Q. What is Varicella‑zoster virus (VZV)?
A.
- DNA virus, family Herpesviridae, subfamily Alphaherpesvirinae.
- Causes two clinical entities: chicken‑pox (varicella) and shingles (herpes zoster).
Q. How is VZV transmitted?
A.
- Inhalation of respiratory droplets from vesicular fluid or nasopharyngeal secretions.
- Direct contact with skin lesions.
Q. What are the main types/clinical forms of VZV infection?
A.
- Primary infection → varicella (chicken‑pox).
- Reactivation of latent virus → herpes zoster (shingles).
Q. Pathogenesis of Varicella (primary infection) – step‑wise
A.
- → Virus enters via nasal or oral mucosa.
- → Replicates in nasopharyngeal epithelium and regional lymph nodes.
- → Primary viremia spreads virus to liver, spleen, and skin.
- → Secondary viremia carries virus to dermal capillaries.
- → Virus infects epidermal keratinocytes → vesicle formation.
- → Cell‑mediated immunity (CMI) limits spread; antibodies appear after 7‑10 days.
Memory trick: “Nose‑Lymph‑Blood‑Skin – N‑L‑B‑S – the VZV travel route.”
Q. Clinical features of chicken‑pox (varicella)
A.
- Incubation 10‑21 days.
- Prodrome: low‑grade fever, malaise, headache, loss of appetite.
- Rash: maculopapular → vesicular → pustular → crusted; centripetal distribution, more on trunk and face; lesions at different stages together.
- Pruritus common.
- Lesions become umbilicated, clear fluid, later crust.
Q. Common complications of chicken‑pox (exam focus)
A.
- Bacterial superinfection of lesions → impetigo, cellulitis, scar formation.
- Pneumonia (especially in adults, smokers, immunocompromised).
- Encephalitis (rare, high mortality).
- Hepatitis, myocarditis.
- Reye’s syndrome (if aspirin given).
- Hemorrhagic varicella in immunosuppressed.
Q. Pathogenesis of Herpes Zoster (shingles) – step‑wise
A.
- → After primary infection, VZV establishes latency in dorsal root ganglion (DRG) sensory neurons.
- → Decline in cell‑mediated immunity (age >50 yr, HIV, steroids, malignancy) → viral reactivation.
- → Replication within the neuron → anterograde transport along sensory nerve to skin.
- → Inflammation of the nerve → neuropathic pain (pre‑eruptive).
- → Virus infects epidermis in the dermatome → vesicular rash limited to that dermatome (usually unilateral).
Memory rhyme: “Latent ganglion → immunity drops → virus hops → nerve stops → rash pops.”
Q. Clinical picture of herpes zoster
A.
- Prodrome: burning, tingling, itching in a band‑like distribution (1‑5 days).
- Eruption: grouped vesicles on erythematous base, confined to a single dermatome; may involve face (V1) → Hutchinson’s sign.
- Post‑herpetic neuralgia (PHN) – pain persisting >1 month, common in elderly.
- Complications: bacterial superinfection, ocular involvement (keratitis, uveitis), motor neuropathy, Ramsay‑Hunt syndrome (facial nerve palsy).
Q. Laboratory diagnosis of VZV infection
A.
- Direct fluorescent antibody (DFA) or Tzanck smear from vesicle fluid – shows multinucleated giant cells (not specific).
- Viral culture – Vero or human embryonic lung cells; takes 5‑7 days, low sensitivity.
- Serology: IgM positive in acute infection; rising IgG titre in convalescence.
- PCR (most sensitive) – detects VZV DNA in vesicular fluid, CSF, blood; useful for atypical or disseminated disease.
- In neonates or immunocompromised: quantitative PCR for viral load.
Q. Management of varicella (primary infection)
A.
- Healthy children: symptomatic treatment – antipyretics, calamine lotion, antihistamines for itching.
- High‑risk groups (adolescents, adults, immunocompromised, pregnant): oral acyclovir 20 mg/kg q8h (or valacyclovir) within 24 h of rash onset.
- Intravenous acyclovir for severe disease, pneumonia, encephalitis, or immunosuppressed.
Q. Management of herpes zoster
A.
- Antiviral therapy (acyclovir 800 mg q5h, valacyclovir 1 g TID, or famciclovir 500 mg TID) started within 72 h of rash.
- Analgesics: NSAIDs, opioids, gabapentin/pregabalin for neuropathic pain.
- Corticosteroids (optional) in selected cases to reduce acute pain and PHN.
- Ophthalmology referral if V1 involvement.
Q. Prevention strategies (exam point)
A.
- Live attenuated varicella vaccine (2 doses at 12‑15 months and 4‑6 years) – prevents primary infection, reduces complications.
- Recombinant zoster vaccine (Shingrix) – >90 % efficacy in >50 yr, given in two doses, safe in immunocompromised.
- Post‑exposure prophylaxis: varicella vaccine within 3‑5 days of exposure or VZIG for high‑risk contacts.
Q. Important exam‑type MCQ pointers
A.
- VZV latency site = dorsal root ganglion.
- Primary viremia → secondary viremia → skin lesions.
- PHN risk ↑ with age >60, severe acute pain, rash on trunk.
- Reye’s syndrome association = aspirin use in varicella.