Varicella (chicken pox) is an acute communicable disease, primarily of childhood, caused by Herpesvirus varicellae (the varicella-zoster virus). The incubation period ranges from 10 to 21 days, with a median of 12 to 14 days. Susceptibility is universal, and because varicella is one of the most highly communicable infections known, the disease is almost universal as well. Diagnosis is relatively easy because of the characteristic vesicular rash. The principal route of spread appears to be by aerosolized small droplet rather than by direct contact with vesicular fluid or with the dried crusts of the skin lesions; paradoxically, virus is difficult to detect in oropharyngeal secretions, but is present in high titer in vesicular fluid from the lesions (Weller, 1982).

In normal children other than neonates, varicella is almost always a benign illness. Encephalitis occurs occasionally, but the most serious apparent complication is Reye’s syndrome. Although the nature of the relationship between varicella and Reye’s syndrome is uncertain, it is clear that varicella either plays a direct role in the pathogenesis of the syndrome or acts as a surrogate or marker for some concurrent condition that predisposes children to the disorder.

Adults are much more likely to experience significant morbidity or even mortality due to varicella. Varicella pneumonia, which may or may not be complicated by secondary bacterial pneumonia, is the principal complication in adults, although encephalitis also occurs.

Varicella-zoster virus shares with other members of the herpesvirus group the property of persistence or latency. In the case of varicella-zoster, the sensory ganglia have been suggested as the principal site of latency, but this has not been proved (Weller, 1982). Reactivation of the virus secondary to advancing age, stress, immunosuppression, and perhaps other factors, results in herpes zoster (shingles), a painful and prolonged eruption of typical herpetic lesions involving