Overview -
Chickenpox (varicella) is a highly contagious viral illness caused by the
varicella-zoster virus (VZV), a member of the herpesvirus family. It most
commonly affects children but can occur at any age. Following initial
infection, VZV establishes latency in sensory nerve ganglia and can reactivate
years later as herpes zoster (shingles).
1. Causes
- Pathogen:
- Varicella-zoster virus
(VZV), an enveloped DNA virus in the Herpesviridae family.
- VZV has two clinical
manifestations:
- Primary infection → Chickenpox (varicella)
- Reactivation → Shingles (herpes
zoster)
- Transmission Routes:
- Respiratory Droplets and
Aerosols:
Infectious droplets expelled when an infected person coughs or sneezes.
- Direct Contact with Lesions: Fluid from vesicles
contains high viral titers; touching or scratching active lesions can
transmit VZV.
- Airborne Spread: Virus can remain
suspended in air for a short period, allowing spread beyond close
contacts.
- Risk Factors:
- Lack of Immunity: Unvaccinated children and
adults are at highest risk.
- Household Exposure: Living with someone who
has active chickenpox or shingles.
- Immunocompromise: Patients with weakened
immune systems (e.g., on chemotherapy, HIV infection) are more
susceptible to severe disease.
- Pregnancy: Pregnant women exposed
during the first or second trimester risk congenital varicella syndrome
in the fetus.
- Conditions That Promote
Outbreaks:
- Low vaccination coverage in
a community.
- Crowded settings (daycares,
schools, military barracks).
- Outbreaks often occur in
late winter to early spring in temperate climates.
2. Symptoms
Chickenpox
generally follows a predictable timeline once exposed.
- Incubation Period
- Typically 10–21 days
(average ~14 days) after exposure to an infectious individual.
- Patients are contagious
from about 1–2 days before rash onset until all lesions have
crusted (usually ~5–7 days after rash begins).
- Prodromal Phase (Pre-rash)
- Mild fever (≤38.9 °C / 102
°F)
- Malaise, headache, and
anorexia may occur.
- In children, prodrome is
often minimal or absent; adults may have more pronounced flu-like
symptoms.
- Rash (Exanthem) Phase
- Onset: Sudden appearance of
pruritic (itchy), red macules that rapidly progress to papules, then
vesicles (“dew-drop on a rose petal”), and finally crust over.
- Distribution:
- Begins on the trunk,
then spreads to the face, scalp, and extremities.
- Lesions appear in
successive “crops” over 3–5 days, so one can see macules,
papules, vesicles, and crusts simultaneously.
- Number of Lesions:
- Varies from ≤50 lesions
in mild cases to thousands in more severe cases.
- Associated Symptoms:
- Pruritus (often intense),
which can lead to excoriation and secondary bacterial infection if
scratched.
- Low-grade fever may
persist for the first 2–3 days of rash.
- Recovery Phase
- Lesions crust over within 4–7
days of appearance.
- New crops of lesions
typically stop by day 5, and all lesions generally crust by day 10–14.
- Crusts fall off
spontaneously without scarring in most cases, though deeper or
secondarily infected lesions can leave pitted scars.
- Severity Spectrum
- Mild:
- Fewer than 50 lesions.
Minimal fever. Rapid recovery in otherwise healthy children.
- Moderate:
- Several hundred lesions.
More pronounced fever (38.9 °C to 39.4 °C / 102 °F to 103 °F). Moderate
itching.
- Severe:
- >500 lesions or widespread involvement
in immunocompromised or adult patients.
- High fever (>39.5 °C /
103 °F), persistent vomiting, dehydration risk.
- Complications more likely
(see below).
- Complications (Especially in
High-Risk Groups)
- Bacterial Superinfection: Staphylococcus aureus
or Streptococcus pyogenes invasion of excoriated skin lesions
leading to impetigo, cellulitis, or even necrotizing fasciitis.
- Pneumonia: More common in
adolescents, adults, pregnant women, and immunocompromised. Can progress
to respiratory failure.
- CNS Involvement:
- Acute Cerebellar Ataxia: Most common neurologic
complication in children; manifests ~1 week post-rash with unsteady
gait.
- Encephalitis: Rare but serious, with
altered mental status, seizures, and potential for long-term sequelae.
- Hepatitis: Elevated liver enzymes,
especially in adults and immunosuppressed.
- Thrombocytopenia: Transient drop in
platelets.
- Reye Syndrome: Very rare; classically
associated with aspirin use in children with varicella.
- Congenital Varicella
Syndrome:
If maternal infection occurs between weeks 8 and 20 of gestation,
fetus may develop limb hypoplasia, skin scarring, ocular abnormalities,
neurologic defects.
- Neonatal Varicella: If maternal infection
occurs from 5 days before to 2 days after delivery, the newborn is
at high risk of severe, disseminated disease with ~30% mortality without
treatment.
3. Treatment
Most
healthy children require only supportive care. Antiviral therapy and additional
interventions are reserved for high-risk groups or complicated cases.
- Supportive Care (for
Uncomplicated Cases in Otherwise Healthy Children)
- Pruritus Control:
- Oral antihistamines (e.g., chlorpheniramine
or cetirizine) to reduce itching.
- Topical lotions (e.g., calamine lotion,
colloidal oatmeal baths) can soothe skin.
- Fever and Pain Management:
- Acetaminophen
(paracetamol)
for fever and discomfort.
- Avoid aspirin due to Reye syndrome
risk.
- Hydration and Nutrition:
- Encourage fluids to
prevent dehydration from fever or reduced intake.
- Offer soft, bland foods if
mouth lesions are painful.
- Antiviral Therapy
- Indications:
- Immunocompromised patients (e.g., those on
chemotherapy, transplant recipients, HIV with low CD4).
- Adolescents and adults (≥13 years) even if
healthy, since morbidity is higher.
- Pregnant women (especially in second
half of pregnancy) to reduce severity and risk to fetus/newborn.
- Neonates exposed perinatally.
- Patients with chronic skin
or lung disease (e.g., eczema, asthma) at higher risk for
complications.
- First-line Agent:
- Oral Acyclovir: 20 mg/kg per dose
(maximum 800 mg) four times daily for 5–7 days in children; in adults,
800 mg five times daily for 7 days (ideally within 24 hours of rash
onset).
- Alternative Agents (where acyclovir
resistance or contraindications):
- Valacyclovir (more bioavailable
prodrug of acyclovir)
- Famciclovir (prodrug of penciclovir)
- Intravenous Acyclovir: 10 mg/kg IV every 8
hours for severe disseminated disease or VZV pneumonia, typically for
7–10 days, especially in immunocompromised or neonatal varicella.
- Additional Interventions
- IVIG (Varicella Zoster
Immune Globulin):
- For certain high-risk
exposures (e.g., pregnant women, immunocompromised contacts) to
attenuate disease.
- Ideally administered
within 96 hours of exposure.
- Hospitalization Criteria:
- Severe dehydration,
inability to maintain oral intake.
- Signs of pneumonia or
respiratory compromise.
- Neurologic complications
(e.g., encephalitis).
- Neonates with early (<5
days before birth or ≤48 hours after birth) maternal varicella exposure.
4. Prevention
Effective
prevention hinges on vaccination, isolation of cases, and general
infection-control measures.
- Vaccination
- Live Attenuated Varicella
Vaccine
(Oka strain)
- Schedule (per most national
guidelines):
- Dose 1: 12–15 months of age
(first birthday).
- Dose 2: 4–6 years of age (prior
to school entry).
- Catch-Up: Unvaccinated children
≥7 years receive two doses separated by 3–8 weeks.
- Adolescents & Adults: Two doses separated by
4–8 weeks if no history of varicella or seronegative status confirmed.
- Efficacy:
- ≈85–90% protection
against any varicella; >95% protection against severe disease.
- Vaccine-associated rash
can occur in ~5%–10% of vaccinees, typically mild and fewer than 50
lesions.
- Contraindications:
- Severe immunodeficiency
(e.g., advanced HIV with CD4 <200 cells/mm³, leukemia).
- Pregnancy (live vaccine
risk); women should avoid pregnancy for 1 month after vaccination.
- History of anaphylactic
reaction to vaccine components (e.g., neomycin).
- Post-Exposure Prophylaxis
- Vaccination within 3–5 days of exposure can attenuate
or prevent disease in susceptible healthy individuals.
- VariZIG (Varicella Zoster
Immune Globulin):
- For high-risk groups who
cannot receive vaccine or after vaccine failure:
- Immunocompromised
patients, neonates born to mothers with peripartum varicella, pregnant
women without evidence of immunity.
- Administer within 96
hours (ideally within 72 hours) of exposure.
- Infection Control and
Isolation
- Case Isolation:
- Infected individuals
should stay home until all lesions have crusted (approximately 5–7 days
after rash onset).
- Hospital Precautions:
- Airborne and contact
precautions (negative-pressure room and use of gloves/gown).
- Household Precautions:
- Cohorting of cases, strict
hand hygiene, and covering of lesions to reduce spread.
- Public Health Strategies
- High Vaccination Coverage: Achieving and sustaining
≥90% coverage decreases circulation of wild-type VZV.
- Outbreak Control:
- Identification of
susceptible individuals (serological testing or vaccine history review).
- Immediate administration
of post-exposure vaccine or VariZIG when indicated.
- Awareness Campaigns: Education about the
importance of vaccinating before childbearing age and the availability of
varicella vaccination for adults.
5. Special Populations
- Pregnant Women
- Risks:
- Maternal varicella pneumonia
(higher morbidity/mortality).
- Congenital varicella
syndrome (rare but serious).
- Neonatal varicella if
maternal infection occurs near delivery.
- Management:
- Susceptible Pregnant
Contacts:
Administer VariZIG within 96 hours of exposure.
- Active Infection: Hospitalize for IV
acyclovir; fetal monitoring; consider obstetric consultation.
- Neonates
- High-Risk Window:
- If mother develops
varicella 5 days before to 2 days after delivery.
- Management:
- Administer IVIG (VariZIG)
to neonate immediately.
- Initiate IV acyclovir at
first sign of rash or confirmed infection.
- Immunocompromised Patients
- Prophylaxis:
- Consider Varicella Zoster
Immune Globulin after exposure.
- Treatment:
- Early initiation of IV
acyclovir for any signs of varicella.
- Hospitalize for close
monitoring (risk of disseminated disease).
- Adults (Especially ≥20 Years
Old)
- More likely to experience
severe disease (e.g., pneumonia, encephalitis).
- Vaccination recommended if
no prior history or serologic evidence of immunity.
6. Epidemiology
- Global Burden:
- Before widespread
vaccination, nearly all individuals contracted varicella during
childhood.
- With routine childhood
immunization (introduced in many countries in the late 1990s), incidence has
declined dramatically.
- Current Patterns (as of 2025):
- In countries with high
vaccine coverage (>90%), varicella is now uncommon; most cases
represent breakthrough infections in vaccinated persons (which tend to be
milder).
- In regions without
universal varicella vaccination, seasonal peaks still occur in late
winter to early spring.
- Outbreaks:
- Sometimes occur in schools
or daycare centers when pockets of unvaccinated individuals exist.
- Adult outbreaks can occur
in workplace or military settings if vaccination gaps exist.
7. Key Takeaways
- Etiology: Caused by varicella-zoster
virus; spreads via respiratory droplets and direct contact with vesicle
fluid.
- Clinical Features: Fever and crops of
pruritic vesicular rash; contagious from 1–2 days before rash until all
lesions crust.
- Treatment: Supportive care for most
healthy children; antivirals (acyclovir, valacyclovir) recommended for
high-risk groups, adults, and complicated cases.
- Prevention:
- Two-dose varicella vaccine
series is highly effective; consider catch-up vaccination in unimmunized
adolescents and adults.
- Post-exposure prophylaxis
(vaccine or VariZIG) reduces severity in susceptible high-risk contacts.
- Strict isolation of active
cases until all lesions crust.
- Complications: Bacterial superinfection
of lesions, pneumonia, neurologic involvement, congenital infection, and
severe neonatal disease when maternal infection is peripartum.
