Description

• Common, highly contagious generalized exanthem characterized by the development of crops of pruritic vesicles on the skin and mucous membranes
• Fever in up to 70% of persons

• Virus is spread by respiratory (airborne) droplets, direct contact with varicella vesicles, or, rarely, zoster lesions.
• Virus establishes latency in the dorsal root ganglia; reactivation results in herpes zoster or “shingles.”
• Outbreaks tend to occur late winter to early spring in temperate climates.
• Usual incubation period is 14–16 days (range, 10–21). Patients are infectious from ~48 hours before appearance of the rash until the final lesions have crusted. Historically, most people acquire chickenpox during childhood and develop lifelong immunity:
  • Now it is an immunizable disease.
• System(s) affected: Nervous; Skin/Exocrine
• Synonym(s): Varicella

Epidemiology

• Predominant age: Peak incidence preschoolers to 9 years, but may occur at any age
• Predominant gender: Male = Female

• Decreasing incidence since vaccine available: Estimated at 3.5 million cases annually prior to vaccine introduction, with an incidence rate of 8–9% in children age 1–9 years. Reported US varicella cases 1991: 147,076; reported for 2010: 15,427, provisionally reported for 2011: 12,041 cases (1,2)
• Prior to vaccine availability, ~100 deaths/year were reported in the US; for 2010, only 4 deaths were reported (1).
• US rates: 1994, prior to vaccine: 135.76/100,000 persons; 2009: 8.71/100,000 persons (1)
• Rates in the US had dropped continuously after vaccine development until mid-2000s when they evened out; 2nd dose of vaccine recommended in 2006, and rates again have declined year by year (1).

Risk Factors

• No prior history of varicella infection
• Immunosuppressed patients (especially children with leukemia/lymphoma in remission or receiving high-dose corticosteroids)

• Infection more severe in adults than in children
• Latent varicella infection may reactivate and cause the exanthem known as shingles or zoster.
• Herpes zoster vaccine, a live attenuated vaccine licensed in 2006, is now recommended for persons ≥60 years to prevent zoster (shingles): FDA-approved for those ≥50 years:
  • 1-time dose. Recommended for those previously infected with varicella (chickenpox); those never infected should receive regular varicella vaccine. Dose: 0.65 mL SQ, available as single-dose vial.
  • Advisory Committee on Immunization Practices (ACIP) recommends routine vaccination of all persons aged >60 years with 1 dose of zoster vaccine. It is not necessary to ask patients about their history of varicella (chickenpox) or to conduct serologic testing for varicella immunity.
  • Most common cause of death: Primary viral pneumonia

• Neonates born to mothers who develop chickenpox from 5 days before to 2 days after delivery are at risk for serious disease. Must give varicella-zoster immune globulin.
• Varicella bullosa seen mainly in children <2 years. Lesions appear as bullae instead of vesicles. The clinical course does not change.
• Most common cause of death: Septic complications and encephalitis
• Avoid aspirin/acetylsalicylic acid in children because of link to Reye syndrome.

• 25% risk of transplacental infection after maternal infection
• Congenital malformations are seen in 2% of patients when the fetus is infected during the 1st or 2nd trimesters, characterized by limb atrophy and scarring of the skin of the extremities and occasional CNS and eye manifestations.
• Morbidity is increased in women infected during pregnancy (e.g., pneumonia).

General Prevention

• Exposed, susceptible people should be considered at risk and potentially infectious for 21 days.
• Isolate hospitalized patients.
• Passive immunization with IM varicella-zoster immune globulin given within 96 hours of exposure, but recently approved for 10 days after exposure (3):
  • Recommended for people exposed to chickenpox or shingles who are immunocompromised, newborns of mothers with onset of chickenpox <5 days before delivery or <2 days after delivery, premature infants (<28 weeks) exposed in neonatal period either whose mothers are not immune, or babies who weigh <1,000 g regardless of mom's immunity (3).
• Active immunization after exposure: Shown to prevent or reduce significantly the severity of varicella if given within 72 hours postexposure
• Active immunization: Varicella virus vaccine (Varivax): Live attenuated vaccine approved by FDA in 1995 for pediatrics immunization and recommended by ACIP for immunization of healthy patients ≥12 months who have not had chickenpox:
  • 12 months–12 years: Initial dose 0.5 mL SC at age 12–15 months; 2nd dose age 4–6 years. Prelicensure studies showed efficacy rates: 70–90% against any disease and 95% against severe disease 7–10 years after vaccination. Other studies showed 100% efficacy at 1 year and 98% at 2 years after vaccination. More recent studies show rates of 85–94% effectiveness, the higher end for the prevention of severe disease. The 2-dose regimen is even more effective, with rates of 96–98% effectiveness. Breakthrough disease generally has <50 lesions, shorter duration of illness, and lower incidence of fever (4)[A].
  • ≥13 years: Two 0.5 mL SC doses 4–8 weeks apart, seroconversion rates 78–82% after 1 dose, 99% after 2 doses. Adults have efficacy rates in the lower end of this range.
  • Estimated 2-dose vaccine coverage in the US for 2009 in children ages 19–35 months: 89.6%
  • Vaccine side effects are pain and redness at vaccine site.
  • Vaccine contraindications (5):
    • Severe allergic reaction (e.g., anaphylaxis) to a previous dose or vaccine component
    • Severe immunodeficiency (e.g., severely immunocompromised HIV patients, on chemotherapy, congenital immunodeficiency, or long-term immunosuppressive therapy)
    • Pregnancy
• Newly approved MMRV vaccine, which combines the measles, mumps, and rubella vaccine with varicella, is equally effective. There are rare reports of an increased risk of febrile seizures 5–12 days after vaccination in 1/2,300–2,600 patients (6)[A].
• May be considered for a subset of HIV-positive children in CDC class I with CD4 >25%:
  • Vaccine recipients should avoid contact with immunocompromised people and pregnant women who have never had chickenpox and their newborns, for up to 6 weeks after vaccination.
  • Children needing catch-up vaccination need at least 3 months between doses 1 and 2.

Pathophysiology

• Skin lesions identical histologically to those of herpes simplex virus
• In fatal cases, intranuclear inclusions can be found in the endothelium of blood vessels and most organs.

Etiology

• Varicella-zoster virus is a member of the α-Herpesviridae subfamily; a double-stranded DNA virus.
• Reservoir is humans