The varicella-zoster virus (VZV) causes two discrete clinical infections: chickenpox (varicella) and herpes zoster (shingles). Although chickenpox was once a universal infection of childhood, the incidence of this disease has plummeted since the advent of the chickenpox vaccine. VZV belongs to the herpesvirus family and is primarily a respiratory disease with skin manifestations.
Clinical Findings: The disease is seen predominantly in children and young adults. Disease in adults tends to be more severe. Varicella is caused by inhalation of the highly infectious viral particle from an infected contact. The virus replicates within the pulmonary epithelium and then disseminates via the bloodstream to the skin and mucous membranes. Most children do not have severe pulmonary symptoms. A prodrome of headache, fever, cough, and malaise may precede the development of the rash by a few days.
The rash of varicella is characteristic and is present in almost 100% of those infected. It begins as a small, erythematous macule or papule that vesiculates. After vesiculation, the lesion may form a small vesiculopustule and then quickly rupture and form a thin, crusted erosion. The resulting vesicle has a central depression or dell, and it is localized over a red base. This gives rise to the classic description of a “dew drop on a rose petal.” The rash is more common on the trunk and on the head and neck, and it often is less severe when found on the extremities. A characteristic finding is an enanthem. The mucous membranes of the mouth are frequently involved with pinpoint vesicles with a surrounding red halo. A clinical clue to the diagnosis is the finding of lesions of multiple morphologies occurring at the same time. Most cases of varicella are self-resolving and heal with minimal to no scarring. Scarring can be significant if the vesicles or crusts become secondarily infected. Children are considered infectious from 1 to 2 days before the rash breaks out until the last vesicle crusts over. The diagnosis of chickenpox is made clinically. A Tzanck test, direct immunofluorescence, or viral culture can be used in nonclassic cases to confirm the diagnosis. Adults who develop primary varicella infection are at risk for severe pulmonary complications and severe skin disease with a dramatically increased risk for scarring. Adults who are exposed to VZV for the first time are more likely to develop pneumonia and encephalitis. Children who develop pneumonia during an infection with chickenpox have most likely acquired a secondary bacterial pneumonia.
Since the universal adoption in the United States of routine childhood vaccination against varicella in 1995, the incidence of varicella has precipitously dropped. The VZV vaccine is a live attenuated vaccine that is highly effective in achieving protective titer levels. Those individuals who develop chickenpox after vaccination have an attenuated course that is manifested by a few vesicles and more macules. This atypical variant of chickenpox is often misdiagnosed, or it may be so mild that the parents do not seek medical care.
Histology: A skin biopsy of a vesicle shows an intraepidermal blister that forms via ballooning degeneration of the keratinocytes. There is a perivascular lymphocytic infiltrate in the dermis. Multinucleated giant cells can be seen at the base of the blister.
Pathogenesis: Varicella (chickenpox) is caused by VZV. This is a double-stranded DNA virus with a lipid capsule. It is spread from human to human via the respiratory route. Once inhaled, the highly infectious virus invades endothelial cells in the respiratory tract. The virus quickly disseminates to the lymphatic tissue and then to other organ systems. This virus is neurotrophic and can lie dormant in the dorsal root ganglion, with the potential to reactivate much later in the form of shingles.
Treatment: Most childhood infections require no specific therapy other than supportive care and treatment of secondary bacterial infection. Immuno-compromised individuals, including pregnant women, should be treated with an antiviral medication such as acyclovir. Neonates are also at high risk for serious disease and need to be treated. The vaccine provides long-term effectiveness that has been shown to last for decades. More time is needed to firmly establish the need for and timing of any booster vaccinations.