Enteroviruses and Rhinoviruses

Picornavirus Overview - Tiny RNA Titans

⭐ Picornaviruses are small (pico, ~20-30 nm), non-enveloped viruses with a single-stranded, positive-sense RNA genome (+ssRNA) that acts directly as mRNA.

• Family: Picornaviridae (📌 Positive RNA virus).
• Structure: Naked virion, icosahedral capsid symmetry.
• Replication: Occurs entirely in the host cell cytoplasm.
• Transmission: Primarily fecal-oral (Entero-, Hepatovirus) or respiratory (Rhinovirus).
• Genera include: Enterovirus, Rhinovirus, Hepatovirus, Cardiovirus, Aphthovirus.

Enteroviruses - Gut & System Invaders

• Family: Picornaviridae; small, non-enveloped, (+)ssRNA viruses.
• Stability: Acid-stable (survive gastric passage).
• Transmission: Primarily fecal-oral; respiratory route also possible.
• Major Groups & Diseases:
  • Coxsackievirus A:
    • Hand, Foot, and Mouth Disease (HFMD) - vesicular rash.
    • Herpangina - pharyngeal vesicles/ulcers.
    • Acute Hemorrhagic Conjunctivitis (AHC).
  • Coxsackievirus B: (📌 B for Body involvement)
    • Pleurodynia (Bornholm disease/devil's grip) - severe chest pain.
    • Myocarditis, pericarditis.
    • Aseptic meningitis.
  • Echoviruses (Enteric Cytopathic Human Orphan):
    • Aseptic meningitis (common cause).
    • Rashes, febrile illnesses, respiratory infections.
  • Enterovirus D68 (EV-D68):
    • Severe respiratory illness, especially in children.
    • Associated with Acute Flaccid Myelitis (AFM).
• Lab Diagnosis: RT-PCR (CSF, stool, throat swabs), virus culture, serology.

⭐ Aseptic meningitis is a common neurological manifestation of non-polio enterovirus infections, particularly Coxsackieviruses and Echoviruses.

Poliovirus Focus - Paralysis Peril

• Transmission: Fecal-oral route.
• Pathogenesis: Infects oropharynx/gut → viremia → CNS invasion (anterior horn cells).
• Clinical Spectrum:
  • Asymptomatic (>90%).
  • Abortive (minor, non-specific illness).
  • Non-paralytic (aseptic meningitis).
  • Paralytic (<1%):
    • Asymmetric flaccid paralysis; sensation intact.
    • Spinal (commonest), bulbar, bulbospinal.
• Post-Polio Syndrome (PPS): New muscle weakness/pain decades later.
• Vaccines:
  • IPV (Salk, Killed): Serum IgG.
  • OPV (Sabin, Live): Serum IgG & intestinal IgA (mucosal immunity). 📌 Sabin = Secretory IgA + Spreads.

⭐ Inactivated Polio Vaccine (IPV, Salk) induces serum IgG but minimal intestinal IgA, while Oral Polio Vaccine (OPV, Sabin) induces both serum IgG and intestinal IgA, providing mucosal immunity and contact immunization.

Rhinoviruses - Common Cold Kings

• Picornaviridae family, Enterovirus genus (formerly Rhinovirus genus).
• (+)ssRNA, icosahedral, non-enveloped.
• Acid-labile (distinguishes from other enteroviruses).
• Over 160 serotypes; no cross-immunity.
• Transmission: Respiratory droplets, fomites.
• Primary cause of common cold (nasopharyngitis).
• Symptoms: Sneezing, nasal discharge, sore throat; usually afebrile.
• 📌 Mnemonic: RHINO = Respiratory, Hundreds (serotypes), Icosahedral, No Outside (envelope), Optimal temp 33°C.

⭐ Rhinoviruses replicate optimally at 33-35°C, corresponding to the cooler temperature of the upper respiratory tract, and their acid lability prevents gastrointestinal infection.

Lab & ID Clues - Viral Showdown

High‑Yield Points - ⚡ Biggest Takeaways

• Enteroviruses (Poliovirus, Coxsackie, Echovirus): RNA viruses, fecal-oral route; cause aseptic meningitis.
• Poliovirus: Paralytic poliomyelitis; Salk (IPV-killed) & Sabin (OPV-live) vaccines prevent.
• Coxsackie A: Causes Hand, Foot, and Mouth Disease (HFMD), herpangina.
• Coxsackie B: Causes myocarditis, pericarditis, pleurodynia.
• Rhinoviruses: Cause common cold; acid-labile (vs. enteroviruses); bind ICAM-1.
• Aseptic meningitis: common with Poliovirus, Coxsackie, Echovirus.
• RT-PCR for diagnosing enteroviral CNS infections.