Caused by the herpesvirus varicella zoster—the same virus that, in its latent stage, causes herpes zoster (shingles)—varicella is transmitted by direct contact (primarily with respiratory secretions; less commonly, with skin lesions) or indirect contact (airborne). The incubation period usually lasts 14 to 17 days but can be as short as 10 days and as long as 20 days. (See Incubation and duration of common rash-producing infections.) Varicella is probably communicable from 1 day before lesions erupt to 6 days after vesicles form, although it’s most contagious in the early stages of eruption of skin lesions.

Severe pruritus with this rash may provoke persistent scratching, which can lead to infection, scarring, impetigo, furuncles, and cellulitis. Rare complications include pneumonia, myocarditis, fulminating encephalitis (Reye syndrome), bleeding disorders, arthritis, nephritis, hepatitis, and acute myositis. Congenital varicella causes hypoplastic deformity and limb scarring, retarded growth, and central nervous system and eye manifestations.

The patient’s history reveals exposure within the past 2 to 3 weeks to someone with varicella. The infection produces distinctive signs and symptoms, notably a pruritic rash. During the prodromal phase, the patient has slight fever, malaise, and anorexia. Within 24 hours, the rash typically begins as crops of small, erythematous macules on the trunk or scalp. Macules progress to papules and then clear vesicles on an erythematous base (the so-called dewdrop on a rose petal). These vesicles become cloudy and break easily; then scabs form.