Initial exposure to the Varicella-Zoster virus produces chicken pox. This is a common, highly contagious childhood disease which occasionally affects young adults. The incubation period averages about fifteen days; fever, headache, and malaise develop about twenty-four hours before the rash appears. The rash starts as pink spots or bumps, which rapidly evolve into small, clear blisters producing the characteristic "dew drop on a rose petal." These blisters become filled with pus and crust over within a day. The disease is no longer contagious when the rash is dried and crusted. Much of the eruption is on the face, scalp and trunk, with the extremities also involved. Lesions may occur in the mouth and throat, causing pain on swallowing. I

Only a small number of adults are susceptible to chicken pox. In urban areas, 85 percent of the population have had chicken pox by the age of nine and therefore are no longer susceptible. When adults get chicken pox they tend to be sicker than children who have it. Pneumonitis (lung involvement) is frequent in adults and usually, but not always, mild. Secondary bacterial infection of the rash can be a problem and may be caused by scratching.