A 12-year-old girl presents with a 3-day history of a body-wide pruritic vesicular rash (Figure 108-1). The episode started 24 hours before the rash with fever and malaise. The patient is diagnosed with varicella and no antiviral medications are given. Acetaminophen or ibuprofen are recommended for fever and comfort, avoiding aspirin to prevent Reyes syndrome.

Varicella (chickenpox) is a highly contagious viral infection that can become reactivated in the form of zoster.

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  Varicella-zoster virus (VZV) is distributed worldwide.

  
  
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  The rate of secondary household attack is more than 90 percent in susceptible individuals (Figure 108-2).¹

  
  
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  Adults and immunocompromised patients generally develop more severe disease than normal children.

  
  
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  Traditionally, primary infection with VZV occurs during childhood (Figure 108-3). In childhood, it is usually a benign, self-limited illness in immunocompetent hosts. It occurs throughout the year in temperate regions, but the incidence peaks in the late spring and summer months.

  
  
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  Neonatal varicella is a serious illness with a mortality rate up to 30 percent.² The risk of infection and the case fatality rate are significantly increased if a mother has symptoms less than five days prior to delivery. The time to delivery allows insufficient time for the development of maternal IgG and passive transfer of protection to the fetus.³ Postnatally acquired varicella that occurs beyond 10 days after birth usually is mild.⁴

  
  
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  Prior to the introduction of the varicella vaccine in 1995, the yearly incidence of chickenpox in the US was approximately 4 million cases with approximately 11,000 hospital admissions and 100 deaths.⁵

  
  
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  As the vaccination rates steadily increased in the US, there has been a corresponding fourfold decrease in the number of cases of chickenpox cases down to disease rates of from 0.3 to 1.0 per 1000 population in 2001.⁵

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  Chickenpox is caused by a primary infection with the VZV, which is a double-stranded, linear DNA herpesvirus.

  
  
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  Transmission occurs via contact with aerosolized droplets from nasopharyngeal secretions or by direct cutaneous contact with vesicle fluid from skin lesions.

  
  
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  The incubation period for VZV is approximately 15 days, during which the virus undergoes replication in regional lymph nodes, followed by two viremic phases, the second of which persists through the development of skin lesions generally by day 14.⁶

  
  
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  The vesicular rash appears in crops for several days. The lesions start as vesicle on a red base, which is classically described as a dewdrop on a rose petal (Figure 108-4). The lesions gradually develop a pustular component (Figure 108-5) followed by the evolution of crusted papules (Figure 108-6). The period of infectivity is generally considered to last from 48 hours prior to the onset of rash until skin lesions have fully crusted.

  
  
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  The most frequent complication in healthy children is bacterial skin superinfection (Figure 108-6). Less common skin complications (seen more frequently in immunosuppressed hosts) include bullous varicella, purpura fulminans, and necrotizing fasciitis.

  
  
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  Encephalitis is a serious potential complication of chickenpox that develops toward the end of the first week of the exanthema. One form, acute cerebellar ataxia, occurs mostly in children and is generally followed by complete recovery. A more diffuse encephalitis most often occurs in adults and may produce delirium, seizures, and focal neurologic signs. It has significant rates of long-term neurologic sequelae and death.

  
  
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  Pneumonia is rare in healthy children but accounts for the majority of hospitalizations in adults, where it has up to a 30 percent mortality rate.⁷ It usually develops insidiously within a few days after the rash has appeared with progressive tachypnea, dyspnea, and dry cough. Chest x-rays reveal diffuse bilateral infiltrates. Treat with prompt administration of intravenous acyclovir. The use of adjunctive steroid therapy is controversial.

  
  
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  Varicella hepatitis is rare, and typically only occurs in immunosuppressed individuals. It is frequently fatal.

  
  
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  Reactivation of latent VZV results in herpes zoster or shingles.