Conditions · Pediatrics and neonatology
Varicella (chickenpox) !
Chickenpox is a very contagious virus infection with itchy blisters in different stages. Usually mild in children; can be severe in others.
Updated 2026-11-01
Structures involved
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Microorganisms that cause it
In embryology
In the clinical exam
Why it happens
What it is
The primary infection by varicella-zoster virus (VZV), a herpesvirus, causing fever and an itchy vesicular rash with lesions in different stages. The virus then stays dormant in sensory ganglia and can reactivate later as herpes zoster.
Who gets it
Very common in childhood where vaccination is not universal. Colombia added varicella vaccine to its national schedule in 2015, which has reduced cases and outbreaks, although outbreaks still occur in schools, prisons and military settings. Severe disease is more frequent in adolescents, adults, pregnant women and immunosuppressed people.
Causes
- Varicella-zoster virus (human herpesvirus 3)
- Spread by respiratory droplets, aerosols and direct contact with blister fluid, including from herpes zoster lesions
- Contagious from 1 to 2 days before the rash until all lesions have crusted
Risk factors
- No previous infection or vaccination
- Close household or school contact with a case
- Severe disease: age over 12 years, pregnancy, newborns of mothers with peripartum varicella
- Immunosuppression (leukaemia, transplant, high-dose corticosteroids, HIV)
- Chronic skin or lung disease
Pathophysiology
VZV enters through the respiratory mucosa, replicates in regional lymph nodes and spreads through the blood in two waves to the skin, where it forms intraepidermal vesicles. Successive waves of viraemia explain why papules, vesicles and crusts coexist. The virus travels along sensory nerves to the dorsal root and cranial nerve ganglia, where it stays latent for life.
Symptoms and signs
- Incubation of about 10 to 21 days
- Mild fever, malaise and poor appetite, often a day before the rash
- Intensely itchy rash that starts on the scalp, face and trunk and spreads to the limbs
- Lesions evolve from red macules to papules to clear vesicles ('dewdrop on a rose petal') to crusts
- Lesions in different stages at the same time in one area (polymorphism)
- Vesicles or ulcers on mucosa (mouth, conjunctiva, genitals)
Diagnosis
- Clinical
- Usually clinical: the typical itchy vesicular rash with lesions in different stages, starting centrally, in a non-immune person with recent exposure.
- Tests
- PCR for VZV DNA from vesicle fluid or a scraped lesion when the picture is atypical, the patient is high risk or in an outbreak; serology (IgG) to check immunity in pregnant women or exposed high-risk people.
- Imaging
- Chest X-ray if pneumonia is suspected (diffuse nodular infiltrates); brain imaging for neurological complications.
Differential diagnosis
- Disseminated herpes simplex or herpes zoster
- Hand, foot and mouth disease and other enteroviral rashes
- Impetigo (bullous)
- Insect bites and papular urticaria
- Monkeypox (mpox)
- Drug eruption
Goal of treatment
Relieve itch and fever, prevent scratching and bacterial superinfection, give antivirals to people at risk of severe disease, and prevent spread to susceptible high-risk contacts.
Treatment
- Conservative
- Symptomatic care: short nails, cool baths, calamine-type lotions and oral antihistamines for itch, fluids, and paracetamol for fever; aspirin is avoided in children because of Reye syndrome.
- Medical
- Oral acyclovir or valacyclovir, best within 24 hours of the rash, for adolescents, adults, secondary household cases and children with chronic skin or lung disease or on corticosteroids; not routine in healthy young children.
- Medical
- Intravenous acyclovir for immunosuppressed patients, varicella pneumonia, encephalitis and severe disease in pregnancy; antibiotics for bacterial skin infection.
- Follow-up
- Infection control and nursing: airborne and contact isolation until all lesions crust, exclusion from school or daycare, varicella vaccine within 3 to 5 days or varicella-zoster immunoglobulin for exposed susceptible high-risk people, monitoring of breathing, skin and neurological status.
Drugs for this condition
Complications
- Bacterial skin and soft-tissue infection (Streptococcus pyogenes, Staphylococcus aureus), including necrotising fasciitis
- Varicella pneumonia
- Acute cerebellar ataxia and encephalitis
- Reye syndrome when aspirin is given
- Congenital varicella syndrome (early pregnancy) and severe neonatal varicella
- Later reactivation as herpes zoster
Prognosis
In healthy children it is usually mild and resolves in about a week with lifelong immunity. Morbidity and mortality are much higher in adults, pregnant women, newborns and immunosuppressed patients.
Prevention
- Two doses of varicella vaccine (live attenuated)
- Post-exposure vaccination or immunoglobulin for susceptible contacts
- Isolation of cases until lesions crust
- Checking immunity before pregnancy and before immunosuppression
Test yourself
Think of the answer, then tap the question to see it.
What is the hallmark of the varicella rash?
Itchy vesicles on a red base appearing in crops, with macules, papules, vesicles and crusts present at the same time.
Until when is a child with chickenpox contagious?
From 1 to 2 days before the rash until all lesions have crusted.
Why is aspirin avoided in children with varicella?
Because of the risk of Reye syndrome (acute liver failure with encephalopathy).
Which is the most common complication of varicella in children?
Bacterial superinfection of the skin lesions, mainly by Streptococcus pyogenes or Staphylococcus aureus.
Where does varicella-zoster virus stay latent after the primary infection?
In sensory ganglia (dorsal root and cranial nerve ganglia), from which it can reactivate as herpes zoster.
Related conditions
- Herpes zoster (shingles)
- Measles
- Cellulitis of the leg
- Community-acquired pneumonia
- Febrile seizures
- HIV infection and AIDS
Educational information, not medical advice. For any symptom, see a health professional.
Sources: About Chickenpox | Chickenpox (Varicella) | CDC (Centers for Disease Control and Prevention, 2024); Chickenpox: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2024).
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Representative model, for educational purposes only.
