Herpes Simplex Virus Infections

HSV Basics - Viral Villains Unveiled

• Family: Herpesviridae (Subfamily: Alphaherpesvirinae).
• Types & Primary Tropism:
  • HSV-1 (HHV-1): Typically orofacial; latency in trigeminal ganglia.
  • HSV-2 (HHV-2): Typically genital; latency in sacral ganglia (S2-S5).
  • Note: Significant site crossover occurs.
• Structure: Enveloped, icosahedral capsid, linear double-stranded DNA genome.
• Transmission: Direct contact with active lesions, mucosal surfaces, or infected secretions (saliva, genital fluids). Vertical transmission possible during childbirth.
• Lifecycle Hallmark:
  • Primary infection → Local replication → Retrograde axonal transport to sensory ganglia → Lifelong Latency → Reactivation (triggers: stress, UV light, fever, immunosuppression) → Anterograde transport → Recurrent mucocutaneous lesions.

⭐ HSV establishes lifelong latency within sensory nerve ganglia, specifically the trigeminal ganglion for HSV-1 and sacral ganglia for HSV-2. This is a key characteristic enabling recurrent infections.

Clinical Picture - Rash Decisions

• Primary Orolabial (HSV-1):
  • Gingivostomatitis: Painful vesicles, erosions on oral mucosa, gingiva, lips. Fever, malaise. Children (6m - 5y).
• Recurrent Orolabial (HSV-1):
  • Herpes labialis ("cold sore"): Grouped vesicles on vermilion border. Prodrome: tingling, burning.
• Primary Genital (HSV-2 > HSV-1):
  • Painful vesicles, pustules, erosions on genitalia. Systemic: fever, myalgia, lymphadenopathy.
• Recurrent Genital:
  • Milder, shorter, localized. Prodrome common.
• Lesion Morphology:
  • Grouped vesicles on erythematous base ("dew drops on rose petal").
  • Vesicle → pustule → ulcer → crust.
• Specific Sites/Forms:
  • Herpetic Whitlow: Painful HSV on fingers/toes. Healthcare workers.
  • Eczema Herpeticum: Widespread HSV in eczema. Severe, life-threatening.
  • Herpes Gladiatorum: Wrestlers, contact sports.
  • Erythema Multiforme: Post-HSV; target lesions.

⭐ Tzanck smear: Multinucleated giant cells, ballooning keratinocytes.

Diagnosis & DDx - Spotting the Suspect

Clinical suspicion: Grouped vesicles on erythematous base.

• Lab Confirmation:
  • Tzanck Smear: Multinucleated giant cells (MNGCs). (📌 Tzanck: All Nuclei Clubbed)
  • Viral Culture: Gold standard, but slow.
  • PCR: Rapid, highest sensitivity & specificity. Test of choice.
  • DFA: Detects viral antigens.
  • Serology (IgM/IgG): For primary infection, typing.

• Key DDx:
  • Herpes Zoster: Dermatomal.
  • Aphthous Stomatitis: Oral, no vesicles.
  • Hand, Foot, Mouth Disease: Typical distribution.
  • Impetigo: Honey-colored crusts.
  • Erythema Multiforme: Target lesions (often HSV-triggered).

⭐ Tzanck smear showing multinucleated giant cells is a classic, rapid diagnostic clue for HSV/VZV infections.

Treatment & Prevention - Calming the Chaos

• Antiviral Therapy (Cornerstone):

  • Acyclovir: Oral (Primary: 200mg 5x/day, 7-10d; Recurrent: 800mg TDS, 2d or 200mg 5x/day, 5d), IV, topical.
  • Valacyclovir: (Episodic: 500mg-1g BD, 3-5d) - ↑ bioavailability.
  • Famciclovir: (Episodic: 125-250mg BD/TDS, 5d).
  • Mechanism: Inhibit viral DNA polymerase.
  • Duration: Episodic (2-10 days based on drug/severity); Suppressive (long-term).

• Indications: Genital/Orolabial herpes, Keratitis, Neonatal HSV, Encephalitis.

• Supportive Care: Analgesia, hygiene.

• Resistant HSV: Foscarnet, Cidofovir (immunocompromised).

• Prevention:

  • Avoid triggers (stress, UV).
  • Barrier methods (condoms).
  • Suppressive therapy for >6 recurrences/year.
  • C-section if active genital lesions at term.
  • Patient education on asymptomatic shedding.

⭐ Acyclovir requires dose adjustment in renal impairment; it's a common exam question.

High‑Yield Points - ⚡ Biggest Takeaways

• HSV-1 typically causes orolabial herpes; HSV-2 primarily causes genital herpes.
• Primary infection often more severe; herpetic gingivostomatitis (HSV-1) is common in children.
• Virus establishes latency in sensory nerve ganglia, leading to recurrent outbreaks.
• Tzanck smear shows multinucleated giant cells & Cowdry A inclusions; PCR is gold standard.
• Acyclovir is the first-line antiviral treatment.
• Key complications: Eczema herpeticum (Kaposi's varicelliform eruption), herpes keratitis, herpes encephalitis.