Emerging Viral Infections

Intro to Emerging Viruses - Viral Villains Arise

• Emerging infections: Newly appeared in a population or rapidly ↑ incidence/geographic range.
• Re-emerging infections: Previously controlled, now ↑ again.
• Key Drivers:
  • Zoonotic spillover (animal to human).
  • Environmental: Climate change, deforestation.
  • Human behavior: ↑ Travel, urbanization, ↑ population density.
  • Microbial adaptation: Mutations, recombination.
• WHO R&D Blueprint: Prioritizes diseases (e.g., Disease X) needing urgent research.

  ⭐ Most emerging infectious diseases (EIDs) are zoonotic in origin (approx. 60-75%).

Arboviral Threats - Mosquito Mayhem

-   Family: Flaviviridae
-   Vector: *Haemaphysalis spinigera* (tick)
-   Key Clinical: Biphasic fever, headache, myalgia, hemorrhagic manifestations; neurological complications. 📌 Mnemonic 'Forest Fever Frights': Fever, Frontal headache, Fotophobia, Myalgia, GI.
-   Diagnosis: RT-PCR (early), Serology (IgM/IgG)
-   Prevention: Tick control, PPE, KFD vaccine

⭐ Zika virus infection during pregnancy is a significant cause of congenital microcephaly and can also trigger Guillain-Barré syndrome.

Zoonotic Spillover Stars - Beastly Bugs

• Nipah Virus (NiV)

  • Family: Paramyxoviridae
  • Reservoir: Fruit bats (Pteropus)
  • Intermediate Host: Pigs
  • Transmission: Bats/pigs (secretions) → humans; human-to-human (close contact). Contaminated date palm sap.
  • Clinical: Myalgia, altered sensorium, encephalitis (seizures, coma), ARDS. Fatality: 40-75%.
  • Diagnosis: RT-PCR (CSF, urine, throat swabs), serology (IgM/IgG).
  • Biosafety: BSL-4.

    ⭐ Nipah virus encephalitis often presents with segmental myoclonus and cerebellar signs.

• Highly Pathogenic Avian Influenza (HPAI) / Pandemic Influenza

  • Family: Orthomyxoviridae (Influenza A)
  • Reservoir: Wild aquatic birds (ducks, gulls for HPAI: H5N1, H7N9); Humans/swine (Pandemic: H1N1).
  • Transmission: Birds → humans (direct/indirect, aerosols); human-to-human (pandemic strains).
  • Clinical:
    • HPAI (H5N1): Severe respiratory illness, pneumonia, ARDS, cytokine storm. Mortality: ~60%.
    • Pandemic (H1N1): Flu-like; severe in risk groups. Rapid global spread.
  • Diagnosis: RT-PCR (respiratory samples), viral culture, rapid tests.

Hemorrhagic & Others - Crimson Alarms

• Crimean-Congo Hemorrhagic Fever (CCHF)
  • Family: Nairoviridae (Bunyavirales).
  • Vector: Hyalomma ticks; Reservoir: Domestic/wild animals.
  • Clinical: Sudden high fever, myalgia, headache, severe hemorrhage (petechiae, ecchymoses, GI bleeding), shock, multi-organ failure.
  • Dx: RT-PCR, IgM/IgG ELISA. Rx: Ribavirin (early), supportive care.
  • Mortality: High (10-40%).
• Chandipura Virus (CHPV)
  • Family: Rhabdoviridae.
  • Vector: Sandflies; Reservoir: Uncertain (suspected small mammals).
  • Clinical: Acute febrile illness, vomiting, altered sensorium, seizures, rapid encephalitis, coma, esp. children <15yrs.
  • Dx: RT-PCR (CSF, serum), IgM. Rx: Supportive. No specific antiviral.
  • Mortality: Very high in children (50-75%).
• Ebola Virus Disease (EVD) - VHF Principles
  • Prototype: Filoviridae. Pathogenesis: Immune dysregulation, endothelial damage, coagulopathy. Strict infection control crucial.

⭐ Chandipura virus (CHPV) causes acute encephalitis syndrome (AES) with high child fatality in Indian outbreaks.

High‑Yield Points - ⚡ Biggest Takeaways

• Nipah virus: Reservoir fruit bats; severe encephalitis; high mortality; human-to-human transmission.
• Zika virus: Aedes mosquito vector; linked to neonatal microcephaly, Guillain-Barré syndrome.
• Ebola virus: Filovirus causing hemorrhagic fever; high fatality; spreads via direct contact with body fluids.
• MERS-CoV: Reservoir dromedary camels; causes severe acute respiratory illness (SARI).
• SARS-CoV-2: Caused COVID-19 pandemic; respiratory transmission; targets ACE2 receptors.
• Avian Influenza (H5N1, H7N9): Zoonotic from birds; high human mortality; pandemic potential.