specimen collection (BSL-2 precautions), transport (Triple packaging, WHO P650), test selection (RT-PCR targets: N and M genes), and interpretation of results.
  • Explain why serology (ELISA IgM) may be negative in the first 5 days and how RT-PCR fills the diagnostic gap.

Competencies: MI9.3, MI9.5

Group 3: Infection Control and Clinical Management

  • Draft a ward-level infection prevention protocol for a confirmed Nipah case: PPE requirements (ABSL-4 equivalent full PPE), patient cohort placement, visitor restriction, body fluid handling, and post-mortem precautions.
  • Review the evidence for ribavirin and m102.4 monoclonal antibody therapy; draft a compassionate use request template for submission to the Ethics Committee.

Competencies: MI9.5, MI9.2

Group 4: One Health and Public Health Response

  • Map the NiV transmission network in this outbreak using an epidemiological link diagram (index case → animal source → human cases → secondary healthcare cases). Identify where One Health surveillance would have detected the signal earlier.
  • Review the Kerala State NiV Response Protocol (2018/2023) and identify three gaps this 2024 cluster revealed. Propose improvements using the IHR 2005 core capacity framework.

Competencies: MI9.5, MI9.6

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [MI9.5] What are the WHO criteria for classifying an infection as 'emerging' versus 're-emerging', and which biological and ecological factors drove Nipah virus emergence in Kerala?
  2. [MI9.1] How does Nipah virus achieve cross-species transmission from Pteropus bats to pigs to humans, and what receptor-level mechanisms determine host range?
  3. [MI9.3] What is the optimal diagnostic algorithm for Nipah encephalitis at each stage of illness (Days 1–5, Days 5–10, convalescent phase), and which specimens should be collected under what biosafety conditions?
  4. [MI9.2] Why are immunocompromised patients (HIV, transplant) at higher risk of severe NiV disease, and which specific immune defects drive this vulnerability?
  5. [MI9.6] How does India's One Health framework (National Action Plan for AMR and Emerging Infections) coordinate the veterinary, environmental, and human health response to a NiV outbreak, and what role does IHR 2005 play?