ETIOLOGICAL AGENT:

    Human herpesvirus 3 (Varicella-zoster virus)
 

THE DISEASE:

    Chickenpox is a highly contagious, acute exanthematous disease that is most common in childhood. It is characterized by successive crops of lesions that progress rapidly from macules and papules to vesicles, pustules and crusts. In children, chickenpox is generally a mild disease with few complications. When acquired by adults, however, it is often associated with high fever, severe constitutional symptoms and pulmonary involvement. There is a mild prodrome.
 

PATHOGENESIS:

    Man is the only known host. The virus is spread from person to person by droplet inhalation or direct contact. The initial site of virus replication is unknown but subsequently there is a viremia with subsequent skin lesions. The early papular lesions are minute vacuoles surrounded by ballooning degeneration of epithelial cells within the prickle cell layer of the epidermis. In a few hours edema fluid accumulates, elevating the stratum corneum to form a clear vesicle, while multinucleated giant cells, containing eosinophilic intranuclear inclusions, form among the cells at the edges and base of the lesion. As the vesicles begin to dry, they become filled with a cloudy, fibrinous fluid containing leukocytes and desquamated epidermal cells. The final stages of lesion formation are characterized by crusting along with regeneration of the epithelial cells.
 

DIAGNOSIS:

    This is based on:

        1.     Mild prodrome (malaise and fever)

        2.     Lesions that evolve from small red macules to papules, vesicles, then pustules that crust.
                The vesicles are variable in size and shape. They are filled with straw-colored fluid and
                are surrounded at the base by an intense red corona of inflammation. They lie on, rather
                than in, the skin.

        3.     Distribution of lesions with a central concentration, presenting first and in greatest
                abundance on the trunk, then the neck, face and proximal extremities. Lesions can occur
                on palms, soles and mucous membranes.

        4.     Lesions are painless and pruritic

        5.     Mild fever (100°F)

        6.     Presence of multinucleated giant cell with nuclear inclusions

        7.     Serology

        8.     Crops of lesions
 

TREATMENT:

    None indicated unless case is severe, then administer acyclovir (Zovirax).
 

PREVENTION:

    A new improved vaccine (Varivax, Merck & Co.) was approved in 1995. This is a live attenuated virus vaccine. A single 0.5 ml dose is given subcutaneously to children between 1-12 years of age. Patients 13 years of age or older should be given a 0.5 ml dose subcutaneously followed by a second 0.5 ml subcutaneous dose four-eight weeks later. The outer aspect of the upper arm (deltoid) is the preferred site of injection.
 

COMPLICATIONS:

    1.     Reye's syndrome (fatty liver with encephalopathy) - varicella is the antecedent event in 20%
            of the cases of Reye's syndrome, a condition that has been associated with the
            administration of salicylates to children with viral disease. Reye's syndrome begins with
            vomiting and a change in sensorium after the skin lesions have healed. This is followed by
            signs of hepatic injury, hypoglycemia and extensive fatty vacuolization of renal tubules
            and liver.

    2.     Zoster (shingles) - peripheral neuritis