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Infectious Diseases

Chickenpox

A highly contagious viral infection caused by the Varicella-Zoster Virus (VZV), characterized by a generalized, itchy, vesicular rash. Usually a mild childhood illness, but can be severe in adults, newborns, and immunocompromised individuals.

Also known as: Varicella

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Referral and warning signs

When to refer

Refer to Hospital (HC4/H) if: Signs of complications (pneumonia - cough/dyspnea, encephalitis - altered consciousness/seizures), Severe disease, High-risk patient (immunocompromised, pregnant, neonate), Significant secondary bacterial infection.

Red flags

  • Difficulty breathing / Cough / Chest pain.
  • Altered mental status / Stiff neck / Seizures.
  • High fever persisting beyond 4 days.
  • Extensive hemorrhagic lesions.
  • Signs of severe secondary bacterial infection (spreading redness/pain).
  • Lesions in the eye.
  • Neonate with varicella.
  • Pregnant woman with varicella.

Signs and symptoms

  • Incubation period: 10-21 days (average 14-16 days).
  • Prodrome (1-2 days before rash, esp. in older children/adults): Mild fever, malaise, headache.
  • Rash: Evolves rapidly through stages:
  • - Macules (red spots) -> Papules (raised bumps) -> Vesicles ('dew drops on a rose petal' - small fluid-filled blisters on red base) -> Pustules -> Crusting/Scabbing.
  • - Intense itching (pruritus).
  • - Rash typically starts on trunk/scalp/face, then spreads centrifugally to limbs.
  • - Lesions appear in successive 'crops' over several days, so different stages (macules, papules, vesicles, crusts) are present simultaneously ('polymorphic rash').
  • - Lesions may occur on mucous membranes (mouth, conjunctiva, vagina).
  • Low-grade fever usually present during rash.
  • Patient contagious from 1-2 days before rash onset until all lesions have crusted over (usually ~5-7 days after rash onset).

Risk factors

  • No prior infection or vaccination.
  • Exposure to infected individual (highly contagious via respiratory droplets and direct contact with vesicle fluid).
  • Immunocompromised state (higher risk of severe/complicated disease).
  • Pregnancy (risk to mother and fetus/neonate).
  • Adult age (tend to have more severe disease).

Diagnosis

Clinical assessment

Diagnosis usually based on characteristic clinical presentation: history of exposure (if known) and typical polymorphic, itchy, vesicular rash starting centrally.

Differential diagnosis

  • Insect bites (often grouped, lack evolution through stages).
  • Scabies (burrows, intense itching worse at night, different distribution).
  • Impetigo (honey-coloured crusts).
  • Drug eruptions.
  • Hand, Foot, and Mouth Disease (vesicles mainly on hands/feet/mouth).
  • Disseminated Herpes Simplex (in immunocompromised).
  • Smallpox (eradicated - lesions all at same stage, centrifugal distribution).
  • Monkeypox (lesions often larger, umbilicated, prominent lymphadenopathy).

Investigations

  • Usually clinical diagnosis.
  • Viral PCR or Direct Fluorescent Antibody (DFA) test on vesicle fluid/scraping (confirmatory, rarely needed for typical cases).
  • Serology (VZV IgM/IgG) - useful for confirming immunity or recent infection.

Diagnostic criteria

Clinical diagnosis based on characteristic rash.

Management

Non-pharmacological management

  • Symptomatic Relief:
  • - Keep skin clean and cool.
  • - Tepid baths (may add oatmeal colloid).
  • - Calamine lotion or other anti-itch preparations applied topically. (LOC: HC2)
  • - Keep fingernails short to minimize scratching/secondary infection.
  • Isolation: Keep child home from school/daycare until all lesions crusted to prevent spread.

Pharmacological treatment

  • Antipyretics: Paracetamol for fever. Avoid Aspirin in children/adolescents due to risk of Reye's syndrome.
  • Antihistamines: Oral antihistamines (e.g., Chlorphenamine 1-2mg Q12H <5y; 4mg Q12H >5y/Adult) for itching. (LOC: HC2)
  • Antiviral Therapy (Acyclovir): Consider ONLY for high-risk individuals or severe disease (start within 24-72h of rash onset for best effect). Not routinely recommended for healthy children.
  • - Indications: Adults/Adolescents (>12y), Secondary household cases (often more severe), Chronic skin/lung disease, Patients on long-term salicylates or short-course/inhaled steroids, Immunocompromised, Neonates, Pregnant women (specialist consultation).
  • - Dose (UCG for >12y/Adults): Acyclovir 800mg PO 5 times daily for 7 days. (LOC: HC4)
  • - IV Acyclovir needed for severe complications (pneumonia, encephalitis) or severe immunocompromise.
  • Antibiotics: ONLY if secondary bacterial infection of skin lesions develops (e.g., impetigo - treat with topical/oral anti-staphylococcal antibiotics like Cloxacillin/Flucloxacillin).

Monitoring

Monitor for signs of complications.

Complications

  • Secondary bacterial skin infection (Staph aureus, Strep pyogenes) -> Impetigo, Cellulitis, Abscess, Necrotizing fasciitis (rare).
  • Varicella Pneumonia (more common/severe in adults, smokers, pregnant women, immunocompromised).
  • Neurological complications: Cerebellar ataxia (most common neuro complication in children, usually benign), Encephalitis, Meningitis, Transverse myelitis, Guillain-Barré syndrome.
  • Hepatitis.
  • Thrombocytopenia / Purpura fulminans.
  • Reye's syndrome (if aspirin used).
  • Severe/disseminated disease in immunocompromised.
  • Congenital Varicella Syndrome (if infection in early pregnancy).
  • Neonatal Varicella (if maternal infection near delivery).

Prevention

  • Vaccination: Varicella vaccine (live attenuated) provides effective protection. Included in some national programs, available privately.
  • Post-Exposure Prophylaxis (PEP):
  • - Varicella Vaccine: Can prevent or modify illness if given within 3-5 days of exposure to susceptible individuals.
  • - Varicella-Zoster Immunoglobulin (VZIG): For high-risk susceptible individuals exposed (immunocompromised, pregnant women, neonates). Given within 96h ideally (up to 10 days). Specialist use.
  • Isolation of infected individuals.

Patient education

  • Explanation of chickenpox as a contagious viral illness.
  • Expected course (rash evolution, crusting).
  • Symptomatic relief (calamine, cool baths, antihistamines).
  • Importance of avoiding scratching.
  • Isolation measures to prevent spread.
  • When to seek medical review (signs of complications).
  • Avoidance of aspirin.

Uganda-specific notes

Common childhood illness. Vaccination not part of routine EPI but available privately. Management mainly symptomatic. Acyclovir use limited to high-risk/severe cases due to cost/availability. Secondary bacterial skin infections common.

References

  • Uganda Clinical Guidelines (UCG) 2023

    Chapter 2, Section 2.3.2

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