Chickenpox is an acute, systemic, usually childhood infection caused by the varicella-zoster virus (human herpesvirus type 3). It usually begins with mild constitutional symptoms that are followed shortly by skin lesions appearing in crops and characterized by macules, papules, vesicles, and crusting. Patients at risk of severe neurologic or other systemic complications (eg, pneumonia) include adults, neonates, and patients who are immunocompromised or have certain underlying medical conditions. Diagnosis is clinical. Those at risk of severe complications receive postexposure prophylaxis with immune globulin and, if disease develops, are treated with antiviral drugs (eg, valacyclovir, famciclovir, acyclovir). Vaccination provides effective prevention.
Chickenpox is caused by the varicella-zoster virus (human herpesvirus type 3); chickenpox is the acute invasive phase of the virus, and herpes zoster (shingles) represents reactivation of the latent phase (see Herpes Zoster). Chickenpox, which is extremely contagious, is spread by breathing infected droplets or by contact and is most communicable during the prodrome and early stages of the eruption. It is communicable from 48 h before the first skin lesions appear until the final lesions have crusted. Indirect transmission (by carriers who are immune) does not occur.
Epidemics occur in winter and early spring in 3- to 4-yr cycles. Some infants may have partial immunity, probably acquired transplacentally, until age 6 mo.
Symptoms and Signs
In immunocompetent children, chickenpox is rarely severe. In adults and immunocompromised children, infection can be serious. Mild headache, moderate fever, and malaise may occur 10 to 21 days after exposure, about 24 to 36 h before lesions appear. This prodrome is more likely in patients > 10 yr and is usually more severe in adults.
The initial rash, a macular eruption, may be accompanied by an evanescent flush. Within a few hours, lesions progress to papules and then characteristic, sometimes pathognomonic teardrop vesicles, often intensely itchy, on red bases. The lesions become pustular and then crust. Lesions initially develop on the face and trunk and erupt in successive crops; some macules appear just as earlier crops begin to crust. The eruption may be generalized (in severe cases) or more limited but almost always involves the upper trunk. Ulcerated lesions may develop on the mucous membranes, including the oropharynx and upper respiratory tract, palpebral conjunctiva, and rectal and vaginal mucosa. In the mouth, vesicles rupture immediately, are indistinguishable from those of herpetic gingivostomatitis, and often cause pain during swallowing. Scalp lesions may result in tender, enlarged suboccipital and posterior cervical lymph nodes. New lesions usually cease to appear by the 5th day, and the majority are crusted by the 6th day; most crusts disappear < 20 days after onset.
Sometimes vaccinated children develop varicella (called breakthrough varicella); in these cases, the rash is typically milder, fever is less common, and the illness is shorter; the lesions are infectious.
Secondary bacterial infection (typically streptococcal or staphylococcal) of the vesicles may occur, causing cellulitis or rarely necrotizing fasciitis or streptococcal toxic shock. Pneumonia may complicate severe chickenpox in adults, neonates, and immunocompromised patients of all ages but usually not in immunocompetent young children. Myocarditis, hepatitis, and hemorrhagic complications may also occur.
.One of the most common neurologic complications is acute postinfectious cerebellar ataxia, which occurs in 1/4000 cases in children. Transverse myelitis may also occur. Reye syndrome (see Reye's Syndrome), a rare but severe childhood complication, may begin 3 to 8 days after onset of the rash; aspirin increases the risk. In adults, encephalitis, which can be life threatening, occurs in 1 to 2/1000 cases of chickenpox.
Chickenpox is suspected in patients with the characteristic rash, which is usually the basis for diagnosis. The rash may be confused with that of other viral skin infections. If the diagnosis is in doubt, laboratory confirmation can be done; it requires PCR for viral DNA, immunofluorescent detection of viral antigen in lesions or culture, or serologic findings. Samples are generally obtained with scraping and transported to the laboratory in viral media.
Chickenpox in children is rarely severe. Severe or fatal disease is more likely in adults, patients with depressed T-cell immunity (eg, lymphoreticular cancer), and those receiving corticosteroids or chemotherapy.
Mild cases in children require only symptomatic treatment. Relief of itching and prevention of scratching, which predisposes to secondary bacterial infection, may be difficult. Wet compresses or, for severe itching, systemic antihistamines and colloidal oatmeal baths may help. Simultaneous use of large doses of systemic and topical antihistamines can cause encephalopathy and should be avoided.
To prevent secondary bacterial infection, patients should bathe regularly and keep their underclothing and hands clean and their nails clipped. Antiseptics should not be applied unless lesions become infected; bacterial superinfection is treated with antibiotics.
Oral antivirals, when given to immunocompetent patients within 24 h of the rash's onset, slightly decrease symptom duration and severity. However, because the disease is generally benign in children, antiviral treatment is not routinely recommended. Oral valacyclovir, famciclovir, or acyclovir should be given to healthy people at risk of moderate to severe disease, including all patients ≥ 12 yr and those with skin disorders (particularly eczema) or chronic lung disease. The dose is famciclovir 500 mg tid or valacyclovir 1 g tid. Acyclovir is a less desirable choice because it has poorer oral bioavailability, but it can be given at 20 mg/kg qid with a maximum daily dose of 3200 mg. Immunocompromised children > 1 yr should be given 500 mg/m2 q 8 h IV. Immunocompromised adults should be treated with acyclovir 10 to 12 mg/kg IV q 8 h.
Patients should not return to school or work until the final lesions have crusted.
Infection provides lifelong protection. Potentially susceptible people should take strict precautions to avoid people capable of transmitting the infection. Susceptible health care workers who have been exposed to varicella should be vaccinated as soon as possible and kept off duty for 21 days.
All healthy children and susceptible adults should receive 2 doses of live-attenuated varicella vaccine (see Recommended Immunization Schedule for Ages 0–6 yr and see Recommended Immunization Schedule for Ages 7–18 yr). Vaccination is particularly important for women of child-bearing age and adults with underlying chronic medical conditions. Serologic testing to determine immune status before vaccination in adults is usually not required. Although the vaccine may cause chickenpox in immunocompetent patients, disease is usually mild (< 10 papules or vesicles) and brief and causes few systemic symptoms.
Vaccination is contraindicated in
After exposure, chickenpox can be prevented or attenuated by IM administration of varicella-zoster immune globulin, which is available as an investigational new drug from FFF Enterprises (800-843-7477). Candidates for postexposure prophylaxis include people with leukemia, immunodeficiencies, or other severe debilitating illness; susceptible pregnant women; and neonates whose mother developed chickenpox within 5 days before or 2 days after delivery. Neonates born at ≥ 28 wk and exposed to a nonmaternal source do not need immune globulin if their mother has evidence of immunity, but neonates born at < 28 wk do. The immune globulin should be given as soon as possible (and within 10 days of exposure) and may modify or prevent varicella. Vaccination should be given as soon as possible to susceptible healthy patients eligible for vaccination, and vaccination can be effective in preventing or ameliorating disease within 3 days and possibly up to 5 days after exposure.
To prevent nosocomial transmission, the Centers for Disease Control and Prevention (CDC) recommends postexposure prophylaxis with vaccination or varicella-zoster immunoglobulin, depending on immune status, for exposed health care workers and patients without evidence of immunity (available at Immunization of Health-Care Personnel ).
Last full review/revision April 2013 by Kenneth M. Kaye, MD
Content last modified September 2013