Varicella-zoster virus (VZV) is a member of the herpesvirus group. Infection is spread through direct contact with skin lesions or through droplet inhalation. The incubation period is about 14 days (range, 9-21 days). Primary infection is usually varicella (chickenpox). The period of skin rash lasts about 4-6 days. This may be preceded by a short prodromal period. The period of contagion is said to be from 2 days before the rash until no new skin lesions appear and all old ones become crusted. Usually there is lifelong immunity to new infection (although not always). Complications are not common but are not rare. They include pneumonia, encephalitis, and Reye’s syndrome (20%-30% of Reye’s syndrome follows varicella infection). Incidence and severity of complications are increased in immunocompromised persons. Twenty-three percent to 40% of bone marrow transplant patients develop primary VZV infection or reinfection. Varicella infection in pregnancy may affect the fetus in 5%-10% of cases.

After the varicella syndrome is over, the virus begins a latent period in sensory nerve ganglion cells. Later on, it may reactivate in the form of zoster. Reactivation is more common in persons with malignancy or in those who are immunocompromised. It becomes more frequent with increasing age. About 10%-20% of the population is affected. Neuralgia is the most frequent symptom. A rash is also relatively frequent, often in the distribution of a dermatome. Encephalitis, sensory and motor neurologic abnormality, and ocular abnormality may occur.

Laboratory tests include Tzanck test smears of varicella-zoster lesions. Sensitivity is said to be 50% or less in varicella and 80% or less in zoster. This procedure is described in the section on simplex and the microscopic appearance is the same. Culture of lesions can be done, but results in varicella are reported to be 34%-78% positive and in zoster to be 26%-64%. Serologic tests can be done using fluorescent antibody (FA), ELISA, and slide LA. EIA is said to be 50% sensitive (range, 36%-94%); FA, about 75% (range, 69%-93%); and LA, about 60% (52%-76%). It appears that antibody production (and, therefore, sensitivity) is greater in otherwise healthy children than in adults. IgM antibody rises in varicella about 5-6 days after the rash begins and peaks at about 14 days; it rises in zoster about 8-10 days after onset of the rash and peaks at about 18-19 days. Some patients with VZV infection who later are infected by herpesvirus type 1 experience an anamnestic rise in VZV antibody. Nucleic acid (DNA) probe methods have also been reported for skin lesions and for CSF specimens.