Primary infection caused by varicella-zoster virus (VZV) is manifest by varicella (chickenpox), while reactivation of latent virus causes herpes zoster (shingles). In immunocompetent children, varicella is usually not a serious disease, but can cause severe morbidity and mortality in adults and in immunocompromised individuals. Similarly, herpes zoster is associated with much greater morbidity in patients with impaired cell-mediated immune responses. In addition, herpes zoster can cause prolonged pain (postherpetic neuralgia) that can be very difficult to manage, particularly in older individuals. The outcomes of varicella and herpes zoster, especially in immunocompromised patients, have been dramatically improved by the development of safe and effective antiviral drugs with potent activity against VZV. Early drugs with modest efficacy and substantial toxicity (e.g., interferon, vidarabine, etc.) have been replaced by antiviral agents with enhanced in vitro activity, improved pharmacokinetic properties, and excellent safety profiles.
Most experienced physicians will be able to make an accurate clinical diagnosis of chickenpox based on the distinctive appearance of the skin lesions (Fig. 65.1(a)). The clinical syndrome of a child with mild constitutional symptoms, the typical diffuse vesicular rash, and no prior history of chickenpox is strongly suggestive of the diagnosis, especially if there has been exposure to VZV within the previous two weeks. However, in countries where the incidence of varicella is dramatically declining (such as the United States), younger physicians will have fewer opportunities to see patients with chickenpox and may feel less confident with the clinical diagnosis.