Varicella/Chickenpox

1. Etiology & Virology

• Caused by primary infection with human α-herpesvirus type 3 (Varicella-Zoster Virus, VZV).
• Following primary viraemia and cutaneous replication, VZV establishes lifelong latency in dorsal-root and cranial nerve ganglia.
• Reactivation (Herpes Zoster) occurs when cell-mediated immunity wanes.

2. Epidemiology

• Incubation period: 10–21 days (mean ≈ 14 days).
• Lifetime risk of reactivation (shingles) ≈ 30 %; increases with age (≈ 50 % by 85 years).

3. Transmission & Infectious Period

• Transmission: aerosolised respiratory droplets or direct contact with vesicular fluid.
• Infectious:
  • from 8–21 days post-exposure (extends to 8–28 days if VZIG given) and
  • from 2 days before rash onset until all vesicles are crusted.

4. Pathophysiology of Primary Varicella

Stage	Events	Clinical Correlate
Inoculation	Virus enters via nasopharyngeal/conjunctival mucosa	10–21 day incubation may have mild prodrome (fever, malaise)
Primary viraemia	Haematogenous spread to RES	Often asymptomatic
Secondary replication	Amplification in liver, spleen, RES (days 4–6)	Rising fever
Secondary viraemia	Seeding of capillary endothelium & epidermis → polymorphic vesicles	“Dew-drop on a rose petal” vesicles in crops at different stages
Immune containment	Humoral + cell-mediated responses → lesion crusting (by day 10)	Crusted lesions = non-infectious; virus transported to ganglia

5. Clinical Features

• Prodrome (variable):
  • fever
  • malaise
  • headache.
• Rash:
  • pruritic, polymorphic vesicles on erythematous base
  • lesions in successive “crops” on scalp, face, trunk, extremities, oral mucosa.
• Severity screening:
  • assess for high fever
  • respiratory distress
  • neurological signs
  • dehydration
  • extensive rash (> 20 lesions)
  • risk factors
    • age > 12 years unvaccinated
    • pregnancy
    • eczema
    • chronic lung disease
    • immunosuppression

6. Complications

• Skin & soft tissue:
  • secondary bacterial infection (GAS, S. aureus)
  • necrotising fasciitis.
• Respiratory:
  • viral pneumonitis
  • secondary bacterial pneumonia.
• Neurological:
  • acute cerebellar ataxia
  • encephalitis
  • aseptic meningitis
  • Guillain–Barré syndrome.
• Haematologic:
  • thrombocytopenia
  • purpura fulminans.
• Hepatic/metabolic:
  • hepatitis
  • Reye syndrome (with aspirin).
• Other:
  • arthritis
  • osteomyelitis
  • glomerulonephritis
  • uveitis.
• Pregnancy:
  • congenital varicella syndrome (≤ 20 weeks gestation)
  • severe neonatal disease (maternal rash 5 days before to 2 days after delivery).
• Immunocompromised:
  • disseminated visceral disease (high mortality without IV aciclovir).

7. Diagnosis

• Clinical: typical rash ± known exposure.
• Virology (if atypical or severe):
  • PCR of vesicle fluid; serology (IgM) for retrospective confirmation.

8. Management

8.1 Supportive Care (Immunocompetent, < 12 years, uncomplicated)

• Paracetamol for fever.
• Oral antihistamines or wet wraps for pruritus.
• Avoid NSAIDs and aspirin (risk of invasive GAS and Reye syndrome).
• Pruritus relief →
  • wet wrap dressings
  • calamine/luliconazole lotion
  • sedating antihistamine at night

8.2 Antiviral Therapy

• Oral aciclovir
  • 20 mg/kg/dose (max 800 mg) QID for 5 days if started ≤ 24 h from rash onset in high-risk but well patients (≥ 12 years unvaccinated; severe eczema; chronic lung disease; on steroids/salicylates).
• IV aciclovir
  • 10 mg/kg Q8 h (with renal monitoring) for severe disease, immunocompromise, neonates (< 7 days), or CNS involvement.

8.3 Secondary Bacterial Infection

• Empirical anti-staphylococcal therapy (e.g. flucloxacillin ± clindamycin) guided by local antimicrobial guidelines.

9. Infection Control

• Airborne + contact precautions:
  • N95/P2 mask
  • gown
  • gloves
  • eye protection.
• Single-room isolation
• clinic appointments – schedule at day’s end
• virucidal cleaning and adequate air exchange.
• Exclude non-immune staff/patients for 21 days after last exposure (28 days if VZIG received).

10. Vaccination & Post-Exposure Prophylaxis

• Routine schedule (AIR):
  • 1 dose MMRV at 18 months (funded)
  • 2nd dose ≥ 4 weeks later (ATAGI recommends a 2nd dose ≥ 4 weeks later (but not funded))
• Catch-up:
  • < 14 years: 2 total doses if not vaccinated.
  • ≥ 14 years/adults: 2 doses ≥ 4 weeks apart.
• Post-exposure:
  • live vaccine within 3–5 days (up to 7 days) for non-immune ≥ 12 months.
• Zoster immunoglobulin (ZIG):
  • within 96 h (≤ 10 days if supply delayed) for high-risk susceptibles (pregnant women, neonates of peripartum cases, immunocompromised).

11. Public Health & Reporting

• Varicella is notifiable in all Australian jurisdictions
• notify local Public Health Unit promptly.
• Exclude cases from school/childcare until all lesions crusted.
• Offer completion of 2-dose schedule to household contacts.

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Reactivation – Herpes Zoster

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1. Epidemiology & Risk Factors

• Lifetime risk ≈ 30 % (≈ 1 in 3); rises to ~50 % by 85 years.
• Major risk factors:
  • Age-related immunosenescence (usually > 50 years)
  • Immunosuppression (malignancy, HIV, transplant, corticosteroids, biologics)
  • Psychological/physical stress
  • Local trauma to a dermatome

2. Pathophysiology

• Declining VZV-specific cell-mediated immunity permits latent virus in sensory ganglia to resume lytic replication.
• Virus travels anterograde along sensory axons, causing a dermatomal vesicular eruption.
• In severe immunodeficiency, visceral dissemination can occur.

3. Clinical Features

• Prodrome (1–5 days): pain, tingling, itching, or burning in the affected dermatome; may have low-grade fever.
• Rash: unilateral, grouped vesicles on erythematous base localized to one or adjacent dermatomes (thoracic and trigeminal most common).
• Pain: often severe, can precede rash by days.

4. Complications

Complication	Key Features	At-Risk Groups
Post-herpetic neuralgia (PHN)	Persistent neuropathic pain > 90 days after rash onset; can last months to years	Older age, severe acute pain, rash extent
Ophthalmic zoster	Involvement of V1 distribution; keratitis, uveitis, optic neuritis, acute retinal necrosis	Immunocompromise, older adults
Ramsay Hunt syndrome	Geniculate ganglion involvement; vesicles in ear canal, facial palsy, hearing loss	Any age with VZV reactivation in geniculate
Neurological	Meningo-encephalitis, myelitis, cranial or peripheral motor neuropathies	Immunocompromised, older adults
VZV vasculopathy	Stroke, transient ischemic attacks	HIV, haematological malignancy
Disseminated zoster	> 20 lesions outside primary dermatome; visceral involvement (pneumonitis, hepatitis)	Severe immunosuppression
Secondary bacterial infection	Superinfection of lesions (GAS, S. aureus)	Atopic dermatitis, NSAID use, immunosuppression

5. Diagnosis

• Clinical: characteristic dermatomal distribution, acute pain.
• Laboratory (if atypical/severe): PCR of vesicular fluid or crusts; VZV IgM serology.

6. Management

6.1 Antiviral Therapy

• Initiate within 72 hours of rash onset to reduce acute pain, lesion duration, and PHN risk.
• First-line agents (oral):
  • Valaciclovir 1 g TDS for 7 days
  • Famciclovir 500 mg TDS for 7 days
  • Aciclovir 800 mg five times daily for 7–10 days
• IV aciclovir 10 mg/kg Q8 h for disseminated zoster, severe ophthalmic involvement, neurological complications, or in immunocompromised patients.

6.2 Analgesia & Symptom Control

• Acute pain:
  • Simple analgesics (paracetamol, NSAIDs unless contraindicated)
  • Opioids for severe pain
• Neuropathic pain:
  • Gabapentin or pregabalin
  • Tricyclic antidepressants (e.g., amitriptyline)
  • Topical lidocaine patches or capsaicin cream

6.3 Adjunctive Therapies

• Corticosteroids: limited evidence; may be considered in immunocompetent patients to reduce acute pain and improve quality of life, but do not prevent PHN.
• Ophthalmic involvement: urgent ophthalmology referral; combine antiviral with topical steroids/antibiotics per specialist guidance.

7. Prevention

• Herpes Zoster Vaccination (recommended by ATAGI):
  • Zostavax (live attenuated) for 50–59 years (once only)
  • Shingrix (recombinant subunit) for ≥ 50 years, two doses 2–6 months apart (preferred for immunocompetent adults)
• Post-exposure prophylaxis:
  • Varicella vaccination if no prior immunity and exposure to disseminated zoster

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Clinical Tip: Early recognition and prompt antiviral therapy are key to reducing acute morbidity and the risk/severity of post-herpetic neuralgia. Ensure high-risk patients (elderly, immunosuppressed) are vaccinated according to current recommendations.

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Vaccine “Breakthrough” Infections

No vaccine is 100 % effective. A small proportion of fully vaccinated individuals can still develop disease if exposed—so-called “breakthrough” infections.

1. Varicella (Chickenpox)

• One-dose effectiveness:
  • ~ 80–85 % against any varicella
  • ~ 95–98 % against severe disease (> 500 lesions)
• Breakthrough varicella: Occurs in ≈ 15–20 % after a single dose.
  • Clinical pattern: Usually mild (most have < 50 lesions, low or no fever).
  • Contagiousness: Still transmissible to others.
• Two-dose schedule: Significantly reduces breakthrough risk; recommended at ≥ 4 weeks after first dose for children < 14 years
  • While ATAGI advises two doses for optimal protection, the government currently funds one dose at 18 months based on cost-effectiveness and programmatic considerations
    • MMRV – Priorix Tetra – $80
    • MMR – Priorix – $30

Implication: A vaccinated child can still develop chickenpox if exposed, but the illness is typically milder and less likely to require hospitalisation.

2. Measles

• One-dose effectiveness: ≈ 96 % in Australia
• Two-dose effectiveness: ≈ 99 % in Australia; one Cochrane review reports 95 % for a single dose and near-complete protection after two doses
• Breakthrough measles: Very rare after two doses; most “cases” in vaccinated individuals occur with only one dose or waning immunity in adults.

Implication: Two doses confer near-complete protection; measles in a fully two-dose vaccinated person is extremely uncommon.

3. Mumps

• One-dose effectiveness: 60–90 % (varies by strain; Jeryl Lynn strain ≈ 69–81 %)
• Two-dose effectiveness: Up to ~ 95–100 % in immunogenicity studies; real-world effectiveness ≈ 86 % (range 32–95 %)
• Breakthrough mumps: More common than measles or rubella; outbreaks in highly vaccinated populations have occurred, particularly among young adults.

Implication: Even with two doses, a small percentage remain susceptible; mumps can still spread in close-contact settings, though disease tends to be milder in vaccinated individuals.

4. Rubella

• One-dose effectiveness: ≈ 94.5–97 % against clinical rubella
• Two-dose schedule: Ensures herd immunity and prevents congenital rubella; breakthrough rubella is very rare.
• Breakthrough rubella: Uncommon in well-vaccinated populations; most vaccinated non-immune individuals are identified via serology before pregnancy.

Implication: Single-dose rubella vaccination protects the vast majority; two doses are recommended for women of childbearing age to maximise protection.

Key Take-Home Points

1. Breakthrough disease is usually milder than in unvaccinated individuals.
2. Two-dose schedules (for varicella and MMR) significantly enhance protection and are routinely recommended.
3. Ongoing surveillance and high coverage (≥ 95 %) are critical to minimise circulation and protect vulnerable groups (e.g., infants too young to be vaccinated, immunocompromised people, and pregnant women).