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Varicella: Varicella Zoster Virus
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Varicella is a highly communicable viral disease with worldwide distribution. In temperate climates of the Northern Hemisphere, varicella occurs mainly in the period from late winter to early spring. Secondary attack rates reach close to 90% in susceptible household contacts. Varicella-zoster virus (VZV) is the causative agent and is transmitted by droplets, aerosol or direct contact, and patients are usually contagious from a few days before rash onset until the rash has crusted over. Once a case has occurred in a susceptible population, it is very hard to prevent an outbreak. As subclinical infection is rare, the disease is experienced by almost every human being.
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Varicella (chickenpox) is the primary infection with the varicella zoster virus (VZV). It is a highly contagious rash illness transmitted by airborne or droplet pathways. The usual incubation period is 14-16 days (range 10-21 days). Second cases of varicella have been reported in immunocompetent persons but are rare. Following varicella, VZV establishes latency in sensory nerve ganglia. The virus can reactivate later in life, causing herpes zoster (shingles), usually localized to one to three dermatomes.
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Varicella Zoster Virus (VZV) causes herpes zoster, or shingles, which is a skin rash often with painful blisters, and is the same virus that causes chickenpox. Anyone who has had chickenpox can develop shingles because VZV remains dormant in the nerve cells and may re-emerge many years later causing the illness. Shingles may affect any age group but occurs most frequently in adults 60 years of age and older and the immunocompromised. The illness is common, resulting in over one million cases in the United States each year. The primary complication of shingles includes acute pain, called post-herpetic neuralgia (PHN), and occurs in approximately 65% of affected patients. Shingles-associated pain may last months, or even years, and can have a negative impact on quality of life.
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Varicella vaccine has been demonstrated to be very effective. Prelicensure, controlled, clinical trials demonstrated varicella vaccine to be 70% to 90% effective for preventing varicella and more than 95% effective for preventing severe varicella.13,14 A postlicensure study of 148children performed during an outbreak of varicella in a child care center in DeKalb County, GA, found that varicella vaccine was 86% (95% confidence interval [CI], 73%-92%) effective for preventing varicella and 100% (95% CI, 96%-100%) effective for preventing moderate to severe disease. Varicella was less severe and resulted in fewer days of absence from the day care center among immunized compared with unimmunized cases.15 Two more recent studies found that varicella vaccine was 86% (95%CI, 67%-94%) and 84% effective (95% CI, 60%-94%), respectively, for preventing varicella and 100% effective for preventing severe varicella.16,17 "Breakthrough" disease following exposure to wild-type varicella-zoster virus (VZV) occurs in about 1% to 4% of vaccinees per year, and the rate does not seem to increase with length of time after immunization.18 "Breakthrough" disease is usually of short duration and mild with fewer than 50lesions and low-grade or no fever.
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Varicella (chickenpox) is an infectious disease caused by varicella zoster virus. The incidence of chickenpox in adults has increased in recent years, with an increment in morbidity and mortality. [1] Pneumonia is the most common and the most serious complication of chickenpox infection in healthy adults. The exact frequency of pneumonia in patients with chickenpox has been difficult to determine and most published studies represent either collections of small case series or retrospective chart review over many years. [2] However, it is estimated to occur in one out of 400 cases of chickenpox infection. [3] Risk factors for developing pneumonia include impaired immune status, chronic lung diseases, being previous or current smokers, history of contact with a patient with chickenpox, as well as severity of the skin rash.
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Varicella, commonly known in the United States as chickenpox, is caused by the varicella-zoster virus. The disease is generally regarded as a mild, self-limiting viral illness with occasional complications. Before vaccination for varicella became widespread in the United States, this disease caused as many as 100 deaths annually. Since the varicella vaccine was introduced in the United States in 1995, disease incidence has substantially decreased.
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Varicella Zoster Virus