Varicella-Zoster Virus Infection in Children
Introduction to Varicella-Zoster Virus Infection in Children
Varicella-Zoster Virus (VZV) infection, commonly known as chickenpox, is a highly contagious disease primarily affecting children. It is caused by the varicella-zoster virus, a member of the herpesvirus family. The infection typically results in a characteristic itchy, vesicular rash and is usually self-limiting in immunocompetent children. However, it can lead to serious complications, especially in immunocompromised individuals, neonates, and adults.
Key points:
- Chickenpox is the primary infection caused by VZV.
- After primary infection, the virus remains dormant in sensory nerve ganglia.
- Reactivation of the virus later in life causes herpes zoster (shingles).
- Vaccination has significantly reduced the incidence of chickenpox in many countries.
Etiology of Varicella-Zoster Virus Infection
Varicella-Zoster Virus (VZV) is the causative agent of chickenpox. It belongs to the Alphaherpesvirinae subfamily of herpesviruses.
Characteristics of VZV:
- Enveloped DNA virus
- Icosahedral capsid
- Approximately 125 nm in diameter
- Contains double-stranded DNA genome
Transmission:
- Highly contagious
- Spread through respiratory droplets or direct contact with vesicular fluid
- Airborne transmission possible
- Incubation period: 10-21 days (average 14 days)
Epidemiology of Varicella-Zoster Virus Infection in Children
Chickenpox is a common childhood illness, but its epidemiology has changed significantly since the introduction of the varicella vaccine.
Key epidemiological features:
- Peak incidence: 5-9 years of age in unvaccinated populations
- Seasonal variation: More common in late winter and early spring in temperate climates
- Global distribution: Endemic worldwide
- Vaccination impact: >90% reduction in incidence in countries with universal vaccination programs
Risk factors for severe disease:
- Age: Neonates and adults are at higher risk for complications
- Immunocompromised status
- Pregnancy: Risk of congenital varicella syndrome
- Chronic skin or lung disease
Pathophysiology of Varicella-Zoster Virus Infection
The pathophysiology of VZV infection involves several stages:
- Initial replication: Occurs in the nasopharynx and regional lymph nodes
- Primary viremia: Virus spreads to reticuloendothelial system
- Secondary viremia: Widespread dissemination to skin and visceral organs
- Skin lesion formation: Virus infects epidermal cells, causing characteristic vesicles
- Latency establishment: VZV remains dormant in sensory nerve ganglia
Immune response:
- Innate immunity: Interferon production limits viral spread
- Humoral immunity: Antibodies help clear the virus and provide long-term immunity
- Cell-mediated immunity: Critical for controlling viral replication and preventing reactivation
Clinical Presentation of Varicella-Zoster Virus Infection in Children
The clinical presentation of chickenpox typically follows a characteristic pattern:
- Prodromal phase (1-2 days):
- Low-grade fever
- Malaise
- Anorexia
- Exanthem phase:
- Pruritic, vesicular rash
- Begins on trunk, face, and scalp, then spreads to extremities
- Lesions progress: Macules → papules → vesicles → pustules → crusts
- New lesions appear in crops over 3-5 days
- Crusting phase:
- Lesions crust over and heal within 1-2 weeks
- Patients are contagious until all lesions have crusted
Associated symptoms:
- Fever (usually <39°C)
- Pruritus
- Fatigue
- Headache
- Abdominal pain (in some cases)
Diagnosis of Varicella-Zoster Virus Infection
Diagnosis of chickenpox is typically based on clinical presentation. However, laboratory confirmation may be necessary in certain cases.
Clinical diagnosis:
- Characteristic rash appearance and distribution
- History of exposure to VZV
- Typical clinical course
Laboratory diagnosis:
- Polymerase Chain Reaction (PCR):
- Most sensitive and specific method
- Can detect VZV DNA in vesicular fluid, scabs, or blood
- Direct Fluorescent Antibody (DFA) testing:
- Rapid test using vesicular fluid
- Less sensitive than PCR
- Serology:
- IgM and IgG antibody detection
- Useful for determining immune status or confirming recent infection
- Viral culture:
- Less commonly used due to slow turnaround time
- Can differentiate between wild-type and vaccine strain VZV
Treatment of Varicella-Zoster Virus Infection in Children
Treatment for chickenpox in children is primarily supportive, but antiviral therapy may be indicated in certain cases.
Supportive care:
- Antipyretics (acetaminophen) for fever
- Antihistamines or topical treatments (e.g., calamine lotion) for pruritus
- Proper skin hygiene to prevent secondary bacterial infections
- Adequate hydration and nutrition
Antiviral therapy:
- Acyclovir, valacyclovir, or famciclovir
- Indications for antiviral treatment in children:
- Immunocompromised patients
- Chronic skin or pulmonary disorders
- Prolonged or severe disease
- Neonates
- Dosage and duration depend on patient characteristics and severity of infection
Management of complications:
- Antibiotics for secondary bacterial infections
- Hospitalization and supportive care for severe complications (e.g., pneumonia, encephalitis)
Complications of Varicella-Zoster Virus Infection
While chickenpox is usually self-limiting in healthy children, complications can occur, especially in high-risk groups.
Common complications:
- Secondary bacterial skin infections (e.g., impetigo, cellulitis)
- Scarring
- Pneumonia (more common in adults and immunocompromised patients)
- Dehydration
Severe complications:
- Neurological:
- Cerebellar ataxia
- Encephalitis
- Aseptic meningitis
- Guillain-Barré syndrome
- Hematological:
- Thrombocytopenia
- Purpura fulminans
- Others:
- Myocarditis
- Hepatitis
- Glomerulonephritis
Special considerations:
- Congenital varicella syndrome: Can occur if mother is infected during first 20 weeks of pregnancy
- Neonatal varicella: Severe infection in newborns whose mothers develop chickenpox around the time of delivery
Prevention of Varicella-Zoster Virus Infection
Prevention of chickenpox primarily relies on vaccination and appropriate management of exposed individuals.
Vaccination:
- Live attenuated varicella vaccine
- Recommended schedule:
- First dose: 12-15 months of age
- Second dose: 4-6 years of age
- Efficacy: >90% protection against severe disease, 70-90% against any varicella infection
- Contraindications: Immunocompromised state, pregnancy, severe illness
Post-exposure prophylaxis:
- Vaccination: Can prevent or attenuate disease if given within 3-5 days of exposure
- Varicella-Zoster Immune Globulin (VZIG):
- For high-risk individuals who cannot receive the vaccine
- Must be administered within 10 days of exposure
Infection control measures:
- Isolation of infected individuals until lesions have crusted
- Proper hand hygiene
- Avoiding sharing personal items with infected individuals
Varicella-Zoster Virus Infection in Children
- What is the causative agent of chickenpox and shingles?
Varicella-zoster virus (VZV) - Which family of viruses does VZV belong to?
Herpesviridae - What is the primary mode of transmission for varicella (chickenpox)?
Respiratory droplets and direct contact with lesions - What is the typical incubation period for varicella?
14-16 days (range: 10-21 days) - Which of the following best describes the characteristic rash of varicella?
Pruritic, maculopapular rash progressing to vesicles, pustules, and crusts - What is the term for the reactivation of latent VZV infection?
Herpes zoster (shingles) - In which nerve tissue does VZV establish latency?
Dorsal root ganglia and cranial nerve ganglia - What is the recommended isolation period for children with varicella?
Until all lesions have crusted (usually 5-7 days) - Which of the following is NOT a typical complication of varicella in children?
Guillain-Barré syndrome - What is the most common bacterial superinfection in children with varicella?
Group A Streptococcus skin infection - Which age group is at highest risk for severe varicella complications?
Infants and adolescents - What is the name of the severe complication of varicella characterized by hemorrhagic vesicles and purpura?
Varicella gangrenosa - Which antiviral medication is recommended for treatment of varicella in high-risk children?
Acyclovir - What is the recommended number of doses in the primary varicella vaccination series?
Two doses - At what age is the first dose of varicella vaccine typically administered?
12-15 months - What is the minimum interval between the two doses of varicella vaccine?
3 months (for children aged 12 months to 12 years) - Which of the following is a contraindication for varicella vaccination?
Pregnancy - What is the effectiveness of two doses of varicella vaccine in preventing all varicella infections?
Approximately 90% - What is the term for varicella infection occurring in a vaccinated individual?
Breakthrough varicella - Which of the following is NOT a typical feature of breakthrough varicella?
High fever lasting more than 5 days - What is the recommended post-exposure prophylaxis for susceptible immunocompetent children exposed to varicella?
Varicella vaccination within 3-5 days of exposure - What is the recommended post-exposure prophylaxis for susceptible immunocompromised children exposed to varicella?
Varicella-zoster immunoglobulin (VZIG) - Which of the following maternal infections during pregnancy can result in congenital varicella syndrome?
Varicella infection in the first 20 weeks of gestation - What is the typical clinical presentation of herpes zoster in children?
Painful, unilateral vesicular rash in a dermatomal distribution - Which cranial nerve is most commonly affected in herpes zoster ophthalmicus?
Trigeminal nerve (ophthalmic division) - What is the term for persistent pain lasting more than 90 days after the onset of herpes zoster?
Post-herpetic neuralgia - Which of the following is NOT a typical CSF finding in varicella meningitis?
Predominantly neutrophilic pleocytosis - What is the name of the neurological complication that can occur weeks after varicella infection?
Acute cerebellar ataxia - Which of the following best describes the relationship between varicella and herpes zoster?
Herpes zoster occurs due to reactivation of latent VZV from primary varicella infection - What is the estimated risk of developing herpes zoster in individuals with a history of varicella infection?
25-30% lifetime risk - Which of the following factors increases the risk of herpes zoster in children?
Intrauterine or infantile varicella infection
