Varicella (chickenpox) is an acute, highly contagious disease caused by varicella-zoster virus (VZV), a member of the herpesvirus family. Only one serotype of VZV is known, and humans are the only reservoir. Infection results in lifelong immunity. Approximately 95% of women born in the United States have VZV antibodies by the time they reach reproductive age. The incidence of VZV infection during pregnancy has been reported as up to 7:10,000.
VZV transmission occurs via droplets, aerosols, or direct contact with respiratory secretions, and almost always produces clinical disease in susceptible individuals. While mostly a mild disorder in childhood, varicella tends to be more severe in adults. It may be fatal, especially in neonates and in immunocompromised persons. In temperate climates most cases occur before the age of 10. Varicella is characterized by an itchy, rash usually starting on the scalp and face and initially accompanied by fever and malaise. The rash gradually spreads to the trunk and extremities. The vesicles gradually dry out and crusts appear which then disappear over a period of one to two weeks.
The infection may occasionally be complicated by pneumonia or encephalitis (inflammation of the brain), at times with serious or fatal consequences. Shingles is a painful rash that may occasionally result in permanent damage to the nerves or visual impairment. It is relatively common in HIV-infected persons, sometimes with fatal consequences.
Symptoms and Signs
The incubation period for this infection is 10–20 days. A primary infection follows and is characterized by a flu-like syndrome with malaise, fever, and development of a pruritic maculopapular rash on the trunk, which becomes vesicular and then crusts.
Pregnant women are prone to the development of VZV pneumonia, often a fulminant infection sometimes requiring respiratory support. After primary infection, the virus becomes latent, ascending to dorsal root ganglia. Subsequent reactivation can occur as zoster, often under circumstances of immunocompromise, although this is rare during pregnancy.
Two types of fetal infection have been documented. The first is congenital VZV syndrome, which typically occurs in 0.4–2% of fetuses exposed to primary VZV infection during the first trimester. Anomalies include limb and digit abnormalities, microphthalmos, and microcephaly.
Infection during the second and third trimesters is less threatening. Maternal IgG crosses the placenta, protecting the fetus. The only infants at risk for severe infection are those born after maternal viremia but before development of maternal protective antibody. Maternal infection manifesting 5 days before or up to 2 days after delivery is the time period believed to be most hazardous for transmission to the fetus.
Diagnosis is commonly made on clinical grounds. Laboratory verification is made by ELISA, fluorescent antibody, and hemagglutination inhibition antibody techniques. Serum obtained by cordocentesis may be tested for VZV IgM to document fetal infection.
Varicella-zoster immune globulin (VZIG) has been shown to prevent or modify the symptoms of infection in exposed persons. Treatment success depends on identification of susceptible women at or just following exposure. Exposed women with a questionable or negative history of chickenpox should be checked for antibody, since the overwhelming majority will have been previously exposed. If the antibody is negative, VZIG (625 units intramuscularly) should ideally be given within 96 hours of exposure for greatest efficacy, but the CDC reports it can be given for up to 10 days.
There are no known adverse effects of VZIG administration during pregnancy, although the incubation period for disease can be lengthened. Infants born to women in whom symptoms develop in the period from 5 days before delivery to 2 days after delivery should also receive VZIG (125 units).
Pregnant women with varicella may benefit from treatment with oral acyclovir if started within 24 hours of rash onset. Treatment has been shown to improve maternal symptoms but does not prevent congenital varicella. Infected pregnant women should be closely observed and hospitalized at the earliest signs of pulmonary involvement. Intravenous acyclovir (10 mg/kg intravenously every 8 hours) is recommended in the treatment of VZV pneumonia.