Varicella zoster virus

Varicella zoster virus (VZV) causes varicella, the most common exanthematous disease of childhood. After the acute infection, VZV remains latent in the dorsal root ganglia; reactivation of the virus later in life causes zoster. VZV is ubiquitous, and humans are the only known host. It is estimated that there are 4 million cases per year in the United States, of which 90% occur in children between the ages of 1 and 14 years. Seropositivity reaches 95% by the late teen years and is close to 100% by age 60. The virus is highly contagious, with secondary household infection rates of about 80% to 90%. In temperate climates, a seasonal peak occurs between March and May. There are approximately 6,500 to 9,000 hospitalizations and 100 to 200 deaths in the United States annually from varicella or its complications. Approximately 300,000 cases of zoster are reported annually to the Centers for Disease Control and Prevention (CDC).

The primary source of infectious material is the fresh cutaneous lesion, which is teeming with virus. Unlike the poxviruses, VZV does not persist in scabs or crusts. It generally is believed that the period of communicability begins 1 to 2 days before the onset of rash and persists for 5 days or until skin lesions are crusting. The incubation period for varicella is approximately 14 days, but it can be as short as 10 or as long as 21 days. VZV infection also can be spread from zoster lesions to susceptible hosts, although the incidence of contagion is lower.

Pathogenesis

Varicella-zoster virus is an alpha-herpesvirus. Like all herpes group viruses, it is an enveloped, icosahedral virus that contains a double-stranded DNA genome. Chickenpox begins with replication of the virus at sites of contact and is followed by a primary viremia. A secondary viremia occurs after about 1 week, which disseminates the infection to the skin, causing the familiar rash to appear. As the acute disease abates, the virus establishes latency in sensory ganglia. Reactivation of latent infection causes zoster or “shingles,” which produces pain and a vesicular rash in the distribution of one to three dermatomes. Replication of the virus in the ganglia is destructive to ganglion cells, which may account for the pain associated with zoster. Unlike herpes simplex virus (HSV) 1 or 2, which can reactivate frequently, it is uncommon for VZV to reactivate more than once. The exception is chronic or recurrent zoster that has been seen with some frequency in patients who have acquired immunodeficiency syndrome. Exactly what precipitates reactivation of the latent virus is not clear. The incidence of zoster increases with age, however, and this has been correlated with decreasing cell-mediated immunity to VZV. Immunity to varicella appears to be lifelong; that is, second clinical cases of varicella are rare.

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  2. […] Varicella in the immunocompromised host can be severe and life-threatening. Cell-mediated immunity appears to be the most important factor in the prognosis of primary varicella infection, as evidenced by the fact that patients who have pure humoral immune deficiency syndromes (such as Bruton agammaglobulinemia) do not seem to experience severe or protracted disease. As in immunocompetent individuals, administration of VZIG can prevent symptomatic infection, but it cannot clear an established infection. Generic medications online Patients who have reticuloendothelial tumors and leukemia are at particularly high risk for severe disease. Risk is increased by concomitant administration of immunosuppressive therapeutic agents. Approximately 20% of patients who have leukemia develop “progressive varicella,” with fever to 40.5°C (105°F), continued cutaneous eruption for 7 to 10 days, deeper skin lesions, and diffuse involvement that includes palms and soles. Patients who have leukemia have difficulty clearing the viremia, and the virus disseminates to internal organs, most frequently the lung, but also the liver or central nervous system. Visceral dissemination occurs in from 7% to 32% of patients who have leukemia. VZV also causes substantial mor-bidity and mortality in bone marrow transplant recipients. One report of 140 patients documented zoster in 77, dissemination in 22, and death in 7. Canadian viagra The incubation period of VZV may be either shortened or prolonged in patients who are immunosuppressed and ranges from 8 to 24 days or even longer. The median is about 19 days. The incubation period is longer in those who receive VZIG. […]

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