ABSTRACT
Primary varicella-zoster virus (VZV) infection produces varicella (chicken pox), a highly contagious but typically mild disease of childhood. An estimated 4 million cases occurred annually in the United States before 1995, 90% of them in individuals 1-14 years of age [1]. By adult life, nearly everyone in North America is seropositive. In northern regions
only 2% of varicella occurs after age 20, but in tropical climates a higher incidence of varicella is seen in adults [2,3]. In temperate climates, the incidence of varicella peaks semiannually, usually in the spring, with another, smaller peak in winter [4,5]. Disease is presumed to be transmitted by direct contact or aerosols containing virus [6-8]. Respiratory infection is probably followed by viral replication in the pharynx and regional lymph nodes [9-11]. The incubation period in healthy children is 9-21 days [5,9,10]. Viremia in immunocompetent varicella patients has been demonstrated 1-11 days prior to rash [12,13], with virus located predominantly in lymphocytes [14-16]. Fever, myalgia, and arthralgia precede or coincide with rash. The exanthem of chickenpox consists of macules and papules that develop into vesicles surrounded by an erythematous halo. Vesicles that reflect degenerative changes of the corium and dermis develop quickly and are characterized by multinucleated giant cells and intranuclear Cowdry type A inclusions [17], a hallmark of herpesvirus family infection. Vesicles contain abundant infectious virus that can be isolated in cell culture [18]. Rash usually begins on the trunk, then spreads to the face, limbs, and often to the buccal and pharyngeal mucosa. Eventually, vesicles burst and their fluid hardens, a process known as ‘‘crusting.’’ New vesicles from within the first 4 days after outbreak, whereas crusting begins after 2-3 days; thus, crusting and fresh vesicles may be seen simultaneously. Patients are considered infectious from 2 days before rash until all vesicles have crusted, typically 6 days after the onset of rash. Although most individuals can recount only a single episode of varicella, immunological evidence indicates that subclinical reinfection with VZV is common [19,20]. Immunization of children 12-18 months old with a live attenuated varicella vaccine (Oka strain) may eventually shift the average age of infection to older susceptible individuals [21].
