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Varicella Zoster Virus (VZV)

Medicine > Infection

Background knowledge 🧠

Definition

  • Varicella zoster virus (VZV) is a DNA virus belonging to the herpesvirus family.
  • Primary infection causes varicella (chickenpox); reactivation leads to herpes zoster (shingles).
  • Lifelong latent infection persists in the dorsal root ganglia.

Epidemiology

  • Varicella is highly contagious, with an attack rate of over 90% in susceptible individuals.
  • Peak incidence occurs in children aged 1-9 years.
  • Herpes zoster incidence increases with age and immunosuppression.
  • Vaccination programs have reduced incidence in some countries, but the UK does not have universal varicella vaccination.
  • Seroprevalence studies show over 90% of adults in the UK are immune to varicella.

Aetiology and pathophysiology

  • VZV is transmitted via respiratory droplets or direct contact with vesicular fluid.
  • The virus infects mucosal surfaces and spreads to regional lymph nodes.
  • Viraemia occurs 4-6 days after infection, leading to the characteristic vesicular rash.
  • Latent infection resides in dorsal root ganglia, with potential reactivation later in life.
  • Reactivation (herpes zoster) typically occurs in the setting of decreased cellular immunity.

Types

  • Varicella (chickenpox): primary infection, generalized vesicular rash.
  • Herpes zoster (shingles): reactivation, typically dermatomal distribution.
  • Zoster sine herpete: reactivation without rash, causing neuropathic pain.
  • Disseminated zoster: widespread rash, usually in immunocompromised patients.

Clinical Features 🌡️

Symptoms

  • Prodrome: fever, malaise, headache (more prominent in adults).
  • Pruritic vesicular rash, beginning on the face and trunk, spreading centrifugally.
  • Painful dermatomal rash in herpes zoster.
  • Neuropathic pain and allodynia may persist after the rash resolves (postherpetic neuralgia).
  • Systemic symptoms may include anorexia, fatigue, and myalgia.

Signs

  • Crops of vesicles, pustules, and crusted lesions at various stages.
  • Lesions first appear on the face and trunk, then spread to extremities.
  • In herpes zoster, rash is usually unilateral and follows a dermatome.
  • Vesicular lesions on the tip of the nose (Hutchinson’s sign) suggest trigeminal nerve involvement and risk of ocular complications.
  • Scarring and pigmentation changes may occur after lesions heal.

Investigations 🧪

Tests

  • Clinical diagnosis is often sufficient, especially in typical cases.
  • VZV PCR from vesicular fluid or lesion swabs is the gold standard for confirmation.
  • Serology (VZV IgM/IgG) may be used in atypical cases or for immunity testing.
  • Direct fluorescent antibody (DFA) testing and Tzanck smear can also be used.
  • Routine blood tests may show lymphopenia and mild transaminitis in severe cases.

Management 🥼

Management

  • Supportive care: hydration, antipyretics, antihistamines for pruritus.
  • Antiviral therapy (aciclovir, valaciclovir) recommended within 24 hours of rash onset in at-risk groups (e.g., immunocompromised, neonates, adults).
  • Analgesia (e.g., paracetamol, NSAIDs) for pain management in herpes zoster.
  • Post-exposure prophylaxis with varicella zoster immunoglobulin (VZIG) in high-risk contacts.
  • Vaccination (live attenuated) recommended for non-immune healthcare workers and susceptible individuals in specific cases.
  • Consider corticosteroids in severe or complicated herpes zoster to reduce inflammation.

Complications

  • Bacterial superinfection of skin lesions (common in children).
  • Varicella pneumonia (more common in adults and pregnant women).
  • Cerebellar ataxia and encephalitis (rare but serious).
  • Postherpetic neuralgia (chronic pain after herpes zoster, especially in elderly patients).
  • Ocular complications (e.g., keratitis, uveitis) in cases of ophthalmic zoster.
  • Disseminated disease in immunocompromised patients (e.g., encephalitis, hepatitis).

Prognosis

  • Varicella is generally self-limiting in healthy children, with full recovery expected.
  • Adults and immunocompromised patients are at higher risk of complications.
  • Herpes zoster can result in chronic pain and disability (postherpetic neuralgia).
  • Prompt antiviral treatment reduces the risk of complications and improves outcomes.
  • Vaccination and post-exposure prophylaxis can prevent severe disease.

Key Points

  • VZV causes chickenpox and shingles; serious complications can occur, especially in at-risk populations.
  • Early antiviral treatment and appropriate prophylaxis are crucial in managing severe cases and preventing complications.
  • Immunisation is not routine in the UK but is recommended in specific high-risk groups.

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Infection