Enteroviruses and parechoviruses

Picornavirus Overview - Tiny RNA Terrors

• Positive-sense, Icosahedral, Cytoplasmic replication, One RNA strand, Really small, Naked Avirus (📌 PICO-RNA).
• Structure: ss(+)RNA, linear, non-enveloped.
• Replication: Occurs entirely in the cytoplasm. Viral RNA acts directly as mRNA.
• Transmission: Primarily fecal-oral (Enteroviruses, Hepatovirus A) but also respiratory (Rhinovirus).
• Genera: Enterovirus (Poliovirus, Coxsackievirus, Echovirus), Rhinovirus, Hepatovirus.

⭐ All RNA viruses replicate in the cytoplasm EXCEPT for Influenza and Retroviruses (they replicate in the nucleus).

Pathogenesis & Transmission - The Fecal-Oral Freeway

• Primary Route: Fecal-oral (contaminated hands, water, food).
• Viral Properties: Acid-stable, allowing survival through gastric acid.

• Incubation Period: Typically 3-6 days.
• Shedding: Virus shed in stool for several weeks, promoting transmission even after recovery.

⭐ Enteroviruses are the #1 cause of aseptic meningitis. CSF analysis shows lymphocytic pleocytosis with normal glucose and no bacteria on Gram stain.

Enterovirus Syndromes - From Meningitis to Myocarditis

• Aseptic Meningitis: Most common manifestation.
  • CSF profile: ↑ lymphocytes, normal glucose, normal/↑ protein.
• Hand, Foot, and Mouth Disease (HFMD):
  • Causes: Coxsackie A16, Enterovirus 71.
  • Oral ulcers plus vesicular rash on palms, soles, and buttocks.
• Herpangina:
  • Cause: Coxsackie A.
  • Fever, sore throat, and vesicles on the posterior pharynx.
• Myocarditis & Pericarditis:
  • Cause: Coxsackie B.
  • Chest pain, dyspnea; can lead to dilated cardiomyopathy.
• Pleurodynia (Bornholm disease):
  • Cause: Coxsackie B.
  • Severe, unilateral pleuritic chest pain ("Devil's grip").

⭐ Coxsackie B is a major cause of viral myocarditis, which can progress to dilated cardiomyopathy and chronic heart failure.

📌 Mnemonic: Coxsackie A for Aphthous-like (Herpangina) & HAnd-foot-mouth. Coxsackie B for Body (Myocarditis, Pleurodynia).

Parechovirus Pointers - The Neonate's Nemesis

• Major cause of sepsis-like illness & fever in infants < 3 months.
• Presents with high fever, extreme irritability ("angry baby"), and tachycardia.
• Rash is typically absent, a key distinction from enteroviruses.
• Diagnosis: RT-PCR on blood, CSF, or respiratory samples.

⭐ CSF often shows no white blood cells (no pleocytosis) even with CNS infection.

Diagnosis & Management - Catch, Confirm, Comfort

• Catch (Clinical Dx): Aseptic meningitis, herpangina, Hand-Foot-Mouth Disease (HFMD), myocarditis.
• Confirm (Lab Dx):
  • CSF analysis: ↑ lymphocytes, normal glucose, normal/↑ protein.
  • Gold Standard: RT-PCR on CSF, stool, or respiratory samples.
• Comfort (Management):
  • Supportive care is the mainstay.
  • IVIG for severe cases (e.g., agammaglobulinemia, chronic meningoencephalitis).

⭐ Pleconaril is an investigational antiviral that inhibits viral attachment by binding to a hydrophobic pocket in the VP1 capsid protein.

High‑Yield Points - ⚡ Biggest Takeaways

• Enteroviruses are the #1 cause of aseptic meningitis; transmission is fecal-oral.
• Includes Poliovirus, Coxsackieviruses (A/B), and Echoviruses.
• Coxsackievirus A causes Hand, Foot, and Mouth Disease and herpangina.
• Coxsackievirus B is notorious for causing myocarditis, pericarditis, and pleurodynia (Bornholm disease).
• Poliovirus damages anterior horn cells, leading to asymmetric flaccid paralysis.
• Human Parechovirus (HPeV) can cause severe sepsis-like illness and meningoencephalitis in young infants.