VARICELLA
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.
