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Infectious Disease and Microbiology – Chickenpox (Varicella)
Chickenpox is a highly contagious febrile illness of childhood caused by primary infection with the varicella zoster virus (VZV). It is characterized by a generalized pruritic rash in which lesions at different stages of development—macules, papules, vesicles, pustules, and crusts—are present simultaneously.
The disease occurs worldwide and shows seasonal peaks in late winter and early spring. Before widespread vaccination, the primary attack rate in susceptible individuals was approximately 90%, with household secondary attack rates of 70–90%. Since implementation of routine vaccination programs, incidence, hospitalizations, complications, and deaths have declined dramatically. Both sexes are equally affected. Most cases occur in young children, although an increasing proportion of cases now occur in adolescents and adults in partially vaccinated populations.
Risk factors include close contact with an infected individual (varicella or herpes zoster), lack of immunity, and increasing age at exposure. Approximately 90% of individuals aged 15 years or older are immune, but 10% remain susceptible. Adults, pregnant women, and immunocompromised individuals are at higher risk for severe disease and complications.
Varicella zoster virus is a DNA virus (human herpesvirus 3) in the Herpesviridae family. Humans are the only known reservoir. Transmission occurs via respiratory droplets or direct contact with vesicular fluid. The virus enters through the respiratory mucosa, replicates in regional lymph nodes, and spreads through primary viremia. A secondary viremia disseminates the virus to the skin and other organs. After primary infection, the virus remains latent in sensory ganglia and may reactivate later in life as herpes zoster.
The incubation period is typically 10–14 days (range 10–21 days). Patients are infectious from approximately 48 hours before rash onset until all lesions have crusted. In immunocompetent children, mild prodromal symptoms such as malaise and low-grade fever may precede the rash by 1–2 days. The rash begins on the face and trunk and spreads centrifugally, sometimes involving mucous membranes. Lesions evolve rapidly from macules to papules and then to clear vesicles on an erythematous base. Vesicular fluid becomes turbid, crusting follows, and new crops of lesions appear over 2–4 days. Crusts fall off within 1–2 weeks and usually do not scar unless secondarily infected.
In immunocompromised patients, lesions are more numerous, may have hemorrhagic bases, and heal more slowly. Visceral complications occur in 30–50% of severe cases and can be fatal. Adults typically experience more severe illness and have a higher risk of complications. Pregnant women are at increased risk of varicella pneumonia and may transmit infection to the fetus. Perinatal varicella (maternal infection 5 days before to 2 days after delivery) can result in severe neonatal disease with high mortality. Congenital varicella syndrome, occurring when infection develops in the first two trimesters, may cause limb hypoplasia, skin scarring, ocular abnormalities, and central nervous system impairment.
Diagnosis is primarily clinical, based on the characteristic rash. Laboratory confirmation can be obtained by PCR detection of VZV DNA from lesion specimens, which is the most reliable method. Viral culture, direct immunofluorescence staining, Tzanck smear (showing multinucleated giant cells), and serologic testing may also be used. Chest radiographs may show nodular or interstitial infiltrates in cases of varicella pneumonia.
Differential diagnosis includes disseminated herpes simplex infection, enteroviral rashes, scabies, dermatitis herpetiformis, folliculitis, atypical measles, and rickettsialpox.
Oral acyclovir is recommended within 24 hours of rash onset to reduce disease severity. In immunocompetent children aged ≥2 years and weighing ≤40 kg, the dose is 80 mg/kg/day divided into four doses (maximum 3200 mg/day) for 5 days. Older children and adults may receive 3200 mg/day in four divided doses for 5 days. Adequate hydration is important. Valacyclovir and famciclovir are alternatives for older children and adults. Supportive care includes bathing, antipruritic agents, trimmed fingernails to prevent excoriation, and acetaminophen for fever. Aspirin should be avoided due to the risk of Reye’s syndrome.
Passive immunization with varicella zoster immunoglobulin is recommended for high-risk susceptible individuals after exposure, including immunocompromised persons, pregnant women, certain premature infants, and newborns exposed perinatally. It should be administered ideally within 72 hours and no later than 96 hours after exposure.
Active immunization with the live attenuated varicella vaccine is part of routine childhood vaccination schedules. Two doses are recommended, beginning at 12–15 months of age, with a second dose at 4–6 years. Unvaccinated adolescents and adults without evidence of immunity should receive two doses separated by at least 28 days. Vaccination is contraindicated during pregnancy.
Prognosis in healthy children is excellent, and infection usually confers lifelong immunity. However, severe disease may occur in adults, immunocompromised patients, pregnant women, and neonates. The virus remains latent and may later reactivate as herpes zoster.
Complications include secondary bacterial skin infections (commonly due to staphylococci or group A streptococci), varicella pneumonia (particularly in adults and pregnant women), cerebellar ataxia, encephalitis, meningitis, transverse myelitis, myocarditis, nephritis, hepatitis, bleeding disorders, and Reye’s syndrome. Mortality is low in the post-vaccination era but remains significant in high-risk groups.
Chickenpox is a highly contagious febrile illness of childhood caused by primary infection with the varicella zoster virus (VZV). It is characterized by a generalized pruritic rash in which lesions at different stages of development—macules, papules, vesicles, pustules, and crusts—are present simultaneously.
The disease occurs worldwide and shows seasonal peaks in late winter and early spring. Before widespread vaccination, the primary attack rate in susceptible individuals was approximately 90%, with household secondary attack rates of 70–90%. Since implementation of routine vaccination programs, incidence, hospitalizations, complications, and deaths have declined dramatically. Both sexes are equally affected. Most cases occur in young children, although an increasing proportion of cases now occur in adolescents and adults in partially vaccinated populations.
Risk factors include close contact with an infected individual (varicella or herpes zoster), lack of immunity, and increasing age at exposure. Approximately 90% of individuals aged 15 years or older are immune, but 10% remain susceptible. Adults, pregnant women, and immunocompromised individuals are at higher risk for severe disease and complications.
Varicella zoster virus is a DNA virus (human herpesvirus 3) in the Herpesviridae family. Humans are the only known reservoir. Transmission occurs via respiratory droplets or direct contact with vesicular fluid. The virus enters through the respiratory mucosa, replicates in regional lymph nodes, and spreads through primary viremia. A secondary viremia disseminates the virus to the skin and other organs. After primary infection, the virus remains latent in sensory ganglia and may reactivate later in life as herpes zoster.
The incubation period is typically 10–14 days (range 10–21 days). Patients are infectious from approximately 48 hours before rash onset until all lesions have crusted. In immunocompetent children, mild prodromal symptoms such as malaise and low-grade fever may precede the rash by 1–2 days. The rash begins on the face and trunk and spreads centrifugally, sometimes involving mucous membranes. Lesions evolve rapidly from macules to papules and then to clear vesicles on an erythematous base. Vesicular fluid becomes turbid, crusting follows, and new crops of lesions appear over 2–4 days. Crusts fall off within 1–2 weeks and usually do not scar unless secondarily infected.
In immunocompromised patients, lesions are more numerous, may have hemorrhagic bases, and heal more slowly. Visceral complications occur in 30–50% of severe cases and can be fatal. Adults typically experience more severe illness and have a higher risk of complications. Pregnant women are at increased risk of varicella pneumonia and may transmit infection to the fetus. Perinatal varicella (maternal infection 5 days before to 2 days after delivery) can result in severe neonatal disease with high mortality. Congenital varicella syndrome, occurring when infection develops in the first two trimesters, may cause limb hypoplasia, skin scarring, ocular abnormalities, and central nervous system impairment.
Diagnosis is primarily clinical, based on the characteristic rash. Laboratory confirmation can be obtained by PCR detection of VZV DNA from lesion specimens, which is the most reliable method. Viral culture, direct immunofluorescence staining, Tzanck smear (showing multinucleated giant cells), and serologic testing may also be used. Chest radiographs may show nodular or interstitial infiltrates in cases of varicella pneumonia.
Differential diagnosis includes disseminated herpes simplex infection, enteroviral rashes, scabies, dermatitis herpetiformis, folliculitis, atypical measles, and rickettsialpox.
Oral acyclovir is recommended within 24 hours of rash onset to reduce disease severity. In immunocompetent children aged ≥2 years and weighing ≤40 kg, the dose is 80 mg/kg/day divided into four doses (maximum 3200 mg/day) for 5 days. Older children and adults may receive 3200 mg/day in four divided doses for 5 days. Adequate hydration is important. Valacyclovir and famciclovir are alternatives for older children and adults. Supportive care includes bathing, antipruritic agents, trimmed fingernails to prevent excoriation, and acetaminophen for fever. Aspirin should be avoided due to the risk of Reye’s syndrome.
Passive immunization with varicella zoster immunoglobulin is recommended for high-risk susceptible individuals after exposure, including immunocompromised persons, pregnant women, certain premature infants, and newborns exposed perinatally. It should be administered ideally within 72 hours and no later than 96 hours after exposure.
Active immunization with the live attenuated varicella vaccine is part of routine childhood vaccination schedules. Two doses are recommended, beginning at 12–15 months of age, with a second dose at 4–6 years. Unvaccinated adolescents and adults without evidence of immunity should receive two doses separated by at least 28 days. Vaccination is contraindicated during pregnancy.
Prognosis in healthy children is excellent, and infection usually confers lifelong immunity. However, severe disease may occur in adults, immunocompromised patients, pregnant women, and neonates. The virus remains latent and may later reactivate as herpes zoster.
Complications include secondary bacterial skin infections (commonly due to staphylococci or group A streptococci), varicella pneumonia (particularly in adults and pregnant women), cerebellar ataxia, encephalitis, meningitis, transverse myelitis, myocarditis, nephritis, hepatitis, bleeding disorders, and Reye’s syndrome. Mortality is low in the post-vaccination era but remains significant in high-risk groups.
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